A parallel beam of moving electrons is incident normal on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the slit is further narrowed, then which of the following statement is correct?

1.  The 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 remain the same.

In Young's double-slit experiment, the slits are 0.4 mm apart and illuminated by photons of two wavelengths ${\lambda }_1$ = 600 nm and ${\lambda }_2$ = 700nm. At what minimum distance from the common center, bright fringe from one interference pattern coincides with bright fringe from other? (Given that the distance of the screen from the plane of slits is 80cm.)

1.  7.2 mm

2.  6.0 mm

3.  8.4 mm

4.  9.8 mm

A diffraction pattern is observed using a beam of red light. What will happen if the red light is replaced by the blue light?

1.  No change takes place

2.  Diffraction bands become narrower

3.  Diffraction bands become broader

4.  Diffraction pattern disappears

The phenomenon of polarisation justify which nature of light?

1.  longitudinal 

2.  transverse

3.  both

4.  geometrical

Two waves of intensity ratio 9:1 interfere to produce fringes in a young's double-slit experiment, the ratio of  intensity at maxima  to the intensity at minima is

1.  4:1

2.  9:1

3.  81:1

4.  9:4

Interference fringes are produced using white light in a double-slit arrangement. When a mica sheet of uniform thickness of the refractive index 1.6 (relative to air) is placed in the path of light from one of the slits, the central fringe moves by a distance.

This distance is equal to the width of 30 interference bands. If the light of wavelength 4800 $\stackrel{\mathrm{o}}{\mathrm{A}}$ is used, the thickness (in $\mu$m) of mica is —

1.  90

2.  12

3.  14

4.  24

Young's double-slit experiment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5th dark fringe lies in the air. The refractive index of the medium is nearly 

(a)1.25 

(b) 1.59 

(c) 1.69

(d) 1.78 

Two polaroids $P_1 and P_2$ are placed with their axis perpendicular to each other. Unpolarised light $I_o$ is incident on $P_1$. A third polaroid $P_3$ is kept in between $P_1 and P_2$ such that its axis makes an angle ${45}^{°}$ with that of $P_1$. The intensity of transmitted light through $P_2$

(a)$\frac{I_o}{2}$

(b) $\frac{I_o}{4}$

(c) $\frac{I_o}{8}$

(d) $\frac{I_o}{16}$

The interference pattern is obtained with two coherent light sources of intensity ratio n. In the interference pattern, the ratio $\frac{I_{max}-I_{min}}{I_{max}+I_{min}}$ will be

1.$\frac{\sqrt{n}}{n+1}$             

2. $\frac{2\sqrt{n}}{n+1}$

3. $\frac{\sqrt{n}}{{\left(n+1\right)}^2}$         

4.$\frac{2\sqrt{n}}{{\left(n+1\right)}^2}$

A linear aperture whose width is 0.02 cm is placed immediately in front of a lens of focal length 60 cm. The aperture is illuminated normally by a parallel beam of wavelength $5\times {10}^{-5}$ cm. The distance of the first dark band of the diffraction pattern from the centre of the screen is

(a) 0.10 cm             (b) 0.25 cm 

(c) 0.20 cm             (d) 0.15 cm