| Date | November 2020 | Marks available | 1 | Reference code | 20N.3.SL.TZ0.4 |
| Level | Standard level | Paper | Paper 3 | Time zone | 0 - no time zone |
| Command term | Outline | Question number | 4 | Adapted from | N/A |
Question
A spaceship is travelling at , away from Earth. It launches a probe away from Earth, at relative to the spaceship. An observer on the probe measures the length of the probe to be .
The Lorentz transformations assume that the speed of light is constant. Outline what the Galilean transformations assume.
Deduce the length of the probe as measured by an observer in the spaceship.
Explain which of the lengths is the proper length.
Calculate the speed of the probe in terms of , relative to Earth.
Markscheme
constancy of time
OR
speed of light > c is possible ✓
OWTTE
✓
length = ✓
Allow length in the range to .
Allow ECF from wrong
Award [2] marks for a bald correct answer in the range indicated above.
/ measurement made on the probe ✓
the measurement made by an observer at rest in the frame of the probe ✓
✓
✓
Allow all negative signs for velocities
Award [2] marks for a bald correct answer
Examiners report
Although the expected answers was the constancy of time, the markscheme allowed references to the speed of light not being constant, as this was a common answer, deriving from the stem used in the question.
Very well answered.
"In the same frame" does not highlight the need to be "at rest" in that frame, and was the most frequent wrong answer, although a vast majority scored full marks here.
Very well answered.
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(ii):
Deduce, using your answer to part (a), the nature of the force that acts on the particle P in the rest frame of P.
-
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.TZ0.3a: 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.
