Physics 9702 · AS & A Level · Interference

Interference — practice question

Two sources X and Y emit microwaves in phase, with the same wavelength and amplitude, as illustrated in Fig. 5.1. A microwave detector is then moved along a route parallel to the line joining X and Y. An interference pattern is observed. A central intensity maximum is found at point A, and a neighbouring intensity minimum is at point B. The microwaves have a wavelength of $0.040\text{ m}$.
(a)[3]

Calculate the frequency of the microwaves, in GHz.

(b(i))[1]

Determine the path difference for the waves reaching point B.

(b(ii))[1]

Determine the phase difference for the waves reaching point B.

(c)[2]

The amplitudes from the sources are altered. This changes the amplitude of the waves arriving at point A. At this point, the amplitude of the wave from source X is doubled and the amplitude of the wave from source Y is also doubled. Describe the effect, if any, on the intensity of the central maximum at point A.

(d(i))[1]

Describe the effect, if any, on the positions of the central intensity maximum and the adjacent intensity minimum when the separation between the sources X and Y is increased.

(d(ii))[1]

Describe the effect, if any, on the positions of the central intensity maximum and the adjacent intensity minimum when the phase difference between the microwaves emitted by the sources X and Y changes to $180^\circ$.

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