State one assumption made in deriving the formula n 2 v − n 1 u = n 2 − n 1 R for refraction at a spherical interface.

While deriving the formula for refraction at a spherical interface, the assumption made is that the aperture of the spherical surface is small. In such a case the point of incidence will be close to the pole of the spherical surface due to which the angle of incidence and angle of refraction will be small too. Hence, in radian, sin i = i and sin r = r which is one of the important steps in the derivation of the formula n 2 v − n 1 u = n 2 − n 1 R .

State one assumption made in deriving the formula n 2 v − n 1 u = n 2 − n 1 R for refraction at a spherical interface.

While deriving the formula for refraction at a spherical interface, the assumption made is that the aperture of the spherical surface is small. In such a case the point of incidence will be close to the pole of the spherical surface due to which the angle of incidence and angle of refraction will be small too. Hence, in radian, sin i = i and sin r = r which is one of the important steps in the derivation of the formula n 2 v − n 1 u = n 2 − n 1 R .

E M B I B E

ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 1

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IMPORTANT

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State one assumption made in deriving the formula $\frac{n_{2}}{v} - \frac{n_{1}}{u} = \frac{n_{2} - n_{1}}{R}$ for refraction at a spherical interface.

Important Questions on Refraction of Light at Spherical Surfaces : Lenses

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IMPORTANT

ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 2

Can the optical centre of a lens be situated outside the lens?

HARD

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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 3

A thin convex lens $(L_{1})$ of focal length $80 cm$ and a thin concave lens $(L_{2})$ of focal length $f$ are kept co-axially $20 cm$ apart as shown in figure below. When a narrow and parallel beam of light is incident on the convex lens, beam emerging from the concave lens is also a parallel beam. Find $f$ .

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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 4

Write down the lens maker’s formula, using standard symbols.

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IMPORTANT

ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 5

How does focal length of a convex lens change with increase in wavelength of incident light?

MEDIUM

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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 6

Under what condition is the first focal length of a lens not equal to its second focal length?

EASY

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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 7

The image of an object, placed at a distance of $25 cm$ from a lens, is formed at a distance of $40 cm$ on the other side of the lens. If the object is placed at a distance of $40 cm$ from the lens, find the position of the image.

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ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 8

A convex lens forms a virtual image of an object. Where is the object? Answer in terms of focal length.

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IMPORTANT

ISC Physics Class 12, Part-2>Chapter 3 - Refraction of Light at Spherical Surfaces : Lenses>QUESTIONS>Q 9

Where should an object be placed in order to form an image of the same size by a convex lens? Can it happen in case of a concave lens also?