DP Physics (last assessment 2024)
Question 19N.3.SL.TZ0.b(iii)
| Date | November 2019 | Marks available | [Maximum mark: 2] | Reference code | 19N.3.SL.TZ0.b(iii) |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | b(iii) | Adapted from | N/A |
b(iii).
[Maximum mark: 2]
19N.3.SL.TZ0.b(iii)
A long straight current-carrying wire is at rest in a laboratory. A negatively-charged particle P outside the wire moves parallel to the current with constant velocity v relative to the laboratory.
In the reference frame of the laboratory the particle P experiences a repulsive force away from the wire.
Explain how the force in part (b)(ii) arises.
[2]
Markscheme
protons and electrons in the wire move with different velocities «relative to P»
OR
speed of electrons is greater ✔
«for P» the density of protons and electrons in wire will be different «due to length contraction»
OR
«for P» the wire appears to have negative charge «due to length contraction» ✔
«hence electric force arises»
NOTE: Do not award mark for mention of length contraction without details.
