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Date May 2018 Marks available 2 Reference code 18M.3.SL.TZ1.3
Level Standard level Paper Paper 3 Time zone Time zone 1
Command term Discuss Question number 3 Adapted from N/A

Question

The diagram shows the motion of the electrons in a metal wire carrying an electric current as seen by an observer X at rest with respect to the wire. The distance between adjacent positive charges is d.

M18/4/PHYSI/SP3/ENG/TZ1/03

Observer Y is at rest with respect to the electrons.

State whether the field around the wire according to observer X is electric, magnetic or a combination of both.

[1]
a.

Discuss the change in d according to observer Y.

[2]
b.i.

Deduce whether the overall field around the wire is electric, magnetic or a combination of both according to observer Y.

[2]
b.ii.

Markscheme

magnetic field

[1 mark]

a.

«according to Y» the positive charges are moving «to the right»

d decreases

 

For MP1, movement of positive charges must be mentioned explicitly.

[2 marks]

b.i.

positive charges are moving, so there is a magnetic field

the density of positive charges is higher than that of negative charges, so there is an electric field

 

The reason must be given for each point to be awarded.

[2 marks]

b.ii.

Examiners report

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

Syllabus sections

Option A: Relativity » Option A: Relativity (Core topics) » A.2 – Lorentz transformations
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