The magnifying power of a telescope is \(9\). When it is adjusted for parallel rays the distance between the objective and eyepiece is \(20~\text{cm}\). The focal length of the lenses is:
1. \(10~\text{cm}, ~10~\text{cm}\)
2. \(15~\text{cm}, ~5~\text{cm}\)
3. \(18~\text{cm}, ~2~\text{cm}\)
4. \(11~\text{cm}, ~9~\text{cm}\)
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 |
1. | Difference between apparent and real depth of the pond |
2. | Mirage on hot summer days |
3. | Brilliance of the diamond |
4. | Working of optical fibre |
A ray of light travelling in a transparent medium of refractive index \(\mu\) falls on a surface separating the medium from the air at an angle of incidence of \(45^{\circ}\). For which of the following value of \(\mu\), the ray can undergo total internal reflection?
1. \(\mu = 1.33\)
2. \(\mu =1.40\)
3. \(\mu=1.50\)
4. \(\mu = 1.25\)
A lens having focal length \(f\) and aperture of diameter d forms an image of intensity \(I\). An aperture of diameter \(\frac{d}{2}\)in central region of lens is covered by a black paper. The focal length of lens and intensity of the image now will be respectively:
1. \(f\) and \(\frac{I}{4}\)
2. \(\frac{3f}{4}\) and \(\frac{I}{2}\)
3. \(f\) and \(\frac{3I}{4}\)
4. \(\frac{f}{2}\) and \(\frac{I}{2}\)
Two thin lenses of focal lengths f1 and f2 are in contact and coaxial. The power of the combination is:
1.
2.
3.
4. None of the above
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 |
A small coin is resting on the bottom of a beaker filled with a liquid. A ray of light from the coin travels up, to the surface of the liquid and moves along its surface (see figure).
How fast is the light traveling in the liquid?
1. | \(1.8 \times 10^8 \mathrm{~m} / \mathrm{s} \) | 2. | \(2.4 \times 10^8 \mathrm{~m} / \mathrm{s} \) |
3. | \(3.0 \times 10^8 \mathrm{~m} / \mathrm{s} \) | 4. | \(1.2 \times 10^8 \mathrm{~m} / \mathrm{s}\) |
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
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