| Date | November 2019 | Marks available | 2 | Reference code | 19N.3.SL.TZ0.3 |
| Level | Standard level | Paper | Paper 3 | Time zone | 0 - no time zone |
| Command term | Deduce | Question number | 3 | Adapted from | N/A |
Question
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.
One of the two postulates of special relativity states that the speed of light in a vacuum is the same for all observers in inertial reference frames. State the other postulate of special relativity.
State the nature of the force on the particle P in the reference frame of the laboratory.
Deduce, using your answer to part (a), the nature of the force that acts on the particle P in the rest frame of P.
Explain how the force in part (b)(ii) arises.
The velocity of P is 0.30c relative to the laboratory. A second particle Q moves at a velocity of 0.80c relative to the laboratory.
Calculate the speed of Q relative to P.
Markscheme
laws of physics are the same for all observers
OR
laws of physics are the same in all «inertial» frames ✔
NOTE: OWTTE
magnetic ✔
«from 3a»
force must still be repulsive ✔
for P there is no magnetic force AND force is electric/electrostatic
OR
since P is at rest the force is electric/electrostatic ✔
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.
✔
✔
NOTE: Accept 0.89c if all negative values used. Accept –0.89c even though speed is required.
Examiners report
Syllabus sections
- 17N.3.SL.TZ0.4: Outline the conclusion from Maxwell’s work on electromagnetism that led to one of...
- 19M.3.SL.TZ1.3b: State the speed of the flash of light according to an observer on the ground using Maxwell’s...
- 19M.3.SL.TZ1.3a: State the speed of the flash of light according to an observer on the ground using Galilean...
-
18M.3.SL.TZ1.4a.i:
Calculate, according to Galilean relativity, the time taken for a muon to travel to the ground.
-
18M.3.SL.TZ2.3a.i:
Calculate, for the reference frame of rocket A, the speed of rocket B according to the Galilean transformation.
-
17M.3.SL.TZ2.3b:
A current is established in a long straight wire that is at rest in a laboratory.
A proton is at rest relative to the laboratory and the wire.
Observer X is at rest in the laboratory. Observer Y moves to the right with constant speed relative to the laboratory. Compare and contrast how observer X and observer Y account for any non-gravitational forces on the proton.
-
17M.3.SL.TZ2.3a:
State one prediction of Maxwell’s theory of electromagnetism that is consistent with special relativity.
-
18N.3.SL.TZ0.4b.i:
Determine the time it takes the probe to reach the front of the rocket according to an observer at rest in the rocket.
-
18N.3.SL.TZ0.3b.ii:
hence show that the space coordinate of E in frame S is .
- 18N.3.SL.TZ0.3a: State what is meant by a reference frame.
-
18M.3.SL.TZ1.3b.ii:
Deduce whether the overall field around the wire is electric, magnetic or a combination of both according to observer Y.
-
17M.3.SL.TZ1.3a:
State what is meant by a reference frame.
-
17M.3.SL.TZ1.3b.ii:
State and explain whether the force experienced by P is magnetic, electric or both, in the rest frame of P.
- 16N.3.SL.TZ0.4a: Define frame of reference.
- 19N.3.SL.TZ0.3b(i): State the nature of the force on the particle P in the reference frame of the laboratory.
-
19N.3.SL.TZ0.3b(iii):
Explain how the force in part (b)(ii) arises.
-
17M.3.SL.TZ1.3b.i:
State and explain whether the force experienced by P is magnetic, electric or both, in reference frame S.
-
19M.3.SL.TZ1.4a.i:
Estimate in the Earth frame the fraction of the original muons that will reach the Earth’s surface before decaying according to Newtonian mechanics.
-
18M.3.SL.TZ1.3a:
State whether the field around the wire according to observer X is electric, magnetic or a combination of both.
-
18N.3.SL.TZ0.3b.i:
explain why the time coordinate of E in frame S is .
- 20N.3.SL.TZ0.3b: State a postulate that is the same for both special relativity and Galilean relativity.
- 20N.3.SL.TZ0.3c(i): Identify the nature of the attractive force recorded by an observer stationary with respect...
- 20N.3.SL.TZ0.4a: The Lorentz transformations assume that the speed of light is constant. Outline what the...
- 20N.3.SL.TZ0.3a: Maxwell’s equations led to the constancy of the speed of light. Identify what Maxwell’s...
- 20N.3.SL.TZ0.3c(ii): A second observer moves at the drift velocity of the electron current in the wires. Discuss...
-
16N.3.SL.TZ0.4b:
In the reference frame of the laboratory the force on X is magnetic.
(i) State the nature of the force acting on X in this reference frame where X is at rest.
(ii) Explain how this force arises.
- 19M.3.SL.TZ2.5b: Explain why there is no magnetic force on each proton in its own rest frame.
- 19M.3.SL.TZ2.5c: Explain why there must be a resultant repulsive force on the protons in all reference frames.
- 19M.3.SL.TZ2.4ai: Define an inertial reference frame.
- 19M.3.SL.TZ2.4aii: As the spaceship passes the Earth it emits a flash of light that travels in the same...
-
19M.3.SL.TZ2.4b:
Use your answer to (a)(ii) to describe the paradigm shift that Einstein’s theory of special relativity produced.
- 19M.3.SL.TZ2.5a: Outline why there is an attractive magnetic force on each proton in the laboratory frame.
-
18M.3.SL.TZ1.4a.ii:
Deduce why only a small fraction of the total number of muons created is expected to be detected at ground level according to Galilean relativity.
