Q. No.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. \(3:4\)
2. \(2:1\)
3. \(1:2\)
4. \(2:3\)
Assertion: For observing traffic at our back, we prefer to use a convex mirror.
Reason: A convex mirror has a much larger field of view than a plane mirror or a concave mirror.
- If both the assertion and the reason are true and the reason is a correct explanation of the assertion
- If both the assertion and reason are true but the reason is not a correct explanation of the assertion
- If the assertion is true but the reason is false
- If both the assertion and reason are false
| 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
How fast is the light traveling in the liquid?
| 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 |
| 1. | \(180^\circ-3A\) | 2. | \(180^\circ-2A\) |
| 3. | \(90^\circ-A\) | 4. | \(180^\circ+2A\) |
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