| Date | May 2017 | Marks available | 3 | Reference code | 17M.3.SL.TZ1.3 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | State and Explain | 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.
State and explain whether the force experienced by P is magnetic, electric or both, in reference frame S.
State and explain whether the force experienced by P is magnetic, electric or both, in the rest frame of P.
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]
magnetic only
there is a current but no «net» charge «in the wire»
[2 marks]
electric only
P is stationary so experiences no magnetic force
relativistic contraction will increase the density of protons in the wire
[3 marks]
