Extra Questions for Class 12 Physics Chapter 9 Ray Optics and Optical Instrument

Here we are providing extra questions for class 12 physics. In this article we have covered class 12 physics chapter 9 Ray optics and Optical Instrument. Different kind of questions are included to give students an idea about every possible question related to the chapter.

Extra Questions for Class 12 Physics Chapter 9 Ray Optics and Optical Instrument

Very Short Answer Questions

Q.1. How does the angle of minimum deviation of a glass prism vary if the incident violet light is
replaced by red light?

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Answer: The angle of minimum deviation decreases, if violet light is replaced by red light.

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Q.2. For the same angle of incidence, the angle of refraction in two media A and B are 25° and 35° respectively. In which one of the two media is the speed of light lesser?

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Answer:

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Q.3. Why does bluish colour predominate in a clear sky?

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Answer: The colour of the sky, as seen from the earth, is due to the scattering of sunlight by molecules of earth’s atmosphere. The amount of scattering is inversely proportional to the fourth power of the wavelength.
Thus, shorter wavelengths are scattered much more than longer wavelengths.
Since λ_B<< λ_R. Hence, the bluish colour predominates in the clear sky.

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Q.4. A ray of light falls on a transparent sphere with centre ‘C’ as shown in the figure. The ray
emerges from the sphere parallel to the line AB. Find the angle of refraction at A if refractive
index of the material of the sphere is √3.

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Answer:

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Q.5. When light travels from an optically denser medium to a rarer medium, why does the critical angle of incidence depend on the colour of light?

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Answer: The refractive index is different for different colour wavelength. Hence, critical angle would also be different for different colour of light.

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Fill in the blanks:

(i) A lens of power of –4.0 D means a concave lens of focal length _____ cm.

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Answer: –25 cm

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(ii) For the same angle of incidence, the angles of refraction in three different medium A, B and C are 15°, 25° and 35° respectively. In medium _____ velocity of light will be minimum.

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Answer: A

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(iii) When the refractive index of the material of the lens is greater than that of the surroundings, then biconvex lens acts as a _____.

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Answer: converging lens

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(iv) The power of a lens is defined as the _____ of the angle by which it converges or diverges a beam of light falling at unit distant from the optical centre.

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Answer: tangent

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(v) When we apply the sign convention, we see that, for erect and virtual image formed by a convex or concave lens, m is _____.

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Answer: positive

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(vi) The largest telescope in India is in Kavalur, Tamil Nadu. It is a _____ diameter reflecting telescope (Cassegrain).

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Answer: 2.34 m

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(vii) The angle between the emergent ray and the direction of the incident ray is called the _____.

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Answer: angle of deviation

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(viii) In the visible spectrum, red light is at the long wavelength end (~700 nm) while the _____ is at the short wavelength end (~400 nm).

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Answer: violet light

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(ix) At the minimum deviation, the refraction ray inside the prism becomes parallel to the _____.

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Answer: base

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(x) The amount of scattering is inversely proportional to the _____ power of the wavelength.

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Answer: fourth

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