Lesson 8.2.1

8.2.1 Thermionic emission and charged particles in accelerators Quiz: Pearson Edexcel Physics, Unit 8

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

In partnership with Revision Ninja

Lesson 8.2.1, Thermionic emission and charged particles in accelerators: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 8: Nuclear and Particle Physics, written with Revision Ninja.

Host it live on the board and students join with a game code on their own devices, or revise alone with Free Play. The answers are revealed in the game.

Host this setFree Play

The 20 questions

  1. What is thermionic emission?

    • The emission of electrons from the surface of a heated metal
    • The absorption of electrons by a metal when it is cooled to low temperature
    • The emission of photons from the surface of a metal exposed to ultraviolet light
    • The emission of alpha particles from an unstable nucleus when heated

  2. Why does heating a metal cause electrons to be emitted from its surface?

    • The heat causes the metal to become magnetic, which attracts electrons out of the surface
    • Heat converts the metal's neutrons into free electrons that leave the surface
    • The thermal energy given to the electrons is enough for them to overcome the forces holding them in the metal
    • Heating reduces the mass of the electrons, so they can escape from the surface

  3. In a linear accelerator, what is the purpose of the drift tubes?

    • They shield the particles while the alternating field reverses, so particles are accelerated only in the gaps between tubes
    • They detect the particles and record their energies as they leave the machine
    • They focus the particles into a narrow beam using a magnetic field
    • They produce the alternating voltage that accelerates the particles

  4. In a cyclotron, what keeps the charged particles moving in a circular path?

    • The gravitational attraction of the Earth towards the centre of the machine
    • A uniform electric field that acts along the direction of motion
    • A uniform magnetic field perpendicular to the plane of the path
    • The pressure of a gas that surrounds the particles inside the machine

  5. In a cyclotron, what accelerates the charged particles each time they cross the gap between the dees?

    • The gravitational force that pulls the particles towards the gap
    • A steady magnetic field that increases in strength over time
    • An alternating electric potential difference across the gap
    • The magnetic field, which does work on the particles in the gap

  6. What is the radius of the circular path of a charged particle of momentum p and charge Q in a magnetic field B?

    • r = p / (B Q^2)
    • r = BQ / p
    • r = p B / Q
    • r = p / (BQ)

  7. An electron leaves a hot cathode from rest and is accelerated through 2000 V. What is its speed? The electron mass is 9.11 x 10^-31 kg.

    • 2.7 x 10^7 m s^-1
    • 6.3 x 10^5 m s^-1
    • 1.9 x 10^7 m s^-1
    • 5.3 x 10^7 m s^-1

  8. An electron leaves a hot cathode from rest and is accelerated through 500 V. What kinetic energy does it gain, in joules?

    • 8.0 x 10^-17 J
    • 5.0 x 10^2 J
    • 3.1 x 10^-19 J
    • 8.0 x 10^-16 J

  9. A proton of mass 1.67 x 10^-27 kg moves at 1.0 x 10^6 m s^-1 perpendicular to a magnetic field of flux density 0.50 T. What is the radius of its path?

    • 2.1 x 10^2 m
    • 4.2 x 10^-2 m
    • 1.0 x 10^-2 m
    • 2.1 x 10^-2 m

  10. An electron moves in a circular path in a uniform magnetic field of flux density 0.10 T. What is the time for one complete revolution? The electron mass is 9.11 x 10^-31 kg.

    • 3.6 x 10^-8 s
    • 7.2 x 10^-10 s
    • 1.8 x 10^-10 s
    • 3.6 x 10^-10 s

  11. A cyclotron operates with a fixed magnetic field. If the magnetic flux density is doubled, what must happen to the frequency of the accelerating potential?

    • It must quadruple, because the frequency depends on the square of the field
    • It must stay the same, because the frequency depends only on the particle mass
    • It must halve, to match the new cyclotron frequency of the particles
    • It must double, to match the new cyclotron frequency of the particles

  12. Why are the lengths of successive drift tubes in a linear accelerator made progressively longer?

    • The tubes must be longer to produce a stronger magnetic field at the far end of the machine
    • The mass of the particles increases along the tube, so longer tubes are needed to hold them
    • The field strength decreases along the tube, so longer tubes are needed to keep the field constant
    • As the particles speed up, each tube must be longer so that the particle spends half a field period inside it

  13. What determines the kinetic energy gained by a charged particle accelerated through a potential difference V?

    • The square of its charge divided by the potential difference, so Ek = Q^2 / V
    • The potential difference divided by its charge, so Ek = V / Q
    • The product of its charge and the potential difference, so Ek = QV
    • The product of its mass and the potential difference, so Ek = mV

  14. An electron of speed 5.0 x 10^6 m s^-1 enters a uniform magnetic field of flux density 0.020 T perpendicular to the field. What is the radius of its circular path?

    • 1.4 x 10^-3 m
    • 7.0 x 10^-4 m
    • 2.8 x 10^-3 m
    • 1.4 x 10^-6 m

  15. A proton and an alpha particle are accelerated from rest through the same potential difference and then enter the same uniform magnetic field perpendicular to it. What is the ratio of the alpha particle radius to the proton radius?

    • sqrt(2), about 1.4
    • 2.0
    • 0.50
    • 4.0

  16. The simple cyclotron analysis treats the particle mass as constant. Under what condition is this approximation acceptable?

    • When the particle speeds are much less than the speed of light
    • When the particle is always stationary in the magnetic field
    • When the magnetic flux density is zero throughout the machine
    • When the particles are electrons rather than protons or alpha particles

  17. In a magnetic field, a positive particle and a negative particle enter with the same velocity. How do their paths compare?

    • Neither is deflected because the field acts only on uncharged particles
    • They are deflected in opposite directions
    • They are deflected in the same direction, but the negative particle is deflected more
    • They are deflected in the same direction because the field acts on the mass

  18. Why does ionisation of gas atoms along a particle's path help detect the particle?

    • Ionisation converts the particle into a neutral atom that the detector can count
    • The ionised gas becomes a superconductor and blocks the particle from moving
    • The ions and free electrons left behind form a trail that can be registered and recorded by the detector
    • The ions emit light that cancels out the particle's energy and stops it

  19. A linear accelerator is driven by an alternating voltage of frequency 100 MHz. For how long is each half-cycle of the voltage?

    • 0.010 microseconds
    • 10 ns
    • 2.5 ns
    • 5.0 ns

  20. A student says a cyclotron can accelerate particles indefinitely to any speed because the magnetic field keeps them moving in a circle. Which response is correct?

    • The student is right: the magnetic field supplies the energy that keeps increasing the speed of the particles
    • The student is right, because the magnetic field stores energy that is released as the particle speeds up
    • The student is wrong: magnetic fields do no work, so energy comes from the electric field across the gap
    • The student is wrong because particles in a cyclotron are never accelerated at all

All Pearson Edexcel Physics quizzes