Lesson 8.3.3

8.3.3 Relativistic effects and high-energy physics Quiz: Pearson Edexcel Physics, Unit 8

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 8.3.3, Relativistic effects and high-energy physics: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 8: Nuclear and Particle Physics, written with Revision Ninja.

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The 20 questions

  1. What relativistic effect makes a fast-moving particle appear to live longer than the same particle at rest?

    • Mass decrease, so the particle loses energy and decays more slowly
    • Charge increase, so the particle is stabilised by its greater electric field
    • Length contraction, so the particle's lifetime is shorter when it moves quickly
    • Time dilation, so the lifetime measured in the laboratory is longer when the particle moves quickly

  2. In which frame is the shortest lifetime of a particle measured?

    • The frame in which the particle has its greatest kinetic energy
    • The frame of the laboratory in which the particle is moving fastest
    • The frame of an observer moving in the same direction at a higher speed
    • The frame in which the particle is at rest

  3. What happens to the energy needed to accelerate a particle as its speed approaches the speed of light in a vacuum?

    • It increases without limit, so the particle can never reach the speed of light
    • It decreases steadily until the particle reaches the speed of light
    • It stays constant, so particles can reach the speed of light easily
    • It becomes zero at the speed of light because the particle has no mass

  4. Why do cosmic-ray muons created high in the atmosphere reach the ground in significant numbers?

    • Their lifetime is infinite, so they never decay during the journey
    • Their high speed makes their lifetime appear longer to observers on the ground, so they survive the journey
    • Air molecules stop them from decaying, so they arrive at the ground intact
    • They are attracted to the ground by the Earth's magnetic field, which shortens the journey

  5. Why are high energies required to investigate the structure of nucleons?

    • Higher energies make nucleons heavier, so their structure is easier to see
    • Higher energies allow nucleons to lose their charge so they can be deflected
    • Higher energies allow particles to probe smaller distances within the nucleon
    • Higher energies allow the nucleons to become larger and easier to observe

  6. A muon has a rest lifetime of 2.2 microseconds and travels at 3.0 x 10^8 m s^-1. Ignoring relativistic effects, what distance would it travel in one rest lifetime?

    • About 0.66 m
    • About 66 m
    • About 660 m
    • About 6600 m

  7. Two identical muons have the same rest lifetime. One is at rest in the laboratory and the other moves at high speed. Which has the longer lifetime as measured in the laboratory?

    • The fast-moving muon, because of time dilation
    • The muon at rest, because it has no kinetic energy to lose
    • The muon at rest, because the fast muon decays more quickly from kinetic energy
    • They have the same lifetime, because lifetimes never depend on motion

  8. Which measurement would best test time dilation for muons?

    • Counting the number of electrons produced when muons are absorbed by lead
    • Recording the colour of light emitted when a muon passes through air
    • Measuring the mass of muons that are at rest in a detector
    • Comparing the decay rate of muons at rest with that of muons moving at high speed

  9. A particle accelerator increases the energy of a proton from 10 GeV to 100 GeV. What happens to the speed of the proton?

    • It falls to zero, because the proton becomes heavier
    • It changes very little, remaining extremely close to the speed of light
    • It increases by the same factor as the energy
    • It doubles, because the energy has been multiplied by ten

  10. Why does the long lifetime of some high-energy particles matter for detector design?

    • Long-lived particles stop before reaching any detector, so detectors are not needed for them
    • Long-lived particles change into neutrons, which are then recorded by the detector
    • Long-lived particles travel measurable distances before decaying, so their tracks can be recorded and analysed
    • Long-lived particles emit light constantly, so detectors must block that light

  11. Which statement describes a relativistic effect correctly?

    • It becomes significant only for uncharged particles at rest
    • It becomes significant only at everyday walking speeds
    • It is independent of speed and is observed for every particle in the universe
    • It becomes significant when speeds are a substantial fraction of the speed of light

  12. A muon reaches the ground after travelling about 6.6 km, which is a distance measured in the laboratory. The laboratory measured lifetime is 22 microseconds, and the speed is near 3.0 x 10^8 m s^-1. What does this show?

    • The muon's speed is actually much slower than the speed of light
    • The muon's rest lifetime has changed to 22 microseconds in its own frame
    • The muon has been reflected by the atmosphere, which is why it travels far
    • The muon's lifetime is extended by time dilation, so it survives long enough to travel this distance

  13. Why do observers in different frames disagree about the lifetime of a moving muon?

    • Observers always agree on the lifetime, but disagree on the speed of the muon
    • The muon changes its rest mass depending on who is measuring it
    • The muon's lifetime depends on the colour of light used to observe it
    • Time intervals depend on the relative motion of the observer and the muon, so each frame measures a different duration

  14. A student claims that particles moving at high speed have shorter lifetimes because they are more energetic. Which response is correct?

    • The student is wrong because particles never decay at all when they are moving
    • The student is right: more energetic particles always decay more quickly
    • The student is right, but only for particles that carry electric charge
    • The student is wrong: relativistic effects extend the lifetime measured in the laboratory frame for fast-moving particles

  15. Which statement about relativistic effects in high-energy physics is correct?

    • They can always be ignored, because classical predictions are accurate at all speeds
    • They apply only to the rest mass of particles and never to their lifetimes
    • They must be included when speeds approach the speed of light, or predictions for lifetimes and energies will be wrong
    • They only matter for macroscopic objects, and never for subatomic particles

  16. A muon has a rest lifetime of 2.2 microseconds and moves at 0.50c. Ignoring relativistic effects, how far does it travel in one rest lifetime?

    • About 3300 m
    • About 660 m
    • About 33 m
    • About 330 m

  17. A muon moves at 0.99c. Relativistic effects are ignored in a naive calculation. What is the main error this causes in predicting how far the muon travels before decaying?

    • The predicted distance is far too short, because the lab lifetime is much longer than the rest lifetime
    • The predicted distance is correct, because relativistic effects only change the muon's mass
    • The predicted distance is too short only at speeds below half the speed of light
    • The predicted distance is far too long, because the muon speeds up when it decays

  18. A cosmic-ray muon with rest lifetime 2.2 microseconds is observed in the laboratory to last 22 microseconds. Roughly what is the ratio of the lab lifetime to the rest lifetime?

    • About 10
    • About 100
    • About 0.1
    • About 2

  19. Which quantity is measured as longer by a laboratory observer than by an observer moving with a particle?

    • The speed of light in the particle's rest frame
    • The charge carried by the particle
    • The time interval between the creation and decay of the particle
    • The rest mass of the particle

  20. A muon moving at 0.99c has its lab lifetime compared with its rest lifetime. Which statement is correct?

    • The lab lifetime is shorter than the rest lifetime because the muon is moving
    • The lab lifetime is equal to the rest lifetime at any speed
    • The lab lifetime is unchanged, because only the muon's energy changes at high speed
    • The lab lifetime is many times longer than the rest lifetime

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