Question 20N.3.SL.TZ0.3
| Date | November 2020 | Marks available | [Maximum mark: 6] | Reference code | 20N.3.SL.TZ0.3 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Discuss, Identify, State | Question number | 3 | Adapted from | N/A |
Maxwell’s equations led to the constancy of the speed of light. Identify what Maxwell’s equations describe.
[1]
mention of electric AND magnetic fields ✓
OR
mention of electromagnetic radiation/wave/fields ✓
Easy introduction fairly well answered by most candidates.
State a postulate that is the same for both special relativity and Galilean relativity.
[1]
the laws of physics are the same in all «inertial» frames of reference/for all «inertial» observers ✓
OWTTE
With a few exceptions referring to Newton's first, this was very well answered.
Two parallel current-carrying wires have equal currents in the same direction. There is an attractive force between the wires.
Identify the nature of the attractive force recorded by an observer stationary with respect to the wires.
[1]
magnetic ✓
Most scored by recognizing the force as magnetic.
A second observer moves at the drift velocity of the electron current in the wires. Discuss how this observer accounts for the force between the wires.
[3]
«In observer frame» protons «in the two wires» move in same/parallel direction ✓
these moving protons produce magnetic attraction ✓
there is also a smaller electrostatic repulsion due to wires appearing positive due to length contraction «of proton spacing» ✓
OWTTE
Many failed to recognize that the magnetic force would still be present due to the current produced by the relative motion of the protons in both wires, and only focused on the repulsive electrostatic due to length contraction.
