A biconvex lens has power \(P.\) It is cut into two symmetrical halves by a plane containing the principal axis. The power of one part will be:
1. | \(0\) | 2. | \(\dfrac{P}{2}\) |
3. | \(\dfrac{P}{4}\) | 4. | \(P\) |
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
Two similar thin equi-convex lenses, of focal length \(f\) each, are kept coaxially in contact with each other such that the focal length of the combination is \(F_1\). When the space between the two lenses is filled with glycerin which has the same refractive index as that of glass \((\mu = 1.5),\) then the equivalent focal length is \(F_2\). The ratio \(F_1:F_2\) will be:
1. \(3:4\)
2. \(2:1\)
3. \(1:2\)
4. \(2:3\)
1. | \(90^{\circ}\) |
2. | \(180^{\circ}\) |
3. | \(0^{\circ}\) |
4. | equal to the angle of incidence |
Pick the wrong statement in the context with a rainbow.
1. | Rainbow is a combined effect of dispersion, refraction, and reflection of sunlight. |
2. | When the light rays undergo two internal reflections in a water drop, a secondary rainbow is formed. |
3. | The order of colors is reversed in the secondary rainbow. |
4. | An observer can see a rainbow when his front is towards the sun. |
A convex lens and a concave lens, each having the same focal length of 25 cm, are put in contact to form a combination of lenses. The power in dioptres of the combination is:
1. 25
2. 50
3. infinite
4. zero
A microscope is focused on a mark on a piece of paper and then a slab of glass of thickness 3 cm and a refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?
1. 1 cm upward
2. 4.5 cm downward
3. 1 cm downward
4. 2 cm upward
The frequency of a light wave in a material is 2×1014 Hz and the wavelength is 5000 Å. The refractive index of the material will be:
1. 1.40
2. 1.50
3. 3.00
4. 1.33
1. | \(1.8 \times 10^8 ~\text{m/s}\) | 2. | \(2.4 \times 10^8~\text{m/s}\) |
3. | \(3.0 \times 10^8~\text{m/s}\) | 4. | \(1.2 \times 10^8~\text{m/s}\) |
A boy is trying to start a fire by focusing sunlight on a piece of paper using an equiconvex lens of a focal length of \(10\) cm. The diameter of the sun is \(1.39\times10^9\) m and its mean distance from the earth is \(1.5\times10^{11}\) m. What is the diameter of the sun's image on the paper?
1. | \(9.2\times10^{-4}\) m | 2. | \(6.5\times10^{-4}\) m |
3. | \(6.5\times10^{-5}\) m | 4. | \(12.4\times10^{-4}\) m |