# vce physics

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VCE Physics. Unit 3 Einstein’s Relativity Revision Questions. Column 1. Column 2. The mass of an electron measured at rest. The time interval between two given events. The distance between two given events. Einstein’s Relativity Revision Question Type:. Relativity postulates. - PowerPoint PPT Presentation

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• VCE PhysicsUnit 3Einsteins RelativityRevision Questions

• Einsteins Relativity RevisionQuestion Type: According to the postulates of special relativity, certain properties are dependent on the reference frame inwhich they are observed.Q: In column 2 of the table above, indicate whether the entry in column 1 is always the same (S), or may sometimesbe different (D).SDDRelativity postulates

• Einsteins Relativity RevisionQuestion Type:Q: A Year 12 physics class is studying Einsteins special relativity.The teacher postulates a thought experiment:Imagine you are travelling at a speed of 3 108 ms-1 alongside a beam of light. What would you measure the speed of a beam of light to be?Two students put up their hands to offer an answer.Hilary says: You would measure the beam of light to be moving away from you at 3 108 ms-1.Ryan says: You would measure the beam of light to be at rest with respect to yourself: that is, its speed would be 0 ms-1.

Q: Which students answer is consistent with Einsteins special theory of relativity? Explain your reasoning.A: Hillary is correct The speed is light is invariant in all inertial frames.Light Speed Invariance

• Einsteins Relativity RevisionQuestion Type:A container inside a rocket ship is observed through a window by Sam, an astronaut, floating freely in space.Sam observes the rocket ship travelling past at a constant speed VR = 0.2 C. The dimensions of the container, as measured by astronauts inside the rocket ship, are shown in Figure 1, and are. the proper length L0 (parallel to the direction of motion of the rocket ship). the proper width W0 (perpendicular to the direction of motion of the rocket ship). the proper height H0 (perpendicular to the direction of motion of the rocket ship).Q: Which of the options (A to D) best describes its dimensions as observed by Sam?A. L < L0, W < W0 , H < H0B. L < L0, W = W0 , H = H0C. L > L0, W = W0 , H = H0D. L < L0, W < W0 , H = H0Answer:B. L < L0, W = W0 , H = H0Length Contraction

• Einsteins Relativity RevisionQuestion Type:Michelson and Morely hypothesised: if Earth moves around the Sun then it must travel though the ether. Since the medium through which light travels is the ether, there should be a difference in the measured speed of light depending on whether the light is travelling parallel to or perpendicular to the direction of Earths movement through the ether.A simplified plan of their equipment is shown in Figure 2. The apparatus was set up so that light travelling towards mirror 2 was travelling perpendicular to the motion of Earth around the Sun, and light travelling towards mirror 1 was in the direction of Earths motion in its orbit. Michelson and Morely observed a fringe pattern at the detector resulting from interference between the two light beams. The measurement was then repeated with the apparatus turned through an angle of 90, and no change was seen in the interference-fringe pattern after the rotation of the apparatus.Q: Explain the significance of this null observation.A: the speed of light is the same in both directions no motion relative to the ether no evidence to support the existence of the ether light does not need a medium there is no absolute frame of reference. The Ether

• Einsteins Relativity RevisionQuestion Type:One of the basic particles of nature is the tau meson, which can be created using beams of high energy particles from an accelerator. When created, the tau meson has a very high velocity of 0.998749 c, which means it has a Lorentz factor of 20. However it only exists for a period of 6.10 10-12 s as measured by the scientists at the accelerator laboratory. After this time it decays into two other particles. During this time it is observed to travel a distance d. Figure 3 shows the creation and decay of the tau meson in the reference frame of the scientists.Q: What is the lifetime of the tau meson as measured in its own frame of reference?A: t = to 6.10 x 10-12 s = 20(to) to = 3.05 x 10-13 sTime dilation

• Einsteins Relativity RevisionQuestion Type:When created, the tau meson has a very high velocity of 0.998749 c, which means it has a Lorentz factor of 20. However it only exists for a period of 6.10 10-12 s as measured by the scientists at the accelerator laboratory. Q: What is the distance d in Figure 3, as measured by the scientists?A: v = d/t d = v.t = (0.998749)(3 x 10-8)(6.1 x 10-12) = 1.83 x 10-3 mConstant Velocity Motion

• Einsteins Relativity RevisionQuestion Type:When created, the tau meson has a very high velocity of 0.998749 c, which means it has a Lorentz factor of 20. However it only exists for a period of 6.10 10-12 s as measured by the scientists at the accelerator laboratory. During this time it is observed to travel a distance d. Figure 3 shows the creation and decay of the tau meson in the reference frame of the scientists.Q: As measured in the reference frame of the tau meson, what would be the distance d ?A: L = Lo/ = (1.83 x 10-3)/20 = 9.15 x 10-5 mLength Contraction

• Einsteins Relativity RevisionQuestion Type:According to Einsteins special theory of relativity, mass and energy are related. The mass of an electron whenit is at rest is 9.1 10-31 kg.Q: Show that this is equivalent to an energy of 8.20 10-14 J.A: E = mc2 = (9.1 x 10-31)(3.0 x 108)2 = 8.2 x 10-14 JMass Energy Equivalence

• Einsteins Relativity RevisionQuestion Type: The electron accelerator at the ARPANSA laboratory at Yallambie, near Melbourne, can accelerate an electron to a speed such that its mass increases by a factor of 22.Q: What is the value of the Lorentz factor for an electron as it leaves the accelerator? A: Since the mass increases by 22, the Lorentz factor is 22.Lorentz Factor

• Einsteins Relativity RevisionQuestion Type:Which of the following (A to D) gives the kinetic energy of the electron as it leaves the accelerator?A. 8.20 10-15 JB. 1.72 10-12 JC. 1.80 10-13 JD. 5.11 10-6 JA: KE = mc2 moc2 = 22moc2 moc2 = 21moc2 = (21)(9.1 x 10-31)(3.0 x 108)2 = 1.72 x 10-12 J Alternative B is correctThe electron accelerator at the ARPANSA laboratory at Yallambie, near Melbourne, can accelerate an electron to a speed such that its mass increases by a factor of 22.Relativistic Kinetic Energy

• Einsteins Relativity RevisionQuestion Type:Val, Pat and Bruce are discussing the meaning of Einsteins famous equation E = mc2, when applied to an electron with mass m.Val says that an electron will transform its mass m into an amount of pure energy E, when it is travelling at the speed of light (c).Pat disagrees, and says that if it were moving at a high velocity inside a cathode ray tube it would convert its mass m into a light photon of energy E when it hits the glass face.Bruce, on the other hand, thinks that just by its existence, the electron of mass m has an energy of E.Q: Write the name of the student with the best explanation of the equation.A: BruceMass Energy Equivalence

• Einsteins Relativity RevisionQuestion Type: In 1861 James Clerk Maxwell proved that light was an electromagnetic wave with a speed of 3 108 ms1. Following Maxwells predictions, physicists had some concerns.Q: Which one or more of the statements (A to D) below outlines one of these concerns?A. All waves propagate in a medium, but there was no medium in empty space.B. Unlike the speed of other waves, experiments showed that the speed of light did not depend on the observer or source speed.C. If light was a wave, it would not diffract.D. The speed of light predicted by Maxwell did not agree with the measured speed.A: Alternatives A & BHistory of Relativity

• Einsteins Relativity RevisionQuestion Type:Imagine two students travelling in a spaceship toward the Sun at speed v (Figure 1). They plan to measure the speed of light in two experiments, as a test of the prediction of James Clerk Maxwell and that of Galilean relativity.In the first experiment, they determine the speed of light (c) within the rocket ship by measuring the time for a short pulse of light emitted from a flashbulb at point A to reach point B. They got the accepted value for c. In the second experiment they determined the speed of light for a beam of light from the Sun, which passed through a porthole in the rocket nose. This was done by measuring the time for the light to travel between point A and point B.

• Einsteins Relativity RevisionQuestion Type: Q: Which one of the following statements (A to D) is consistent with the predictions of Maxwell, and of Galilean relativity, concerning the value of the speed of light obtained in this second measurement?A. Both predict the speed to be c.B. Maxwells theory predicts the speed to be c, while Galilean relativity predicts a value of (c + v).C. Maxwells theory predicts a speed of (c + v), while Galilean relativity predicts a value of c.D. Both predict the speed to be (c + v).A: Alternative BIn the second experiment they determined the speed of light for a beam of light from the Sun, which passed through a porthole in the rocket nose. This was done by measuring the time for the light to travel between point A and point B.Light Speed Invariance

• Einsteins Relativity RevisionQuestion Type:In an experiment done at Massachusetts Institute of Technology, electrons were given a series of known kinetic energies (KE) by accelerating them across a range of electric potentials, and measuring the electrons velocity, v, for each value of KEThe solid curve in Figure 2 shows the variation of v2 as a function of KE, as measured in the experiment. The dashed curve is the value of v2 calculated using the Newtonian

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