A slit of width a is illuminated by white light. For red light (λ = 6500 Å), the first minima is obtained at θ = 30°. Then the value of a will be 

(1) 3250 Å

(2) 6.5 × 10^–4 mm

(3) 1.24 microns

(4) 2.6 × 10^–4 cm

The radius of central zone of the circular zone plate is 2.3 mm. The wavelength of incident light is $5893\AA .$ Source is at a distance of 6m. Then the distance of the first image will be 

(1) 9 m

(2) 12 m

(3) 24 m

(4) 36 m

What will be the angular width of central maxima in Fraunhoffer diffraction when light of wavelength \(6000~\mathring{A}\) is used and slit width is \(12\times 10^{-5}\) cm:
1. \(2~\text{rad}\)
2. \(3~\text{rad}\)
3. \(1~\text{rad}\)
4. \(8~\text{rad}\)

The direction of the first secondary maximum in the Fraunhofer diffraction pattern at a single slit is given by:
\((a\) is the width of the slit) 
1. \(a\sin\theta = \frac{\lambda}{2}\)
2. \(a\cos\theta = \frac{3\lambda}{2}\)
3. \(a\sin\theta = \lambda\)
4. \(a\sin\theta = \frac{3\lambda}{2}\)

A parallel monochromatic beam of light is incident normally on a narrow slit. A diffraction pattern is formed on a screen placed perpendicular to the direction of the incident beam. At the first minimum of the diffraction pattern, the phase difference between the rays coming from the edges of the slit is:
1. \(0\)
2. \(\dfrac \pi 2 \)
3. \(\pi\)
4. \(2\pi\)

A parallel beam of monochromatic light of wavelength \(5000~\mathring{A}\) is incident normally on a single narrow slit of width \(0.001\) mm. The light is focused by a convex lens on a screen placed on the focal plane. The first minimum will be formed for the angle of diffraction equal to:
1. \(0^{\circ}\)
2. \(15^{\circ}\)
3. \(30^{\circ}\)
4. \(60^{\circ}\)

In the far field diffraction pattern of a single slit under polychromatic illumination, the first minimum with the wavelength ${\lambda }_1$ is found to be coincident with the third maximum at ${\lambda }_2$. So

(1) $3{\lambda }_1=0.3{\lambda }_2$

(2) $3{\lambda }_1={\lambda }_2$

(3) ${\lambda }_1=3.5{\lambda }_2$

(4) $0.3{\lambda }_1=3{\lambda }_2$

The angle of polarisation for any medium is \(60^\circ,\) what will be the critical angle for this?

A beam of light AO is incident on a glass slab (μ = 1.54) in a direction as shown in figure. The reflected ray OB is passed through a Nicol prism on viewing through a Nicole prism, we find on rotating the prism that, 

1. the intensity is reduced down to zero and remains zero.
2. the intensity reduces down some what and rises again.
3. there is no change in intensity.
4. the intensity gradually reduces to zero and then again increases.

In the propagation of electromagnetic waves, the angle between the direction of propagation and plane of polarisation is:

(1) 0^o

(2) 45^o

(3) 90^o

(4) 180^o