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Some examples from this set of practice questions
1.
What is meant by the power of a lens? Give its SI unit. When two or more lenses are placed in conta ?
Answer: Ans Power of a lens is the ability of the lens to converge or diverge a ray of light incident on it. It is the reciprocal of the focal length of the lens, i.e. P=1\\f. The SI unit of power is D (dioptre) it f is measured is metre.
2.
State the two laws of reflection of light.
Answer: Ans Laws of reflection of light states that: (i) The angle of incidence is equal to the angle of reflection. (ii) The incident ray, the reflected ray and the normal to the mirror at the point of incidence all lie in the same plane.
3.
The absolute refractive indices of glass and water are 1.5 and 1.33 respectively. In which medium does light travel faster? Calculate the ratio of speeds of light in the two media.
Answer: Ans Refractive index (RI) if glass is 1.5 Refractive index (RI) of water is 1.33 Now, RI of glass with respect to water = RI of glass/RI of water = 1.5/1.33 = 1.127 RI of water with respect to glass = RI of water/RI of glass = 1.33/1.5 = 0.89 Since velocity of light in medium is inversely proportional to its refractive index, the light will travel faster in optically rarer Medium i.e. water.
4.
The image of a candle flame placed at a distance of 30 cm from a mirror is formed on a screen placed in front of the mirror at a distance of 60 cm from it pole. What is the nature of the mirror? Find its focal length. If the height of the flame is 2.4 cm, find the height of its image. State whether the image formed is erect or inverted.
Answer: Ans Here, u = 30, v = -60 As 1/f = 1/u + 1/v = 1/(-60) + 1/(-30) = -1/20 f = 20, The mirror is concave. As the image is formed on the screen, it is real and inverted. From h2/h1 = -v/u = +60/-30 = -2 h2 = -2xh1 = -2 x 2.4 = -4.8 cm This is the size of inverted image.
5.
As the velocity of light increases, the refractive index of the medium decreases. Light enters from air to water having a refractive index of 4/3. Find the speed of light in water. The speed of light in a vacuum is 3*10^{8} m/s.
Answer: Ans The speed of light in water can be calculated using the refractive index of water, which is 4/3. The speed of light in vacuum is 3 × 10^8 m/s. By using the formula n = c/v, where n is the refractive index, c is the speed of light in vacuum, and v is the speed of light in the medium, we can find the speed of light in water. Substitute the values into the formula: 4/3 = (3 × 10^8) / v. By solving for v, the speed of light in water is 2.25 × 10^8 m/s.
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