Rays of light from two coherent sources produces constructive interference. Which of the following cannot be the phase difference between these two rays?

(A) $0°$

(B) $270°$

(C) $360°$

(D) $720°$

(a) Copy the waves shown in the diagram onto a sheet of graph paper and use the principle of superposition to sketch the resultant wave.

(b) Compare the wavelength of the resultant wave with that of the component waves.

State how the diffracted pattern will change when:

(a) The wavelength of the incident wave is increased

State how the diffracted pattern will change when:

(b) The wavelength of the incident wave is decreased.

A constant frequency signal from a signal generator is fed to two loudspeakers placed $1.5 \mathrm{m}$ apart. A student, who is $8.0 \mathrm{m}$ away from the loudspeakers, walks across in a line parallel to the line between the loudspeakers. The student measures the distance between successive spots of loudness to be $1.2 \mathrm{m}$. Calculate:

(a) The wavelength of the sound

A constant frequency signal from a signal generator is fed to two loudspeakers placed $1.5 \mathrm{m}$ apart. A student, who is $8.0 \mathrm{m}$ away from the loudspeakers, walks across in a line parallel to the line between the loudspeakers. The student measures the distance between successive spots of loudness to be $1.2 \mathrm{m}$. Calculate:

(b) The frequency of the sound (assume the speed of sound is $330 \mathrm{m}{ \mathrm{s}}^{-1}$)