If we observe the single slit Fraunhofer diffraction with a wavelength $\lambda$ and slit width d, the width of the central maximum is 2$\theta$. On decreasing the slit width for the same $\lambda$

1.  $\theta$ increases

2.  $\theta$ remains unchanged

3.  $\theta$ decreases

4.  $\theta$ increases or decreases depending on the intensity of light

A slit of width a is illuminated by white light. For red light $\left(\mathrm{\lambda } = 6500 \stackrel{0}{A}\right)$, the first minima is obtained at $\theta$ = $30°$. Then the value of a will be:

1.  3250 $\stackrel{0}{A}$

2.  $6.5 \times {10}^{-14}$ mm

3.  1.24 microns

4.  $2.6 \times {10}^{-4}$ cm

In the case of linearly polarized light, the magnitude of the electric field vector:

1.  does not change with time

2.  varies periodically with time

3.  increases and decreases linearly with time

4.  is parallel to the direction of propagation

Laser light is considered to be coherent because it consists of:

1.  many wavelength

2.  uncoordinated wavelength

3.  coordinated waves of exactly the same wavelength

4.  divergent beam

Two waves originating from the source $S_1 \mathrm{and} S_2$ having zero phase difference and common wavelength $\lambda$ will show completely destructive interference at a point P if $\left(S_1 P - S_2 P\right)$ is

1.  5$\lambda$

2.  3$\lambda$/4

3.  2$\lambda$

4.  11$\lambda$/2

A ray of light of intensity I is incident on a parallel glass-slab at point A as shown in the figure. It undergoes partial reflection and refraction. At each reflection, 25% of incident energy is reflected. The rays AB and A'B' undergo interference. The ratio $I_{max}/I_{min}$ is

1.  4:1

2.  8:1

3.  7:1

4.  49:1

The Young's experiment is performed with the lights of blue $(\lambda =4360 \stackrel{0}{A})$ and green colour $(\lambda =5460 \stackrel{0}{A})$. If the distance of the 4th fringe from the centre is x, then:

1. x (Blue)=x (Green)

2. x(Blue)>x(Green)

3. x(Blue)<x(Green)

4. $\frac{x\left(Blue\right)}{x\left(Green\right)}=\frac{5460}{4360}$

In a Young's double-slit experimental arrangement shown here, if a mica sheet of thickness t and refractive index $\mu$ is placed in front of the slit $S_1$, then the path difference $(S_{1}P-S_{2}P)$:

1. Decreases by $(\mu -1)$t

2. Increases by $(\mu -1)$t

3. Does not change

4. Increases by $\mu$t

In Young's double-slit experiment, if there is no initial phase difference between the light from the two slits, a point on the screen corresponding to the fifth minimum has path difference :

1. $5\frac{\lambda }{2}$

2. $10\frac{\lambda }{2}$

3. $9\frac{\lambda }{2}$

4. $11\frac{\lambda }{2}$

The angular width of the central maximum in the Fraunhofer diffraction for $\lambda =6000 \stackrel{o}{A} is {\theta }_0$. When the same slit is illuminated by another monochromatic light, the angular width decreases by 30%. The wavelength of this light is:

1. $1800 \stackrel{o}{A}$

2. $4200 \stackrel{o}{A}$

3. $420 \stackrel{o}{A}$

4. $6000 \stackrel{o}{A}$