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Date May 2017 Marks available 1 Reference code 17M.3.SL.TZ1.3
Level Standard level Paper Paper 3 Time zone Time zone 1
Command term State Question number 3 Adapted from N/A

Question

A long current-carrying wire is at rest in the reference frame S of the laboratory. A positively charged particle P outside the wire moves with velocity v relative to S. The electrons making up the current in the wire move with the same velocity v relative to S.

State what is meant by a reference frame.

[1]
a.

State and explain whether the force experienced by P is magnetic, electric or both, in reference frame S.

[2]
b.i.

State and explain whether the force experienced by P is magnetic, electric or both, in the rest frame of P.

[3]
b.ii.

Markscheme

a set of coordinate axes and clocks used to measure the position «in space/time of an object at a particular time»
OR
a coordinate system to measure x,y,z, and t / OWTTE

[1 mark]

a.

magnetic only

there is a current but no «net» charge «in the wire»

[2 marks]

b.i.

electric only

P is stationary so experiences no magnetic force

relativistic contraction will increase the density of protons in the wire

[3 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.1 – The beginnings of relativity

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