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Date May 2018 Marks available 1 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.

M18/4/PHYSI/SP2/ENG/TZ1/05

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.

[1]
a.

Calculate, in N, the magnitude of the magnetic force acting on the electron.

[1]
b.

Explain why the electron moves at constant speed.

[1]
c.i.

Explain why the electron moves on a circular path.

[2]
c.ii.

Markscheme

out of the page plane / ⊙

 

Do not accept just “up” or “outwards”.

[1 mark]

a.

1.60 × 10–19 × 6.8 × 105 × 8.5 = 9.2 × 10–13 «N»

[1 mark]

b.

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]

c.i.

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]

c.ii.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.i.
[N/A]
c.ii.

Syllabus sections

Core » Topic 6: Circular motion and gravitation » 6.1 – Circular motion
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