Q. No.A rainbow is formed due to:
1.
Scattering & refraction
2.
Total internal reflection & dispersion
3.
Reflection only
4.
Diffraction and dispersion
A plane convex lens \((\mu= 1.5)\) has a radius of curvature \(10~\text{cm}\). It is silvered on its plane surface. The focal length of the lens after silvering is:
| 1. | \(10\) cm | 2. | \(20\) cm |
| 3. | \(15\) cm | 4. | \(25\) cm |
Light enters at an angle of incidence in a transparent rod of refractive index \(n.\) For what value of the refractive index of the material of the rod, will the light, once entered into it, not leave it through its lateral face whatsoever be the value of the angle of incidence?
| 1. | \(n>\sqrt{2}\) | 2. | \(1.0\) |
| 3. | \(1.3\) | 4. | \(1.4\) |
A tall man, of height \(6\) feet, wants to see his full image. The required minimum length of the mirror will be:
| 1. | \(12\) feet | 2. | \(3\) feet |
| 3. | \(6\) feet | 4. | Any length |
1. \(3.75\) cm
2. \(3\) cm
3. \(10.5\) cm
4. \(2.5\) cm
| 1. | Two points propagating in two different parallel directions |
| 2. | One point propagating in two different directions through the slab |
| 3. | One point propagating in the same direction through the slab |
| 4. | Two points propagating in two different non-parallel directions |
The refractive index of the material of a prism is and its refracting angle is \(30^{\circ}\). One of the refracting surfaces of the prism is made a mirror inwards. A beam of monochromatic light entering the prism from the other face will retrace its path after reflection from the mirrored surface if its angle of incidence on the prism is:
| 1. | \(60^{\circ}\) | 2. | \(0^{\circ}\) |
| 3. | \(30^{\circ}\) | 4. | \(45^{\circ}\) |
For the given incident ray as shown in the figure, in the condition of the total internal reflection of this ray, the minimum refractive index of the prism will be:
| 1. | \(\dfrac{\sqrt{3} + 1}{2}\) | 2. | \(\dfrac{\sqrt{2} + 1}{2}\) |
| 3. | \(\sqrt{\dfrac{3}{2}}\) | 4. | \(\sqrt{\dfrac{7}{6}}\) |
If refractive index of a prism is \(\mathrm{cot(A/2)}\), then the minimum angle of deviation is:
1. \(180^{\circ}-A\)
2. \(180^{\circ}-2A\)
3. \(90^{\circ}-A\)
4. \((A/2)\)
| 1. | Only \(\frac{d}{4}\) |
| 2. | Only \(\frac{d}{2}\) |
| 3. | More than \(\frac{d}{4}\) but less than \(\frac{d}{2}\) |
| 4. | Less than or equal to \(\frac{d}{4}\) |
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