physics - light

1. (a) Diffraction
(b) Interference

(c) Alternate maximum and minimum readings are recorded by the milliammeter. The max reading corresponds to location of constructive interference, whereas the min reading corresponds to position of destructive interference.

(d) At Q, the path difference between waves from S1 and S2 = one wavelength
hence, path difference = 3 cm

2. (a)(i) Position A is the central max. Path difference = 0 m
(ii) Position B is the 1st dark band, path difference = wavelength/2 = 600/2 nm = 300 nm
(iii) Position C is the 2nd bright band, path difference = 2 x wavelength = 2x600 nm = 1200 nm

(b) The separation between the bright bands decreases.

3. (a) The diagram has not been given here.

(b) The cooling of the exhausts lowers the temperature of the gas, thus reduce the amount of infrared emitted. This could prevent the detection by infrared sensor.

(c) The aircraft is designed to blend in with the background to reduce visual detection.
The engines of the aircraft are quiet.

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