A slit S is illuminated by a monochromatic suorce of light to give two coherent sources P_{1} and P_{2} . These give a dark band at the point R on the screen as shown in figure.

1. Write the formula to find out bandwidth.

2. What relationship must exist between the length P_{1} R and P_{2} R?

3. Can interference fringes be produced by using two identical bulbs?

4. If the distance between P_{1} and P_{2} is 1 mm and the screen is placed in 1m away, what is the fringe separation for a light of wavelength 5 × 10^{-7} m?