Q. No.A concave lens of focal length \(25~\text{cm}\) produces an image \(\frac{1}{10}\text{th}\) of the size of the object. The distance of the object from the lens is:
| 1. | \(225~\text{cm}\) | 2. | \(250~\text{cm}\) |
| 3. | \(150~\text{cm}\) | 4. | \(175~\text{cm}\) |
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| 1. | the effective focal length is \(15~\text{cm}.\) |
| 2. | the chromatic aberration is minimized. |
| 3. | the combination behaves like a convergent lens. |
| 4. | all of these. |
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| 1. | \(60~\text{cm}\) | 2. | \(120~\text{cm}\) |
| 3. | \(30~\text{cm}\) | 4. | \(180~\text{cm}\) |
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Choose the correct statement from the following:
| 1. | \(f' = f,f'' =2f\) | 2. | \(f' = 2f, f''=f\) |
| 3. | \(f' =f, f''=f\) | 4. | \(f'=2f, f''=2f\) |
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A lens forms an image of a point object placed at distance \(20~\text{cm}\) from it. The image is formed just in front of the object at a distance \(4~\text{cm}\) from the object (and towards the lens). The power of the lens is:
1. \(-2.25~\text D\)
2. \(1.75~\text D\)
3. \(-1.25~\text D\)
4. \(1.4~\text D\)
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In the diagram shown below, the image of the point object \(O\) is formed at \(l\) by the convex lens of focal length \(20~\text{cm},\) where \(F_1\) and \(F_2\) are foci of the lens. The value of \(x'\) is:
| 1. | \(10~\text{cm}\) | 2. | \(20~\text{cm}\) |
| 3. | \(30~\text{cm}\) | 4. | \(40~\text{cm}\) |
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A thin equiconvex lens of power \(P\) is cut into three parts \(A,B,\) and \(C\) as shown in the figure. If \(P_1,P_2\) and \(P_3\) are powers of the three parts respectively, then:
| 1. | \(P_1=P_2=P_3\) | 2. | \(P_1>P_2=P_3\) |
| 3. | \(P_1<P_2=P_3\) | 4. | \(P_2=P_3=2P_1\) |
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Two similar plano-convex lenses are combined together in three different ways as shown in the adjoining figure. The ratio of the focal lengths in three cases will be:
1. \(2:2:1\)
2. \(1:1:1\)
3. \(1:2:2\)
4. \(2:1:1\)
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| 1. | \(X+Y\) | 2. | \(\dfrac{X +Y}{2}\) |
| 3. | \(X-Y\) | 4. | \(\dfrac{X -Y}{2}\) |
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If the space between two convex lenses of glass in the combination shown in the figure below is filled with water, then:
| 1. | the focal length of the system will decrease. |
| 2. | the focal length of the system will increase. |
| 3. | the power of the system will increase. |
| 4. | the power of the system will become infinite. |
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