A security camera on the ship captures an image of two green lamps on the shore. The lamps emit light of wavelength 520 nm.

The camera has a circular aperture of diameter 6.2 mm. The lamps are separated by 1.5 m. Determine the maximum distance between the camera and the lamps at which the images of the lamps can be distinguished.

Describe the polarization of the sunlight that is reflected from the sea.

Outline how polarized sunglasses help to reduce glare from the sea.

use of \(\theta  = \frac{{1.22\lambda }}{d}\);

\(\left( {\frac{{1.22 \times 520 \times {{10}^{ - 9}}}}{{6.2 \times {{10}^{ - 3}}}}} \right) = 1.02 \times {10^{ - 4}}\);

distance \( = \left( {\frac{{1.5}}{{1.02 \times {{10}^{ - 4}}}} = } \right)1.47 \times {10^4}{\text{ m}}\);

Award [2 max] if distance is \(1.79 \times {10^4}{\text{ }}m\) (ignoring factor of 1.22) in second marking point.

partially/partly;

plane/horizontally polarized;

the light from the sea is (predominantly) horizontally polarized;

the sunglasses are arranged to admit a particular/vertical plane of polarization;

hence polarized sunglasses absorb much of the reflected light/glare;

The Rayleigh criterion for a circular aperture was almost always used to find resolving power correctly. The third mark for finding distance was often lost as some candidates used tanθ (with their calculator in degree mode) or used 750m instead of 1500m in their calculation.

Two marks were obtained for stating that the reflected light from the sea was partially plane/horizontally polarised. Most candidates obtained only one mark. Many obtained no mark as they simply stated that the light would be polarised – which is essentially rewording the question.

This was a 3 mark question, so candidates needed to give a detailed response, including the respective planes of polarisation of reflected light and the polaroid, in explaining the action of polarising sunglasses.