Explain how these maxima and minima are formed.

(i)     wavelength of the microwaves.

(ii)     frequency of the microwaves.

Describe and explain how it could be demonstrated that the microwaves are polarized.

standing wave formed;

by superposition/interference of (forward) wave and reflected wave;

maximum where interference is constructive / minimum where interference is destructive;

maxima where waves in phase;

minima where waves are completely/180°/\(\pi \)/half wavelength out of phase;

(i)     \({\text{130 mm}} \equiv {\text{9 half wavelengths}}\);

29 mm;

(ii)     \(f = \frac{c}{\lambda }\);

\( = 10{\text{ GHz}}\);

place a metal grid/analyser between source and detector;

electric field vector (of the microwaves) vibrates in only one direction/plane;

rotate the metal grid/detector;

until minimum signal is detected;

or

electric field vector vibrates in only one direction/plane;

rotate transmitter through an angle;

need to rotate receiver through same angle to restore signal in transmitter;

Few were able to give complete and convincing explanations of the formation of the standing wave. Common errors were to omit the consequence of the reflection at the metal plate. Superposition was often poorly or even not described. Details of the phase relationships were also poor.

(i) and (ii) Candidates were very comfortable with these calculations although the number of wavelengths in (i) was often incorrect. Errors from (i) were carried forward to (ii) allowing many cases of full credit in this second part.

Examiners saw very few good descriptions of the polarization demonstration. A number of techniques are available but it is clear that candidates have either not discussed these or find the concept difficult.