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Special relativity (A-level only)

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Question 5

An electrostatic linear accelerator (LINAC) is used to study the relativistic properties of high-speed protons. A pulsed beam of protons is accelerated from rest through a total potential difference (pd) of 480 MV480 \text{ MV}480 MV and directed towards a graphite block detector.

a.

Show that each proton gains approximately 7.7×10−11 J7.7 \times 10^{-11} \text{ J}7.7×10−11 J of kinetic energy.

[1]
b.

The pulse of protons causes the temperature of a 1.20 kg1.20 \text{ kg}1.20 kg graphite block to increase by 4.06 K4.06 \text{ K}4.06 K. The total number of protons in the pulse is 4.50×10134.50 \times 10^{13}4.50×1013.

Deduce whether this observed temperature increase is consistent with an accelerating pd of 480 MV480 \text{ MV}480 MV.

  • specific heat capacity of graphite = 710 J kg−1 K−1710 \text{ J kg}^{-1} \text{ K}^{-1}710 J kg−1 K−1
[2]
c.

The speed of the protons between the accelerator's final stage and the detector block is measured to be 2.25×108 m s−12.25 \times 10^8 \text{ m s}^{-1}2.25×108 m s−1.

  • Student A suggests that the non-relativistic equation for kinetic energy can be used here.
  • Student B suggests that the relativistic equation for kinetic energy is required.

Evaluate both suggestions using calculations of the kinetic energy of a proton at this speed.

  • mass of proton mp=1.67×10−27 kgm_p = 1.67 \times 10^{-27} \text{ kg}mp​=1.67×10−27 kg
  • speed of light c=3.00×108 m s−1c = 3.00 \times 10^8 \text{ m s}^{-1}c=3.00×108 m s−1
[4]
d.

A laboratory timer records the time taken for the proton pulse to travel from the final collimator to the graphite block as 12.0 ns12.0 \text{ ns}12.0 ns.

What is the proper time interval for a proton travelling this distance?

  • <12.0 ns< 12.0 \text{ ns}<12.0 ns
  • 12.0 ns12.0 \text{ ns}12.0 ns
  • >12.0 ns> 12.0 \text{ ns}>12.0 ns
[1]
e.

The protons were accelerated from rest in 161616 stages, each using a pd of 30 MV30 \text{ MV}30 MV.

Compare, for a proton:

  • its increase in kinetic energy for the first stage compared to the 16th stage
  • its increase in speed for the first stage compared to the 16th stage

Justify your answer. No further calculations are required.

[4]

Special relativity (A-level only) Questions

  1. A Level
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  3. /Special relativity (A-level only)