| Date | May 2018 | Marks available | 2 | Reference code | 18M.2.SL.TZ1.5 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 5 | Adapted from | N/A |
Question
An electron moves in circular motion in a uniform magnetic field.
The velocity of the electron at point P is 6.8 × 105 m s–1 in the direction shown.
The magnitude of the magnetic field is 8.5 T.
State the direction of the magnetic field.
Calculate, in N, the magnitude of the magnetic force acting on the electron.
Explain why the electron moves at constant speed.
Explain why the electron moves on a circular path.
Markscheme
out of the page plane / ⊙
Do not accept just “up” or “outwards”.
[1 mark]
1.60 × 10–19 × 6.8 × 105 × 8.5 = 9.2 × 10–13 «N»
[1 mark]
the magnetic force does not do work on the electron hence does not change the electron’s kinetic energy
OR
the magnetic force/acceleration is at right angles to velocity
[1 mark]
the velocity of the electron is at right angles to the magnetic field
(therefore) there is a centripetal acceleration / force acting on the charge
OWTTE
[2 marks]
