Two coherent sources are apart

PHYSICS · Subjective · A Level · Physics · Waves · Waves

Problem

Two coherent sources are

0.3\text{ mm}

apart. They are

0.9\text{ m}

away from the screen. The second dark fringe is at a distance of

0.3\text{ cm}

from the centre. Find the distance of the fourth bright fringe from the centre. Also, find the wavelength of light used.