In Young’s double slit experiment. the slits are 2 mm apart and are illuminated by photons of two wavelengths , λ₁= 12000Å and , λ₂= 10000Å. At what minimum distance from the common central bright fringe on the screen 2m from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other?

(a) 8mm

(b) 6mm

(c) 4 mm

(d) 3mm

A parallel beam of fast-moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, then which of the following statements is correct?

(1) Diffraction pattern is not observed on the screen in the case of electrons

(2) The angular width of the central maximum of the diffraction pattern will increase

(3) The angular width of the central maximum will decrease

(4) The angular width of the central maximum will be unaffected

In a double slit experiment, the distance between the slits is 3 mm and the slits are 2 m away from the screen one due to light with wavelength 480 nm, and the other due to light with wavelength 600 nm. What is the separation on the screen between the fifth order bright fringes of the two interference patterns ?

1. $4\times {10}^{-4}$

2. $9\times {10}^{-4}$

3. $3\times {10}^{-4}$

4. $5\times {10}^{-4}$

Two coherent sources of light can be obtained by:

(1) Two different lamps

(2) Two different lamps but of the same power

(3) Two different lamps of the same power and have the same colour

(4) None of the above

By Huygen's wave theory of light, we cannot explain the phenomenon of:

Two coherent monochromatic light beams of intensities I and 4I are superposed. The maximum and minimum possible intensities in the resulting beam are 

(1) 5I and I

(2) 5I and 3I

(3) 9I and I

(4) 9I and 3I

If L is the coherence length and c the velocity of light, the coherent time is 

(1) cL

(2) $\frac{L}{c}$

(3) $\frac{c}{L}$

(4) $\frac{1}{Lc}$

If the amplitude ratio of two sources producing interference is 3 : 5, the ratio of intensities at maxima and minima is 

(1) 25 : 16

(2) 5 : 3

(3) 16 : 1

(4) 25 : 9

For constructive interference to take place between two monochromatic light waves of wavelength λ, the path difference should be 

(1) $(2n-1)\frac{\lambda }{4}$

(2) $(2n-1)\frac{\lambda }{2}$

(3) $n\lambda$

(d) $(2n+1)\frac{\lambda }{2}$

Soap bubble appears coloured due to the phenomenon of:
1. Interference
2. Diffraction
3. Dispersion
4. Reflection