Electric force between point charges: past paper questions
Real questions on electric force between point charges
The newest 20 of 55 written questions. Open one to see it on the real paper.
- 9702/41 · May/June 2025 · Q7a[2]
Define magnetic flux density.
See it on the paper → - 9702/41 · May/June 2025 · Q7b(i)[1]
State an expression, in terms of some or all of m, Q, B and v, for the magnetic force F that acts on the particle when it is at point Y. F =
See it on the paper → - 9702/41 · May/June 2025 · Q7b(ii)[1]
On Fig. 7.1, draw an arrow at point Y to indicate the direction of the force in (b)(i).
See it on the paper → - 9702/41 · May/June 2025 · Q7b(iii)[1]
On Fig. 7.1, draw a line to show a possible path for the particle through the region of the magnetic field.
See it on the paper → - 9702/41 · May/June 2025 · Q7c(i)[3]
Explain how an electric field can be used with the magnetic field to ensure that the particle in (b) now passes through point Z.
See it on the paper → - 9702/41 · May/June 2025 · Q7c(ii)[2]
Derive an expression for v in terms of B and the electric field strength E. v =
See it on the paper → - 9702/43 · May/June 2025 · Q2a[2]
State Coulomb’s law.
See it on the paper → - 9702/43 · May/June 2025 · Q2b(ii)[1]
Show that the electric force between the nucleus and one of the electrons is 1.6 × 10 –8 N.
See it on the paper → - 9702/43 · May/June 2025 · Q2c(i)[2]
Calculate the speed of the orbiting electrons. speed = m s –1
See it on the paper → - 9702/43 · May/June 2025 · Q7b(i)[1]
State an expression, in terms of some or all of m, Q, B and v, for the magnetic force F that acts on the particle when it is at point Y. F =
See it on the paper → - 9702/43 · May/June 2025 · Q7b(ii)[1]
On Fig. 7.1, draw an arrow at point Y to indicate the direction of the force in (b)(i).
See it on the paper → - 9702/43 · May/June 2025 · Q7b(iii)[1]
On Fig. 7.1, draw a line to show a possible path for the particle through the region of the magnetic field.
See it on the paper → - 9702/42 · October/November 2024 · Q6a[2]
State Coulomb’s law.
See it on the paper → - 9702/42 · October/November 2023 · Q2e[1]
The surface of the Moon reaches temperatures of approximately 400 K when in direct sunlight. Use your answers in (c) and (d) to suggest a reason why the Moon does not have an atmosphere consisting of hydrogen.
See it on the paper → - 9702/42 · October/November 2023 · Q5a[2]
State Coulomb’s law.
See it on the paper → - 9702/43 · October/November 2023 · Q6b(iv)[3]
Use the information in (b)(ii) to calculate the distance d between the path of the electrons entering the magnetic field and the path of the electrons leaving it. d = m
See it on the paper → - 9702/43 · October/November 2023 · Q6c[3]
The electrons in (b) are replaced with positrons that are moving with speed 3.4 × 10 7 m s –1 along the same initial path as the electrons. The positrons enter the magnetic field at point X on Fig. 6.1. On Fig. 6.1, draw a line to show the path of the positrons through the magnetic field.
See it on the paper → - 9702/42 · February/March 2023 · Q4c(iii)[1]
Explain why the electron does not follow a circular path.
See it on the paper → - 9702/43 · October/November 2022 · Q4c(ii)[3]
A helium nucleus ( 42 He) now enters the region of the electric field along the same initial path as the proton and travelling at the same initial speed. State and explain how the final speed of the helium nucleus compares with the final speed of the proton after leaving the region of the electric field.
See it on the paper → - 9702/42 · May/June 2022 · Q2a[2]
State Coulomb’s law.
See it on the paper →
What examiners said
This was another challenging question. Even many of the stronger candidates missed the point that, even though the r.m.s. speed of the molecules is a little less than the escape speed, there is a distribution of molecular speeds in which the r.m.s. value is only an average. As a result, many of the molecules do have the speed required to escape, and over time all will do so. Many responses did not...
— Examiner report, October/November 2023, 9702/42 Q2(e) (Cambridge)
This question was well answered, with most candidates able to give a correct statement of Coulomb’s law.
— Examiner report, October/November 2023, 9702/42 Q5(a) (Cambridge)
A large number of candidates knew the equations to use here. The most common errors were firstly to quote an answer to only one significant figure (0.04 m) where two significant figures were needed, and secondly to determine the radius but then not double it to give the diameter d of the circular path.
— Examiner report, October/November 2023, 9702/43 Q6(b)(iv) (Cambridge)
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