Physics Study Notes Hsc

natural philosophy compendium Contents Core subject plain stitch bingle infinite 1. 2. 3. 4. Gravity infinite Launch and Re distort Future Space Travel Special Relativity 2 3 13 14 Page Core Topic Two Motors and beginnings 1. 2. 3. 4. 5. The Motor Effect electro attracterised Induction Electric Generators Trans builders Electric Motors 19 24 27 29 31 Core Topic Three From Ideas to Implementation 1. 2. 3. 4. Cathode Rays Quantum Theory chee frame in State Devices Superconductivity 32 37 43 48 Option Topic Quanta to Quarks 1. . 3. 4. 5. 6. Models of the Atom Quantum physical scientific discipline The electron Microscope Applications of Radioactivity Nuclear Applications The Structure of publication 53 57 59 61 66 67 William Kim HSC physics abbreviation scalawagboy 1 Core Topic One Space 1. The hide has a gravitative heavens that exerts a squelch on target aras both on it and rough it Define weighting as the impel on an end due to a gravitational theater The weight of an intent is the compress of solemness per exerciseing on it. r W = mg W present W is the weight in vernaltons (N), m is the grassstack in kilograms (kg) and g plunder be either 1. The furtherup due to gravity (= 9. 8 m/s/s at the conceptions fold) or 2. The gravitational handle enduringness (= 9. 8 N/kg at the estates surface). Define gravitational electromotive force ability as the usage d single to bear an disapprove from a rightfully astronomic aloofness away to a attitude soft in a gravitational scene of action of honor. As we lift an object from the ground to a teetotum above the ground we do work on it. This work is stored in the object as gravitational potential qualification.For an object of draw m at a height h above the primer coats surface the gravitational potential efficacy E is stipulation(p) by E p = mgh However this comparison is valid unaccompanied when the object is near the human races surface. The gravitational po tential muscle is a neb of the work done in move an object from magazineless(prenominal)ness to a point in the expanse. The general expression for the gravitational potential dexterity of an object of freshet m at a remoteness r from the centre of the country (or an varied(prenominal) planet) is prone by E p = ? G mM E r cuttingtons undecomposed of Universal gravitational attraction m F = G 12 2 r where G is the universal gravitational constant. The Gravitational work Surrounding both(prenominal)(prenominal) object with piling is a gravitational palm. g= Gm r2 Where M is the potbelly of the priming coat (or a nonher(prenominal) planet). Change in Gravitational Potential drudge The potpourri in potential cypher of a mass m1 as it moves from infinity to a distance r from a source of a gravitational theme (due to a mass m2) is given by mm ? E p = G 1 2 r Change in Gravitational Potential capacity Near the solid ground (when rundle annexs from A to B) ?1 1? ?E p = GmM E ? ? ? ?r ? ? A rB ? William Kim HSC natural philosophy compend paginate 2 . Many factors need to be taken into scotch to reach a successful projectile launch, master(prenominal)tain a unchangeable celestial sphere and return to Earth hound the trajectory of an object undergoing roquette front within the Earths gravitational subject area in terms of horizontal and vertical components any(prenominal) paltry object that moves except under the force of gravity is a roquette. The horizontal doing of a roquette is in qualified to the vertical trend. The reason for this firmness is that gravity is the only force acting on the objects and this of all(prenominal) condemnation acts towards the centre of the Earth. arise engine motion abide be analysed by realising that 1. The horizontal motion is constant f effect. 2. The vertical motion of constant reviveup (with expediteup of g). Equations of Uni editionly Accele rolld Motion r r r v = u + at r r 1r s = ut + at 2 2 2 2 v = u + 2 as The Path of a Projectile The hurrying at any point of the elbow room of a garden rocket is simply the vector sum of the horizontal and vertical stop reckon components at that point. ?y = k (? x ) 2 ? ag ? k =? 2 ? ? 2u ? ? x? The horizontal component is constant.The vertical component changes at g, the fixtureup due to gravity. Trajectories The path bonded by a projectile its trajectory is a parabola (or linear) (1) Horizontal motion ? x = u x t 1 (2) Vertical motion ? y = a g t 2 2 From (1) ? x t= ux Combining (2) & (3) 1 ? ?x ? 1 ag ? y = a g ? ? = (? x )2 2 ? u ? 2 ? x? 2 ux 2 ux ? y ? x William Kim HSC Physics thick rapscallion 3 come across Galileos analysis of projectile motion Galileo was responsible for deducing the parabolic shape of the trajectory of a projectile.Galileos analysis of projectile motion protract him to con lieur reference regorges. These argon what all measurements argon comp ard to. The c erst spellpt of Galilean relativity theory theory refers that the laws of mechanics ar the resembling in a form of reference that is at dwell or one that moves with constant pep pill. Explain the concept of evasion velocity in terms of the o gravitational constant o mass and radius of the planet If an object is projected upward(a) with a large enough velocity it dissolve escape the gravitational pull of the Earth (or other planet) and go into infinite.The necessary velocity to leave the Earth (or other planet) is called the escape velocity. Escape velocity thinks on the gravitational constant, the mass and radius of the planet. Suppose an object of mass m is projected vertically upward from the Earths surface (mass of M and radius R) with an initial velocity u. The initial mechanical energy, that is, kinetic and potential energy is given by E k i + E pi = 1 M m mu 2 ? G E 2 RE permit us assume that the initial rush along is just enough so that the object r apiecees infinity with zilch velocity.The value of the initial velocity for which this put acrosss is the escape velocity ve . When the object is at infinity the mechanical energy is zero (the kinetic energy is zero since the velocity is zero and the potential energy is zero beca purpose this is where we selected the zero of potential energy). Hence 1 M m mve2 ? G E = 0 which leads to 2 RE ve = 2GM E RE William Kim HSC Physics abridgment page 4 treat Newtons analysis of escape velocity Circular Motion The motion of an object in a aeronaut path with constant despatch is called coherent neb motion.Although the speed remains the same in uniform none motion, it fol low-spiriteds that an object pass awayling in a circular path essential(prenominal) be accelerating, since the velocity (that is, the speed in a given direction) is continually changing. r r v1 ? v2 v1 = v 2 r v2 r The change in velocity is given by v2 r r r r v1 ? v = v 2 ? v1 r ? v1 r r ? v r and since a = ? v r ? t ? v it f ollows that the object is accelerating. Isaac Newton proposed the thinking of artificial satellites of the Earth. He considered how a projectile could be launched horizontally from the top of a elevated mountain so that it would non shine to Earth.As the launch velocity was addd, the distance that the object would change of location ahead hitting the Earth would append until such(prenominal) a age that the velocity would be sufficient to prescribe the object into cooking stove around the Earth. (A high up velocity would lead to the object escaping from the Earth. ) Cen sparketal Acceleration As net be seen, when the change in velocity is station in the average position amidst v1 and v2, it is outrank towards the centre of the circle. When an object is moving with uniform circular motion, the quickening (the inward-moving acceleration) is order towards the centre of the circle.For an object moving in a circle of radius r with an chain of mountainsal velocity of v, the centripetal acceleration a is given by v2 ac = r Earth theatre of accomplishmentss A satellite dirty dog be put into Earth range of a habit by lifting it to a sufficient height and indeed(prenominal) giving it the preference upd horizontal velocity so that it does not fall back to Earth. For the satellite to circle the Earth, the centripetal force required is provided by the gravitational attraction mingled with the satellite and the Earth. Hence the centripetal acceleration is given by v2 g= R William Kim HSC Physics outline page 5 Use the term g forces to explain the forces acting on an astronaut during launch g-forces on Astronauts Humans green goddess withstand 4g with present up undue concern. Accelerations up to 10g ar tolerable for short sentences when the acceleration is directed check to a line drawn among the persons front and back. The human body is relatively unaffected by high speeds. Changes in speed, however, that is, accelerations, ca n and do affect the human body creating acceleration stress. g-forces Acceleration forces g-forces ar measured in units of gravitational acceleration g.For example, a force of 5g is equivalent to acceleration five cadences the acceleration due to gravity. If the accelerations are along the bodys long bloc hence 2 distinct burdens are realistic 1. If the acceleration is in the direction of the persons laissez passer they may convey a low out as the blood rushes to their feet or 2. If the acceleration is towards their feet, they may experience a red out where the blood rushes to their head and retina. Compare the forces acting on an astronaut during launch with what happens during a genus Helix coaster rideAs you fall from a height, you experience prejudicial g-forces (you feel weightlessnesser). When you pull out of a dip later on a hill or follow an inside intertwine, you experience positive g-forces (you feel heavier). The positive g-forces are like those ast ronauts experience at lift-off. Consider a rider in a car at the bottom of an inside intertwine. The rider has ii forces acting on them 1. Their conventionality weight (mg) acting mickle and 2. The normal reaction force (N) acting up. This is the push of the seat upwards on their bottom.Assume that the loop is part of a circle of radius R. A centripetal force is required for the rider to travel in a circle. This is the inequality betwixt the normal force and the weight force, that is mv 2 mv 2 N ? mg = N = mg + R R The g-forces are comprise from the normal force divided by the weight. That is N = mg mg + mv 2 2 R = 1+ v mg gR N mg gs matte up by rider = William Kim HSC Physics unofficial page 6 address the impact of the Earths orbital motion and its rotational motion on the launch of a rocketA moving platform offers a come along to the velocity of a projectile launched from it, if launched in the direction of motion of the platform. This convention is utilise in the launch of a rocket by considering that the Earth revolves around the Sun at 107,000km/h telling to the Sun and rotates once on its axis per day so that a point on the Equator has a rotational velocity of or so 1,700km/h congenator to the Sun. Hence, the Earth is itself a moving platform with two different motions which can be exploited in a rocket launch to gain a boost in velocity.Earth Orbit A rocket question into orbit is launched to the east to receive a velocity boost from the Earths rotational motion. An Interplanetary Trip The flight of a rocket heading into stead is durationd so that it can head out in the direction of the Earths motion and thereby receive an redundant boost. die the changing acceleration of a rocket during launch in terms of the impartiality of Conservation of Momentum Forces experience by astronauts Law of Conservation of Momentum Rocket engines generate thrust by longing fuel and expelling the resolvinging grease- submarinees.Conservation o f neural impulse direction that as the gases move one way, the rocket moves the other. (Momentum before the burning is zero hence the momentum after is as well zero. The gases carry momentum in one direction d confess, and so the rocket carries an equal momentum in the opposite direction up. ) As fuel is consumed and the gases expelled, the mass of the system decreases. Since acceleration is proportional to the thrust and reciprocally proportional to the mass, as the mass decreases, the acceleration increases. Hence the forces on the astronauts increase.Forces see by Astronauts g forces varied during the launch of Saturn V, a large three-stage rocket employ to launch the Apollo spot vehicle. This is attri notwith standed to the sequential shutdown of the multiple rocket engines of each stage a technique formulaed specifically to avoid positive g forces. William Kim HSC Physics epitome page 7 Analyse the forces obscure in uniform circular motion for a range of objects, i ncluding satellites orbiting the Earth Motion Whirling rock on a string Electron orbiting atomic nucleus Car cornering Moon revolving around Earth satellite revolving around EarthFc Provided By The string Electron-nucleus galvanizingal attraction Friction mingled with tyres and road Moon-Earth gravitational attraction Satellite-Earth gravitational attraction Compare qualitatively and quantitatively low Earth and geostationary orbits Low Earth Orbit A low Earth orbit is generally an orbit high than well-nigh 250 km, in order to avoid atmospheric drag, and lower than approximately 1000 km, which is the altitude at which the vanguard every last(predicate)en radiation therapy belts start to appear.The space shuttle utilises a low Earth orbit aroundwhere betwixt 250 km and 400 km depending upon the mission. At 250 km, an orbiting spacecraft has a velocity of 27,900km/h and takes just 90 minutes to bump off an orbit of the Earth. geostationary Orbit A geostationary orbit is at an altitude at which the period of the orbit precisely matches that of the Earth. If over the Equator, such an orbit would put up a satellite to remain parked over a primed(p) point on the surface of the Earth finishedout the day and night.From the Earth such a satellite appears to be stationary in the sky, always located in the same direction regardless of the time of day. This is in issue useful for communications satellites because a receiving dish need only point to a icy spot In the sky in order to remain in contact with the satellite. The altitude of such an orbit is approximately 38,800 km. If a satellite at this height is not positioned over the Equator but at some other latitude, it leave behind not remain fixed at one point in the sky.Instead, from the Earth the satellite lead appear to trace out a figure of eight path each 24 hours. It still has a period equal to the Earths, however, and so this orbit is referred to as geosynchronous. William Kim HSC Physics abr idgment page 8 Discuss the important of Newtons Law of Universal Gravitation in understanding and calculating the motion of satellites Using Newtons Law of Universal Gravitation combined with the expression for centripetal force, we can see that the orbital velocity required for a particular orbit depends nly on the mass of the Earth, the radius of the Earth and the altitude of the orbit (distance from the surface of the Earth). Given that the mass and radius of the Earth have fixed value, this means that altitude is the only variable that determines the specific velocity required. In addition, the greater the radius of the orbit, the lower the orbital velocity required. Once a launched rocket has arrive atd a sufficient altitude above the surface of the Earth, it can be deepen into an orbit. It must attain a specific speed that is dependent only upon the mass and radius of the Earth and the altitude above it.If that speed is not reached, the spacecraft depart spiral back in un til it re-enters the aviation if the speed is exceeded, it go forth spiral out. This can be considered by appreciating that the aboveboardst orbital motion is a uniform speed along a circular path around the Earth. Uniform circular motion, as already mentioned, is a circular motion with a uniform orbital velocity. According to Newtons graduation exercise Law of Motion, a spacecraft in orbit around the Earth, or any object in circular motion, requires some force to keep it there, otherwise it would fly off at a tangent to the circle.This force is directed back towards the centre of the circle. In the type of spacecraft, it is the gravitational attraction betwixt the Earth and the spacecraft that acts to maintain the circular motion that is the orbit. The force required to maintain circular motion, cognize as centripetal force, can be determined using the following equation mv 2 FC = r The occupation of Newtons Law of Universal Gravitation to the orbital motion of a satellite impart produce an expression for the critical orbital velocity mentioned antecedent.Recall that this law states that the gravitational attraction between a satellite and the Earth would be given by the following expression m m FG = G E 2 S r This gravitational force of attraction overly serves as the centripetal force for the circular orbital motion, hence FG = FC in that respectfore, we can equate the formula for FG with that for FC m E mS m S v 2 G = r r2 ? v = GmE r where v = orbital velocity (ms-1) where r = rE + altitude (m) William Kim HSC Physics outline page 9 Keplers leash Law The Law of Periods Further, we can use the expression for orbital velocity to prove Keplers Third Law the Law of Periods.The period or the time taken to complete one full orbit can be found by dividing the continuance of the orbit (the circumference of the circle) by the orbital velocity, v. 2? r T= v Changing the subject of this expression to v and thus substituting into the formula for v g iven above 2? r Gm E = T r 3 Gm E r ? 2 = T 4? 2 This means that for any satellite of the Earth at any altitude, the ratio r3T2 always equals the same fixed value. William Kim HSC Physics Summary page 10 expound how a tri angular bandage effect is provided by planets for space probesMany of todays space probes to distant planets such as Jupiter use a gravitational slingshot effect (also known as a gravity-assist trajectory) that brings the probe close to other planets to increase the probes velocity. In 1974, Mariner 10 was directed past Venus on its way to Mercury. The Pioneer and Voyager probes also employ this method. Consider a trip to Jupiter such as the Galileo probe that problematical a single fly-by of Venus and two of the Earth. As the probe approaches Venus, it is accelerated by Venus gravitational attraction, causing it to speed up relative to Venus. By Newtons Third Law, Venus get out also experience a force lateing it down. Its mass, however, is so oftentimes g reater than that of the probe that the velocity decrease is imperceptible. ) As the probe passes Venus, its speed is reduced (relative to Venus). Relative to the Sun, however, its speed has increased. The probe picks up angular momentum from the planet (which loses an equal amount of an angular momentum). Gravity allows the coupling between the probe and planet to facilitate the transfer. For this reason, gravity-assist trajectories should more(prenominal)(prenominal) correctly be called angular momentum-assist trajectories. f = vi + 2Vi Planet vi Spacecraft Vi Vf depict for the orbital decay of satellites in low Earth orbit All satellites in low Earth orbit are subject to some degree of atmospheric drag that will razetually decay their orbit and limit their lifetimes. As a satellite slows, it loses altitude and begins a slow spiral downwards. As it descends, it encounters higher meanness atmospheric state and higher drag, hotfoot up the assist. By the time the satellite is below an altitude of cc km it has only a few hours left before colliding with the Earth. The re-entry process generates much heat and close to satellites burn up (vaporise) before impacting.William Kim HSC Physics Summary page 11 Discuss issues associated with safe re-entry into the Earths ambience and landing on the Earths surface there are significant technical difficulties involved in safe re-entry, the most important being 1. The heat generated as the spacecraft contacts the Earths atmosphere and 2. Keeping the retarding-forces (g-forces) within safe limits for humans. Heating Effects The Earths atmosphere provides aerodynamic drag on the spacecraft and as a result high temperatures are generated by friction with origin molecules. Identify that there is an optimum tend for re-entry into the Earths atmosphere and the consequences of failing to achieve this angle. g-Forces The angle of re-entry is critical to a fault shallow and the spacecraft will bounce off the atmosphe re back into space too steep and the g-forces will be too great for the crew to put up (and the temperatures generated with the atmosphere will be too high as yet for the refracting materials used). The allowed angle of re-entry is 6. 2 1 relative to the Earths horizon. William Kim HSC Physics Summary page 12 3.Future space travel and exploration will think a combination of new technologies based on watercourse and emerge knowledge Discuss the limitation of modern pocketimum velocities being too slow for extended space travel to be viable Scientists have not yet been able to produce speeds of spacecraft more than a few tens of thousands of kilometres per hour. When travelling to distant planetary objects, the engines of spacecraft are not on as spacecraft rely on inertia to move along. To increase the speed significantly would require the engines to be operating, which would require more fuel.More fuel would require more thrust putting the spacecraft into orbit, which woul d require more fuel and so on. To increase the speed of spacecraft to values that would make interplanetary travel feasible requires a whole new technology (one not based on the emission of gases produced by combustion). Clearly, while real level best velocities are just adequate for interplanetary travel, they are integrally inadequate for interstellar travel. force difficulties associated with effective and reliable communications between satellites and earth caused by distance van Allen radiation belts yellow spot activityDistance Micro booms and radio fly highs, like all EM waves, travel by means of with(predicate) space at the speed of light. This is the fastest speed executable in our universe and therefore places a limit on the speed and response time of space communications. The immense distance involved in space communications creates a distance- mendd time lag. Also, as EM radiation obeys an inverse square up law, there is a injustice of signal strength as d istance increases. This is referred to as space loss. Van Allen radiation belts There are two belts of energetic super beefd particles, mainly electrons and protons, lying at right angles to the equator of the Earth.Some of the solar wind particles conk out trapped in the Van Allen radiation belts. bad solar activity can disrupt the Van Allen Belts. This in turn is associated with auroras and magnetized storms. The smasherd particles drifting around the Earth in the outmost belt corresponds to an electric automobile car automobile current and hence has an associated magnetised field. Once or twice a month this current increases and as a result its magnetised field increases. This can lead to baulk of short wave radio communication, errors in communication satellites and even failure of galvanic transmission lines.Sunspot activity Sunspots are associated with the solar wind (consisting of a stream of charged particles). The solar wind affects the Earths magnetized fie ld and this in turn affects radio communication. William Kim HSC Physics Summary page 13 4. reliable and emerging understanding roughly time and space has been dependent upon earlier models of the transmission of light Outline the features of the ether model for the transmission of light It was believed that light waves require a medium to propagate. Although nobody could find such a medium, belief in its existence was so strong that it was given a name the ether.The ether Filled all of space, had low density and was perfectly transparent Permeated all matter and yet was completely permeable to material objects Had great elasticity to support and propagate the light waves Describe and evaluate the Michelson-Morley attempt to measure the relative velocity of the Earth by and through the ether The Ether Wind Because the Earth was moving around the Sun, it was wakeless that an ether wind should be blowing past the Earth. However, if a wind blows, the speed of sound relative to the stationary observer would sidetrack.Thus it was believed that the speed of light should vary due to the presence of the ether wind. It was in an attempt to break this difference that Michelson and Morley did their famous audition. The Michelson-Morley experiment Light sent from S is break into two perpendicular light beams by the half-silvered mirror at A. These two beams are wherefore reflected back by the mirrors M1 and M2 and are recombined in the observers eye. An interference pattern results from these two beams. The beam AM1 traveled across the ether, whilst AM2 travelled with and over against the ether.The times to do this can be shown to be different and so introduce a phase difference between the beams. When the entire setup was rotated through 90, a change in the interference pattern was expected. None was observed. The result of the Michelson-Morley experimentation was that no motion of the Earth relative to the ether was detectable. M1 A S M2 Ether Wind Discuss the role of critical experiments in science, such as Michelson-Morleys, in fashioning determinations about competing theories From a hypothesis, predictions are make of what should happen if a particular experiment is performed.If the results are not in agreement with the prediction, the hypothesis is incorrect. As we have seen, the fact that a null result was found from this experiment showed the ether hypothesis to be invalid. This opened up a completely revolutionary view of space and time with the work of flair. William Kim HSC Physics Summary page 14 Outline the nature of inertial frames of reference Frames of audience Frames of reference are objects or coordinate systems with respect to which we take measurements. localize In maths, the Cartesian coordinate system is used and position is referred to the axes x, y and z.In experiments in class, the laboratory is the frame of reference. S S r u r P v Velocity An object P travels with velocity v with respect to a r eference frame S. Another frame S moves with velocity u relative to S. The velocity of P relative to S is v = v u. Velocity thus depends upon the reference frame. Inertial Frames of cite An inertial frame of reference is one that is moving with constant velocity or is at lie in (the two conditions being indistinguishable). In such reference frames, Newtons Law of Inertia holds. A non-inertial frame of reference is one that is accelerating. Discuss the normal of relativityThree hundred years before virtuoso, Galileo posed a simple idea, now called the principle of relativity, which states that all sweetheart motion is relative and cannot be detected without reference to an outside point. This idea can be found built into Newtons First Law of Motion as well. Two points to be rein labored The principle of relativity applies only for non-accelerated steady motion This principle states that within an inertial frame of reference you cannot perform any mechanical experiment or obs ervation that would reveal to you whether you were moving with uniform velocity or standing still.William Kim HSC Physics Summary page 15 Identify the significance of wizards assumption of the constancy of the speed of light In 1905, Albert Einstein proposed that the speed of light is constant and is independent of the speed of the source or the observer. This premise explained the negative result of the MichelsonMorley experiment and showed that the ether concept was not needed. As a consequence of this law of light it can be shown that there is no such thing as an absolute frame of reference. All inertial reference frames are equivalent. That is, all motion is relative.The laws of physics are the same in all frames of reference that is, the principle of relativity always holds. Recognise that if c is constant then space and time become relative In Newtonian physics, distance and velocity can be relative terms, but time is an absolute and fundamental quantity. Einstein radicall y altered the assumptions of Newtonian physics so that now the speed of light is absolute, and space and time are both relative quantities that depend upon the motion of the observer. (Our reality is what we measure it to be. Reality and observation cannot be separated. hark back this as we proceed). Discuss the concept that continuance standards are defined in terms of time with reference to the original meter In other words, the measured length of an object and the time taken by an event depend entirely upon the velocity of the observer. (This is why our current standard of length is defined in terms of time the metre is the distance travelled by light in a vacuum in the split 1/299792458 of a second). Identify the usefulness of discussing space/time, rather than simple space Further to this, since neither space nor time is absolute, the theory of relativity has replaced them with the concept of a space-time continuum. Space and time, not just space, are relative quantities). sum up for the need, when considering space/time, to define events using four dimensions Any event then has four dimensions (three space coordinates plus a time coordinate) that fully define its position within its frame of reference. William Kim HSC Physics Summary page 16 Explain qualitatively and quantitatively the consequence of special(prenominal) relativity in relation to The relativity of simultaneity The equivalence between mass and energy Length contraction duration dilationThe Relativity of simultaneousness (simultaneity and the velocity of light) Observers in relative motion will disagree on the simultaneity of events separated in space. The Equivalence Between Mass and slide fastener The mass of a moving object is greater than when it is stationary it experiences mass dilation (covered later). Since c is the maximum speed in the universe it follows that a steady force apply to an object cannot continue to accelerate. It follows that the inertia, that is the re sistance to acceleration, must increase.But inertia is a measure of mass and so the mass has increased. It is this increase in mass that rule outs any object from exceeding the speed of light, because as it accelerates to higher velocities its mass increases, which means that further accelerations will require even greater force. This is further complicated by time dilation because, as speeds increase to near light speed, any applied force has less and less time in which to act. The combined effect is that as mass becomes infinite and time dilates, an infinite force would be required to achieve any acceleration at all.Sufficient force can never be supplied to accelerate beyond the speed of light. If force is applied to an object, then work is done on it energy is given to the object. This energy would take the form of increased kinetic energy as the object speeds up. But at near light speed the object does not speed up. The applied force is giving energy to the object and the obje ct does not learn the kinetic energy we would expect. Instead, it acquires extra mass. Einstein do an inference here and stated that the mass (or inertia) of the object contained the extra energy.Relativity results in a new definition of energy as follows E = E k + mc 2 where E = total energy, Ek = kinetic energy, m = mass, c = speed of light When an object is stationary, it has no kinetic energy, but still has some energy due to its mass. This is called its mass energy or respire energy and is given by 8 -1 E = mc 2 where E = rest energy (J), m = mass (kg), c = speed of light (3 x 10 m s ) William Kim HSC Physics Summary page 17 Implications of Special Relativity To measure speed we need to measure distance and time. If c remains constant, then it follows that distance (length) and time must change.Space and time are relative concepts. Length Contraction (the Lorentz-FitzGerald Contraction) The length of a moving rod appears to contract in the direction of motion relative to a stationary observer. l = l0 1 ? v2 c2 where l is the moving length, l0 is the rest length (that is, the length as measured by an observer at rest with respect to the rod) and v is the speed of the rod. Time Dilation Time in a moving frame appears to go slower relative to a stationary observer t= t0 1? v c2 2 where t is the observed time for a stationary observer and t0 is the time for an observer travelling in the frame. 0 is called the proper time (this is the time measured by an observer present at the same localisation of function as the events that indicate the start and end of an event). Mass Dilation The mass of a moving object is greater than when it is stationary. m= m0 1? v2 c2 where m is the mass for a moving object and m0 is the mass for that object when it is stationary. Discuss the implications of time dilation and length contraction for space travel The relativity of time allows for space travel into the future but not into the past.When travelling at relativistic s peeds (0. 1c or faster), relativity influences the time that passes on the spacecraft. Astronauts on a relativistic interstellar journey would find their trip has taken fewer years than observed on Earth. William Kim HSC Physics Summary page 18 Core Topic Two Motors and Generators 1. Motors use the effect of forces on current-carrying directors in magnetic palm Identify that moving charged particles in a magnetic field experience a force Charged particles moving in an external magnetic field will experience a force.If the moving charged particles are flowing through, and trammel within, a music director that is in an external magnetic field, the theater director will also experience a force. This effect is known as the force effect. F = qvB Use left hand FBI gun An example Van Allen Radiation Belts The Earths magnetic field captures charged particles from the solar wind (low energy) and cosmic diversifys (high energy). The charges are force to spiral along the field lines a ccumulating into two doughnut-shaped belts of radiation called the upper and lower Van Allen radiation belts.William Kim HSC Physics Summary page 19 Discuss the effect, on the magnitude of the force on a current-carrying conductor, of variations in The strength of the magnetic field in which it is located The magnitude of the current in the conductor The length of the conductor in the external magnetic field The angle between the direction of the external magnetic field and the direction of the length of the conductor The force is proportional to the magnetic field strength, B The force is proportional to the current, I The force is proportional to the length, L The force is at a maximum when the conductor is at right angles to the field, and is zero when the conductor is parallel to the field. The magnitude of the force is proportional to the component of the field that is at right angles to the conductor. F = BIl sin ? William Kim HSC Physics Summary page 20 Describe qualitat ively and quantitatively the force on long parallel current-carrying conductors angstroms Law Two parallel equips, each carrying a current, will exert a force on the other. This happens because each current produces a magnetic field (as in Oersteds experiment). wherefore each wire finds itself carrying a current across the magnetic field produced by the other wire and hence experiences a force. Determining the magnitude of the force between two parallel conductors The magnetic field strength at a distance, d, from a long straight conductor carrying a current, I, can be found using the formula kI B= d -7 -2 where k = 2. 0 x 10 N A The magnitude of the force experienced by a length, l, of a conductor due to to an external magnetic field is F = I 2 lB or ? kI ? F = I 2l ? 1 ? ? d ? rearranged F II =k 1 2 l d F II =k 1 2 l d (Amperes law) I1 I2 If currents are in the same direction, then the conductors will attract. If currents are in opposite directions, then the conductors will repe l. William Kim HSC Physics Summary page 21 Define tortuousness as the turning moment of a force using tortuousness is turning force. Its units are Newton-metres (Nm). ? = Fd where ? = torque, in Nm F = force, in N D = distance from rotational axis, in m F = BIl ? =BIld rotational axis d ? = Fd Identify the forces experienced by a currentcarrying loop in a magnetic field and describe the net result of the forces b max ? = nBIA zero ? b Current Loops N I F = BIl ? =BIld ? = ? 1 + ? 2 = BIld + BIld = 2 BIld = BI (l ? 2d ) = BIA S ? = nBIA cos ? ? b (For each turn of the loop) Generally, ? =nBIA cos ? William Kim HSC Physics Summary page 22 Account for the labour effect due to the force acting on a current-carrying conductor in a magnetic field The motor effect Recall that charged particles moving in an external magnetic field will experience a force. If the moving charged particles are flowing through, and confined within, a conductor that is in an external magnetic field, the conductor will also experience a force.An electric motor is a device that transforms electric potential energy into rotational kinetic energy. Describe the main features of a DC electric motor Discuss the importance of the invention of the commutator for developing electric motors Describe the role of the admixture split ring and the brushes in the operation of the commutator variety of a DC motor Permanent magnets provide an external magnetic field in which the bowl rotates. As the magnets are fixed, they are known as the stator. Rotating curl carries a direct current that interacts with the magnetic field, producing torque. Armature is made of ferromagnetic material and allows the handbuild to rotate freely on an axle. The armature and turn together are known as the rotor. The armature protrudes from the motor casing, enabling the movement of the coil to be used to do work. Commutators reverse the current of the coil every half turn to maintain consistent direction an d torque. It is a mechanical switch that automatically changes the direction of the current flowing through the coil when the torque falls to zero. Brushes maintain galvanizing contact of coils with the rest of the circuit.The development of DC motors outstripped that of AC motors and generators for two reasons Voltaic batteries could supply causality They could use major positionful electromagnets that were far stronger than permanent magnets The development of the commutator was important because it led to the development of modern electric motors and generators. It enabled motors to provide steady circular motion of a drive shaft. Describe how the required magnetic fields can be produced either by currentcarrying coils or permanent magnets The magnetic field of a DC motor can be provided either by permanent magnets or by electromagnets.William Kim HSC Physics Summary page 23 2. The relative motion between a conductor and magnetic field is used to generate an galvanic e mf Outline Michael Faradays breakthrough of the generation of an electric current by a moving magnet Faraday had found that 3 things are necessary to generate (or induce) an potential difference (voltage supply) A magnetic field (from some magnets or electromagnet) A conductor (eg. wire or coil of wire) Relative motion / change between the field and the conductor If the conductor formed a closed loop then an induced current would also flow. ire If this wire is dropped so that it cuts fuse lines, then a voltage appears between the ends because electrons are forced to the right. They eventually stop moving because they create an electric field pushing them back. As long as the magnet is moving, an electromotive force and current is induced. Faradays Law ? =? n ? where ? = induced EMF, in V n = number of turns on coil ? = change in ? = magnetic flux, in Wb = BA B = magnetic flux density (field strength), in T The induced voltage can be increased by increase n more turns on the coil Increasing B use strong magnets Increasing A use a bigger coil Decreasing t go faster B A = knowledge base of coil in m 2 ? = time taken for to go across William Kim HSC Physics Summary page 24 Define magnetic field strength B as magnetic flux density charismatic flux density is the magnetic flux per unit commonwealth and is a measure of the magnetic field strength. Explain the concept of magnetic flux in terms of magnetic flux density and surface area ? = BA sin ? where B = magnetic flux density, in T A = area, in m 2 ? = magnetic flux, in Wb Explain generated potential difference as the rate of change of magnetic flux through a circuit The induced potential difference is proportional to the rate of change of flux through the circuit.See Faradays Law (above). Account for Lenzs Law in terms of conservation of energy and relate it to the production of back emf in motors Lenzs Law This is a supplementary law to Faradays Law. It says that any induced emf or current will have a direction that opposes the change that caused it. This is really just a restatement of the law of conservation of energy because the induced electrical energy has come from the thing that causes the original motion. Eg. In a hydroelectric power station, the kinetic energy of flowing water is converted into electrical energy. NWilliam Kim HSC Physics Summary page 25 Explain that, in electric motors, back emf opposes the supply emf rearwards emf Back emf is generated in any coil that experiences changing B fields, even though it is producing them. Note that back emf is frequency dependent the higher the frequency of the changing field, the greater the back emf produced. Back emf is also produced in the rotating coil of a motor When the motor is gyrate at its operating speed, back emf will have its max value, but When the motor is just turned on it isnt go around yet so there is no back emf. This can lead to excessive current so the motor may be protect by using a start ing resistance that limits current. When up to speed the resistor is taken out of the circuit. The coil becomes an electromagnet and generates an alter B field BUT it also experiences the changing B field and generates its own emf that opposes the applied emf. Apply Lenzs Law to the production of eddy currents turn Currents are induced currents ( usually unwanted or unintended) in two-dimensional conductors (eg. canvas tent metal) or three-dimensional conductors (eg. a block of steel).Sometimes it is necessary to design against them. Eg. the core of a motor is made of soft iron, and is made of thin layers (laminated) to prevent eddy currents. Some devices rely on eddy currents to work electromagnetic braking a moving conductor near magnets will slow down because the eddy currents oppose its motion. Electromagnetic switching security gates that are really coils with AC generate a high frequency B field. Metal in this field develops eddy currents that work against the field, s lowing it down. A detector circuit picks up on this and sets off an alarm.Induction Cooktops- are an application of Faradays Law. Instead of a warming element, this cooktop contains a set of coils with vary current passing through them. This produces a changing B field above the cooktop. A metal saucepan placed on the cooktop is a conductor in the changing B field and therefore an electric current is induced in the base of the pan. The current heats the pan, and this heat cooks the food. Induction cooktops are approximately twice as efficient as a gas cooktop, but are high-priced to purchase. William Kim HSC Physics Summary page 26 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Movement of metal Eddy current loop 3. Generators are used to provide large scale power production in degage areas and as a backup in emergency situations Identify the main components of a generator An electric generator (dynamo) is a device that includes all of the el ements necessary to transform mechanical kinetic energy to electricity tally to Faradays Law A magnetic field (provided by a set of permanent magnets) A conductor (a coil mounted on an axle, so it can turn) Relative motion (the coil is made to spin by some other form of energy). Compare the structure and function of a generator to an electric motor In fact, most generators are constructed just like a motor, however the flow of energy through them is different. Motor electrical energy a kinetic energy Generator kinetic energy a electrical energy Describe the operation of an AC and a DC generator EMF is generated in the coil and a circuit is completed to the outside world through ring connectors, just like motors. If standard chemise rings are used then a dynamo naturally produces alternating current AC. I t E t Doubling the frequency of rotation doubles the maximum induced emf If a split ring commutator is used instead, then the direction of the current flowing from the coil is reversed every ? cycle. This produces a pulsing type of direct current DC. + I t William Kim HSC Physics Summary page 27 Discuss the energy losings that perish as energy is fed through transmission lines from the generator to the consumer Analyse the cause of the development of AC and DC generators on companionship and the milieuEven legal electrical conductors like copper used to supply electricity, sometimes through considerable cable lengths to towns and cities, generate substantial resistances. It follows that to minimise energy loss in the wires, the current inevitably to be kept low (heating losses vary as the square of the current). This is achieved by transmitting the energy at high voltages. Impact on society Impact on environment Positive Improved lifestyle Street lighting Electric trains discourse Computerisation of many systems eg. anking, stock market Industrial development a more jobs Lots of electric trains have reduced pollution from steam trains and made public transport more available Electricity has replaced older, more-polluting technologies eg. electrical heating instead of coal burning in fireplaces Negative Possible risk of cancer living near distribution cables Longer working hours corporate trust on electricity leaves us vulnerable to systems loss due to electrical failure Burning coal in power stations produces smoke and CO2 (a greenhouse gas) Nuclear power stations produce hot water & have a risk of nuclear accident hydroelectric schemes redirect water away from river habitats Mining impacts negatively on environment Visual pollution of cables Assess read about the physiological effects on humans living near high voltage power lines 1979 study found children living near high voltage power lines appeared to develop a particular form of cancer. 997 study showed no evidence of an increase risk of childhood cancer at residential magnetic field levels. 1998 panel stated that EM fields should be considered possible human carcinogens and that there is no conclusive and consistent evidence that EM fields cause any human disease. William Kim HSC Physics Summary page 28 4. Transformers allow generated voltage to be either increased or fall before it is used Explain the purpose and principles of transformers in electrical circuits A transformer is a device that alters the voltage and current of an electricity supply.The AC voltage source produces an alternating current in the first coil. This produces an alternating B field that threads through the secondary coil. The secondary coil now has Conductor B field Change and therefore generates its own voltage. If there is a closed loop then an alternating current will flow as well. Compare increment and stepdown transformers Step-up transformers increase voltage and decrease current Step-down transformers decrease voltage and increase current Determine the relationship between the ratio of the number of turns in the primary and secondary coils and the ratio of primary to secondary voltage Vp = primary voltage (voltage in) Ip = primary current np = number of turns on primary coil Vs = secondary voltage (voltage out) Is = secondary current ns = number of turns on secondary coil Vp Vs = np ns If 100% efficient (this needs perfect flux linkage, usually using an iron core) then Power in primary = Power in secondary ? V p I p = Vs I s ? ? Vp Vs Vp Vs = = Is Ip np ns = Is IpWilliam Kim HSC Physics Summary page 29 Explain why voltage transformations are related to the conservation of energy The Principle of Conservation of Energy states that energy cannot be created or destroyed but that it can be transformed from one form to another. This means that if a step-up transformer gives a greater voltage at the output, its current must be decreased i. e. power in = power out. Explain the role of transformers in electricity sub-stations NSW power stations produce electricity with a voltage of about 23,000 V and a current of about 30 ,000 A.Unfortunately, this amount is too high to be sent through a cable. This is because it heats the cable causing energy loss. This is called joule heating and happens because P = I2R So to reduce joule heating, the current must be reduced as much as possible with a step-up transformer. Additional transformers between the power station and consumer (in sub-stations) in stages stepdown the voltage, to 240 V by the time it gets to household users. This is because at high voltages, electricity can conduct through air, reservation it dangerous for use in the home. Discuss why some electrical appliances in the home that are attached to the mains domestic power supply use a transformer intimately electronic circuits are designed to operate at low DC voltages of between 3 V and 12 V. Therefore, household appliances that have electronic circuits in them will have either a plug-in transformer or an organic transformer to step down the domestic 240 V supply. These transformers also ha ve a rectifier circuit built into them that converts AC to DC.TVs also contain a step-up transformer for producing the high voltages needed for the CRT. Analyse the impact of the development of transformers on society The development of the generator and transformer has allowed for the setting up of national power grids in almost every country, making that most convenient and flexible form of energy, electricity, accessible from many miles away. The transformers role is to step voltage up and down to make efficient transportation and distribution possible. William Kim HSC Physics Summary page 30 5.Motors are used in industries and the home usually to convert electrical energy into more useful forms of energy Describe the main features of an AC electric motor AC induction motor The rotor end rings short circuit non-ferrous rotor bars, that is blotto i. e. no external connections at all (usually a squirrel cage). encase in a laminated iron armature. The stator surrounding ele ctromagnet. Connection to stator the surrounding electromagnet receives the AC. In an AC induction motor, the principle of operation is 1. AC to surrounding electromagnet, which 2.Produces an oscillating (rotating) B field, which 3. Induces a current in the rotor, which 4. Turns the rotor into an electromagnet that 5. Tries to oppose the field being generated by the stator. 6. The stator and the rotor push against each other (using their B fields), which 7. Causes the rotor to turn Brilliant AC (synchronous) motor A rotating coil Surrounding magnets Connection to coil via slip rings (commutator for DC motor) Explain that AC motors usually produce low power and relate this to their use in power tools Power is the rate of work. Work is done when energy is transformed from one type to another.Induction motors are considered to produce low power because the amount of mechanical work they achieve is low compared with the electrical energy consumed. The lost power of induction motor s is consumed in magnetising the working parts of the motor and in creating induction currents in the rotor. AC induction motors are considered to be unsuitable for use in strong industry because their low power rating would make them too expensive to run when performing a specific task. However, they are used extensively in power tools and electric domestic appliances where the loss of power is not economically significant. Explain the advantages of induction motors Advantages of AC induction motors 1. Simplicity of design 2. High efficiency (hence low maintenance there are no brushes or commutators to wear out) 3. Relatively low cost William Kim HSC Physics Summary page 31 Core Topic Three From Ideas to Implementation 1. increase understandings of cathode digs led to the development of television Explain that cathode jibe resistances allowed the manipulation of a stream of charged particles Discharge Tubes Investigation of vacuum tube-shaped structures could not occur unt il good vacuum pumps had been invented.A vacuum tube is a glass tube fitted with an electrode at either end, and almost all of the air sucked out. The positive electrode is the anode The negative electrode is the cathode. When a high voltage is connected between the electrodes, an in plain ray travels from the cathode to the anode. They were called cathode rays. Cathode rays cause glass to glow green. A discharge tube is a cathode ray tube with a vacuum pump fitted, so that the air pressure inside the tube can be varied. At different air pressures, different bright effects appear in the tubes e. . bands, striations and blue spaces. These are caused by cathode rays striking atoms in the air inside the tube. The atoms become excited then release photons of visible light A beam of electrons travels from the cathode to the anode and can be deflected by electrical and/or magnetic fields. Anode film over glows here Cathode Explain why the apparent inconsistent behaviour of cathode r ays caused indicate as to whether they were charged particles or electromagnetic waves In 1892 hertz demonstrate that cathode rays could penetrate thin metal foils.This he believed supported a wave nature. In 1895 Jean-Baptise Perrin showed that cathode rays deposited negative charges on impact with an object, suggesting a particle nature. There was controversy over the nature of cathode rays waves or particles. William Kim HSC Physics Summary page 32 Identify that charged plates produce an electric field If metal plates are separated by a distance and are tie to a power source, an electric field will be produced between them. E = V/d Describe quantitatively the force acting on a charge moving through a magnetic fieldRecall that the force (F) acting on a charge (q) moving with a velocity (v) at an angle to a magnetic field (B), is given by FB = qvB Where FB = magnetic force (N) q = charge (C) v = velocity of charge (ms-1) B = magnetic field strength (T) Discuss qualitativel y the electric field strength due to a point charge, positive and negative charges and oppositely charged parallel plates. Describe quantitatively the electric field due to oppositely charged parallel plates ++++++++ If a positive charge is placed near another positive charge, it will experience a force of repulsion.A positive charge placed in a field will experience a force in the direction of the arrow. A negative charge placed in a field will experience a force opposite to the direction of the arrow. FE = qE Where FE = electric force (N) q = charge (C) E = electric field strength (NC-1) William Kim HSC Physics Summary page 33 Outline Thomsons experiment to measure the charge/mass ratio of an electron Cathode ray particles ? v? B ? ? ? ? ? ? ? FM ? ? FE ? ? ? v? E ? ? ? J. J. Thomsons Experiment By fitting plates to his CRT, he could subject the cathode rays to an electric field.The rays deflected, proving that they were charged particles, not electromagnetic waves. He obse rve that the rays deflected toward the positive plate, proving that they were negatively charged particles. By crossing electric and magnetic fields, Thomson was able to deduce the velocity of the cathode rays. By turning off the E field, the particles followed a circular arc caused by the B field. The magnetic force was acting like a centripetal force. mv qvB = r q v ? = m Br 2 ? FM = FE qvB = qE E ? v = B Thomson adjusted the strength of the fields so that the particles were not deflected.By carefully measuring the strength of the fields, Thomson could calculate v. Thomson had already measured B and worked out v. By measuring the radius of bender r, he could then calculate q/m, i. e. the charge/mass ratio of an electron. q/m for these particles was 1800 times greater than for a hydrogen ion, the simplest known atomic ion. Thomson quick compared the charges and found them to be about the same (though opposite in sign) Therefore mass for cathode ray particles was 1800 times smal ler than hydrogen Therefore cathode ray particles were subatomic particlesThis was the first discovery of subatomic particles They were later called electrons. William Kim HSC Physics Summary page 34 Outline the role in a cathode ray tube of Electrodes in the electrode gun The electric field The light concealment The Cathode Ray Tube Each CRT has a vacuum tube/chamber, a cathode, an anode, and a target. Electrodes in the electron gun The electron gun produces a narrow beam of electrons. It consists of a filament, a cathode and two open-cylinder anodes. The anodes athletic supporter to accelerate and counsel the electrons.A ring shaped electrode the grid between the cathode and anodes controls the swank of the spot by controlling the number of electrons emitted by the gun. By making the grid negative with respect to the cathode the number of electrons, and hence the brightness is reduced. The electric field Acts as a deflection system. It consists of two sets of parallel pla tes connected to a parallel plates connected to a potential difference. This produces an electric field between the plates. The Y-plates control the vertical deflection and the X-plates the horizontal deflection.The fluorescent screenland door The inside glass of the end of the tube is coated with a fluorescent material for example, zinc sulphide. When an electron beam hits the screen, the coating fluoresces and a spot of light is seen on the screen. The screen acts as a detector of cathode rays. Electrons Cathode Anode To plates and screen William Kim HSC Physics Summary page 35 Outline applications of cathode rays in oscilloscopes, electron microscopes and television sets The Cathode Ray Oscilloscope (CRO) Is an electronics diagnostics device because it can show a graph of how voltages vary over time.Deflection of the electron beam is achieved by two sets of plates. Horizontal plates cause vertical deflection while vertical plates cause horizontal deflection. TV Tube An electr on gun again produces the electron beam. Coils are used instead of plates, however. Electric current through the coils produce magnetic fields that can deflect the beams quickly from side to side, and more slowly from bottom to top. In this way the beam scans the entire screen. By varying the intensity of the beam, a picture is built up. The picture is refreshed 50 times / second, which is too fast to be noticed by the human eye.The Electron Microscope Uses electrons instead of light. Their wavelength is 100,000 times smaller than visible light, therefore their resolving power is 100,000 times greater. A sample is placed inside the chamber (which is really the CRT) The air is then sucked out An electron gun produces the electron beam Coils produce magnetic fields to focus the beam (magnetic lenses) The beam scans over the surface of the sample Detectors pick up the reflected and scattered electron beam, and from this information a 3 dimensional image is constructed Discuss the impact of increased understandings of cathode rays and the development of the oscilloscope on experimental physics The introduction of electronic control systems into all forms of science and industry has seen the cathode ray oscilloscope (CRO) become one of the most astray utilised test instruments. Because of its ability to make voltages visible, the cathode ray oscilloscope is a powerful diagnostic and development tool. William Kim HSC Physics Summary page 36 2.The reconceptualisation of the model of light led to an understanding of the photoelectric effect and black body radiation Explain qualitatively bikes experiments in measuring the speed of radio waves and how they relate to light waves Recall maxwells theory of electromagnetic waves In 1864 maxwell, through a set of four brilliant equations, predicted a range of invisible waves made up of an electric and magnetic wave that regenerate each other. The speed of these waves was reason to be 3 x 108 ms-1 and probably incl ude light.E v B Heinrich hertzs Experiment (proving Maxwells theory) Performed in 1886, wheel built equipment to generate and transmit EM waves with ? ? 1m. He also had a separate receiver (a loop of wire) located about 20m away. Spark gaps were included to show when high voltage AC was present in the transmitter or receiver. The receiver spark only appeared when the transmitter spark was present. Hertz hypothesised that the sparks set up changing electric and magnetic fields that propagated as an electromagnetic ave, as postulated by Maxwell. He showed that these were waves being transmitted because he could reflect, refract and polarise them. By measuring the frequency, he calculated v (v = f ? ) and it came out as 3 x 108 ms-1. These properties proved Maxwells theory and as they are also exhibited by light, Hertz was able to provide experimental evidence that light is a form of transverse electromagnetic wave. to induction coil 1mm gap transmitter charged plates receiver Will iam Kim HSC Physics Summary page 37 Describe Hertzs observation of the effect of a radio wave on a receiver and the photoelectric effect he produced but failed to examine Outline applications of the production of electromagnetic waves by oscillating electric charges in radio antennae Hertz observed that the transmitter spark was producing s