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Q. No.A thin equi-convex lens of refractive index \(1.2\) is dipped in oil of index \(1.44.\) The lens has a power of \(2\) D (in air). When it is immersed in the oil, the focal length of the lens becomes:
1. \(50\) cm
2. \(-50\) cm
3. \(-50/1.2\) cm
4. \(-50 \times1.2\) cm
Subtopic: Lens Makers' Formula |
55%
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The following diagram shows light travelling from \(A\) to \(B\) after bouncing off a plane mirror at \(P\). The time taken is \(t_{APB}\). If, however, light were to take a different path, \(AQB\) (shown by the dotted line), the time taken is \(t_{AQB}\).
Then,
Then,
| 1. | \(t_{APB}=t_{AQB}\) |
| 2. | \(t_{APB}<t_{AQB}\) |
| 3. | \(t_{APB}>t_{AQB}\) |
| 4. | \(t_{APB}\) maybe greater than or less than \(t_{AQB}\) depending on whether \(Q\) is to the left or right of \(P\). |
Subtopic: Reflection at Plane Surface |
From NCERT
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Given below are two statements:
| Assertion (A): | Parallel rays of light of different colours fail to converge to a point after reflection from a spherical mirror. |
| Reason (R): | The refractive index of any material depends on the frequency of light. |
| 1. | (A) is True but (R) is False. |
| 2. | (A) is False but (R) is True. |
| 3. | Both (A) and (R) are True and (R) is a correct explanation of (A). |
| 4. | Both (A) and (R) are True but (R) is not a correct explanation of (A). |
Subtopic: Reflection at Spherical Surface |
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A small object is placed on the principal axis of a convex lens and it forms a real image with a (transverse) magnification of \(2.\) If the object were to move perpendicular to the principal axis with a speed \(u,\) the speed of the image will be:
| 1. | \(u\) | 2. | \(u/2\) |
| 3. | \(2u\) | 4. | \(4u\) |
Subtopic: Reflection at Spherical Surface |
From NCERT
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An equi-convex lens of focal length \(20\) cm (in the air) is split into two parts by a surface that has half the curvature of either of its outer surfaces. The ratio of the powers of the two lenses thus formed is:
1. \(3:1\)
2. \(2:1\)
3. \(1:1\)
4. \(-2:1\)
1. \(3:1\)
2. \(2:1\)
3. \(1:1\)
4. \(-2:1\)
Subtopic: Lenses |
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An equi-convex lens of focal length \(50~\text{cm}\) and an equi-concave lens of the same focal length are placed \(50~\text{cm}\) apart, with a common principal axis. A point object is placed on the principal axis of the system, at a distance of \(100~\text{cm}\) in front of the convex lens (see figure). The final image is formed at:
| 1. | \(100~\text{cm}\) in front of the concave lens |
| 2. | \(50~\text{cm}\) in front of the concave lens |
| 3. | \(50~\text{cm}\) behind the concave lens |
| 4. | infinity |
Subtopic: Lenses |
58%
From NCERT
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A plano-convex lens made of glass \((\mu=1.5)\) is placed with its convex surface in a liquid, and it is found that the focal length is doubled. The refractive index of the liquid is:
1. \(3\)
2. \(2\)
3. \(1.25\)
4. \(1.2\)
1. \(3\)
2. \(2\)
3. \(1.25\)
4. \(1.2\)
Subtopic: Lenses |
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A thin prism of refractive index \(\mu = 1.5\) introduces a deviation of \(+1^\circ\) into the path of an incident beam. When this prism is immersed in a liquid of refractive index \(\mu = 2\), the deviation introduced will be:
| 1. | \( \left ( \dfrac{7}{6} \right )^\circ\) | 2. | \( \left ( \dfrac{3}{2} \right )^\circ\) |
| 3. | \(- \left ( \dfrac{1}{2} \right )^\circ\) | 4. | \( \left ( \dfrac{1}{2} \right )^\circ\) |
Subtopic: Prisms |
60%
From NCERT
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Calculate the dispersive power of a thin prism from the following data:
1. \(0.04\)
2. \(0.02\)
3. \(25\)
4. \(50\)
| Colour | Deviation | ||
| Violet | \(2.04^\circ\) | ||
| Yellow | \(2.00^\circ\) | ||
| Red | \(1.96^\circ\) |
2. \(0.02\)
3. \(25\)
4. \(50\)
Subtopic: Prisms |
76%
From NCERT
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A parallel beam of light is incident onto a convex lens and after passing through the lens, it gets reflected from a plane mirror and passes through the lens again. The focal length of the lens is \(f.\) Where should the mirror be placed so that the final beam emerges parallel?
| 1. | Just behind the lens. |
| 2. | At the focus of the lens. |
| 3. | At a distance of \(2f\) from the lens. |
| 4. | At a distance of \(3f\) from the lens. |
Subtopic: Lenses |
68%
From NCERT
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