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. |
A beam of light consisting of red, green, and blue colours is incident on a right-angled prism. The refractive index of the material of the prism for the red, green, and blue wavelengths is \(1.39\), \(1.44\), and \(1.47\) respectively.
The prism will:
1. | separate the blue colour part from the red and green colour |
2. | separate all the three colours from one another |
3. | not separate the three colours at all |
4. | separate the red colour part from the green and blue colours |
Two identical thin plano-convex glass lenses (refractive index = \(1.5\)) each having radius of curvature of \(20\) cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of a refractive index of \(1.7\). The focal length of the combination is:
1. \(-20\) cm
2. \(-25\) cm
3. \(-50\) cm
4. \(50\) cm
1. | \(180^\circ-3A\) | 2. | \(180^\circ-2A\) |
3. | \(90^\circ-A\) | 4. | \(180^\circ+2A\) |
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
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
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. |