Q. No.An object is placed at a distance of \(40\) cm from a concave mirror of a focal length of \(15\) cm. If the object is displaced through a distance of \(20\) cm towards the mirror, the displacement of the image will be:
1.
\(30\) cm away from the mirror
2.
\(36\) cm away from the mirror
3.
\(30\) cm towards the mirror
4.
\(36\) cm towards the mirror
A person can see objects clearly only when they lie between \(50\) cm and \(400\) cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be:
| 1. | convex, \(+2.25\) D | 2. | concave, \(-0.25\) D |
| 3. | concave, \(-0.2\) D | 4. | convex, \(+0.5\) D |
An astronomical refracting telescope will have large angular magnification and high angular resolution when it has an objective lens of:
| 1. | small focal length and large diameter. |
| 2. | large focal length and small diameter. |
| 3. | large focal length and large diameter. |
| 4. | small focal length and small diameter. |
An astronomical telescope has an objective and eyepiece of focal lengths \(40\) cm and \(4\) cm respectively. To view an object \(200\) cm away from the objective, the lenses must be separated by a distance:
| 1. | \(46.0\) cm | 2. | \(50.0\) cm |
| 3. | \(54.0\) cm | 4. | \(37.3\) cm |
In an astronomical telescope in normal adjustment, a straight line of length \(L\) is drawn on the inside part of the objective lens. The eye-piece forms a real image of this line. The length of this image is \(l.\) The magnification of the telescope is:
1. \(\frac{L}{l}+1\)
2. \(\frac{L}{l}-1\)
3. \(\frac{L+1}{l-1}\)
4. \(\frac{L}{l}\)
| 1. | virtual, upright, height \(=0.5\) cm |
| 2. | real, inverted, height \(=4\) cm |
| 3. | real, inverted, height \(=1\) cm |
| 4. | virtual, upright, height \(=1\) cm |
A double convex lens has a focal length of \(25\) cm. The radius of curvature of one of the surfaces is double of the other. What would be the radii if the refractive index of the material of the lens is \(1.5?\)
| 1. | \(100\) cm, \(50\) cm |
| 2. | \(25\) cm, \(50\) cm |
| 3. | \(18.75\) cm, \(37.5\) cm |
| 4. | \(50\) cm, \(100\) cm |
A ray is incident at an angle of incidence \(i\) on one surface of a small angle prism (with angle of prism \(A\)) and emerges normally from the opposite surface. If the refractive index of the material of the prism is \(\mu,\) then the angle of incidence is nearly equal to:
| 1. | \(\frac{2A}{\mu}\) | 2. | \(\mu A\) |
| 3. | \(\frac{\mu A}{2}\) | 4. | \(\frac{A}{2\mu}\) |
If the critical angle for total internal reflection from a medium to vacuum is \(45^{\circ}\), the velocity of light in the medium is:
| 1. | \(1.5\times10^{8}~\text{m/s}\) | 2. | \(\frac{3}{\sqrt{2}}\times10^{8}~\text{m/s}\) |
| 3. | \(\sqrt{2}\times10^{8}~\text{m/s}\) | 4. | \(3\times10^{8}~\text{m/s}\) |
A rod of length \(10~\text{cm}\) lies along the principal axis of a concave mirror of focal length \(10~\text{cm}\) in such a way that its end closer to the pole is \(20~\text{cm}\) away from the mirror. The length of the image is:
1. \(15~\text{cm}\)
2. \(2.5~\text{cm}\)
3. \(5~\text{cm}\)
4. \(10~\text{cm}\)
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