A light ray from the air is incident (as shown in the figure) at one end of glass fibre (refractive index \(\mu= 1.5\)) making an incidence angle of \(60^{\circ}\) on the lateral surface so that it undergoes a total internal reflection. How much time would it take to traverse the straight fibre of a length of \(1\) km?
1. \(3.33~\mu\text{s}\)
2. \(6.67~\mu\text{s}\)
3. \(5.77~\mu\text{s}\)
4. \(3.85~\mu\text{s}\)
Choose the correct mirror image of the figure:
1. | 2. | ||
3. | 4. |
1. | \(8\) | 2. | \(10\) |
3. | \(12\) | 4. | \(16\) |
If the focal length of the objective lens is increased, then magnifying power of:
1. | microscope will increase but that of telescope decrease |
2. | microscope and telescope both will increase |
3. | microscope and telescope both will decrease |
4. | microscope will decrease but that of the telescope will increase |
1. | \(\mu A \) | 2. | \(\frac{\mu A}{2} \) |
3. | \(A / \mu \) | 4. | \(A / 2 \mu\) |
A concave mirror of the focal length \(f_1\) is placed at a distance of \(d\) from a convex lens of focal length \(f_2\). A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity. The distance \(d\) must be equal to:
1. \(f_1 +f_2\)
2. \(-f_1 +f_2\)
3. \(2f_1 +f_2\)
3. \(-2f_1 +f_2\)
The magnifying power of a telescope is \(9\). When it is adjusted for parallel rays the distance between the objective and eyepiece is \(20\) cm. The focal lengths of lenses are:
1. | \(10~\text{cm}, 10~\text{cm}\) | 2. | \(15~\text{cm}, 5~\text{cm}\) |
3. | \(18~\text{cm}, 2~\text{cm}\) | 4. | \(11~\text{cm}, 9~\text{cm}\) |
In an astronomical telescope, the focal length of the objective lens is \(100\) cm and of the eyepiece is \(2\) cm. The magnifying power of the telescope for the normal eye is:
1. | \(50\) | 2. | \(10\) |
3. | \(100\) | 4. | \(\dfrac{1}{50}\) |
1. | \(\dfrac{\pi}{4}\) | 2. | \(\sin^{- 1} \left(\frac{3}{4}\right)\) |
3. | \(\frac{1}{2} \sin^{- 1} \left(\frac{3}{4}\right)\) | 4. | \(2\sin^{- 1} \left(\frac{3}{4}\right)\) |
1. | \(10\) cm | 2. | \(15\) cm |
3. | \(20\) cm | 4. | \(30\) cm |