| Date | May 2014 | Marks available | 2 | Reference code | 14M.3.SL.TZ1.19 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Question number | 19 | Adapted from | N/A |
Question
This question is about the nature and properties of electromagnetic waves.
Electromagnetic waves propagating in a medium suffer dispersion. Describe what is meant by dispersion.
A charge moves backwards and forwards along a wire, as shown in the diagram below.
Outline, with reference to the motion of the charge, why electromagnetic radiation is produced by the moving charge.
Markscheme
waves of different wavelength/frequency;
travel at different velocities;
the index of refraction of the medium depends on the wavelength/frequency;
during simple harmonic motion the charge oscillates/accelerates;
(oscillating/accelerating) charges radiate/produce (varying) electric/magnetic fields / produce electromagnetic waves;
Examiners report
Too many candidates showed that they do not know the terminology and vaguely described other phenomena instead of dispersion, quite often scattering. Breaking into component colours was sometimes mentioned by the candidates but this was not accepted as correct as the question was about electromagnetic waves, not only about light. A reasonable number of correct answers were seen with reference of both different speed and index of refraction.
In (b) only the stronger HL candidates clearly connected accelerated charge with the production of electromagnetic radiation. Most SL answers simply repeated the production of electromagnetic waves, missing the importance of the acceleration of the electron and not relating it to electric and magnetic fields.
