Q. No.A thin convex lens and a thin concave lens are kept in contact and are co-axial. Which of the following statements is correct for this combination of two lenses?
| 1. | behaves as concave lens if \(\left|f_{\text {convex }}\right|>\left|f_{\text {concave }}\right|\) |
| 2. | behaves as concave lens if \(\left|f_{\text {convex }}\right|<\left|f_{\text {concave }}\right|\) |
| 3. | behaves as convex lens if \(\left|f_{\text {convex }}\right|>\left|f_{\text {concave }}\right|\) |
| 4. | Focal length of the lens system will change if the positions of two lenses are interchanged |
Subtopic: Lenses |
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A collimated beam of light of diameter \(2~\text{mm}\) is propagating along \(x\text{-}\)axis. The beam is required to be expanded in a collimated beam of diameter \(14~\text{mm}\) using a system of two convex lenses. If first lens has focal length \(40~\text{mm}\), then the focal length of second lens is: (in mm).
1. \(200\)
2. \(280\)
3. \(300\)
4. \(400\)
1. \(200\)
2. \(280\)
3. \(300\)
4. \(400\)
Subtopic: Lenses |
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A thin convex lens of focal length \(5~\text{cm}\) and a thin concave lens of focal length \(4~\text{cm}\) are combined together (without any gap) and this combination has magnification \(m_1\) when an object is placed \(10~\text{cm}\) before the convex lens. Keeping the positions of the convex lens and object undisturbed, a gap of \(1~\text{cm}\) is introduced between the lenses by moving the concave lens away, which lead to a change in the magnification of the total lens system to \(m_2\) . The value of \(\left|\dfrac{m_1}{m_2}\right|\) is:
1. \(\dfrac{5}{9}\)
2. \(\dfrac{5}{27}\)
3. \(\dfrac{3}{2}\)
4. \(\dfrac{25}{27}\)
1. \(\dfrac{5}{9}\)
2. \(\dfrac{5}{27}\)
3. \(\dfrac{3}{2}\)
4. \(\dfrac{25}{27}\)
Subtopic: Lenses |
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The size of the images of an object, formed by a thin lens are equal when the object is placed at two different positions \(8\) cm and \(24\) cm from the lens. The focal length of the lens is: (in cm)
1. \(10\)
2. \(16\)
3. \(20\)
4. \(30\)
1. \(10\)
2. \(16\)
3. \(20\)
4. \(30\)
Subtopic: Lenses |
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Five persons \({P}_1, {P}_2, {P}_3,{P}_4\) and \(P_5 \) recorded object distance \((u)\) and image distance \((v)\) using same convex lens having power \(+5~\text{D}\) as \((25,96), (30,62), (35,37), (45,35) \) and \((50,32)\) respectively. Identify correct statement:
| 1. | Reading recorded by all persons are correct |
| 2. | Reading recorded by \(P_3\) persons are incorrect |
| 3. | Reading recorded by \(P_3\) and \(P_2\) persons are incorrect |
| 4. | Reading recorded by \( P_4\) and \(P_5\) persons are incorrect |
Subtopic: Lenses |
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A convex lens of focal length \(30~\text{cm}\) is placed in contact with a concave lens of focal length \(20~\text{cm}.\) An object is placed at \(20~\text{cm}\) to the left of this lens system. The distance of the image from the lens in \(\text{cm}\) is:
1. \(30\)
2. \(45\)
3. \(\dfrac{60}{7}\)
4. \(15\)
1. \(30\)
2. \(45\)
3. \(\dfrac{60}{7}\)
4. \(15\)
Subtopic: Lenses |
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Two thin convex lenses of focal lengths \(30~\text{cm} \) and \(10~\text{cm} \) are placed coaxially \(10~\text{cm} \) apart. The power of this combination is:
1. \(10~\text{D}\)
2. \(20~\text{D}\)
3. \(1~\text{D}\)
4. \(5~\text{D}\)
1. \(10~\text{D}\)
2. \(20~\text{D}\)
3. \(1~\text{D}\)
4. \(5~\text{D}\)
Subtopic: Lenses |
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A slanted object \(AB \) is placed on one side of convex lens as shown in the diagram. The image is formed on the opposite side. Angle made by the image with principal axis is:
1. \(-\alpha/2 ~\)
2. \(-\alpha ~\)
3. \(+45^\circ ~\)
4. \(-45^\circ ~\)
1. \(-\alpha/2 ~\)
2. \(-\alpha ~\)
3. \(+45^\circ ~\)
4. \(-45^\circ ~\)
Subtopic: Lenses |
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A photograph of a landscape is captured by a drone camera at a height of \(18 \text{ km} .\) The size of the camera film is \(2 \text { cm} \times 2 \text{ cm}\) and the area of the landscape photographed is \(400 \text { km}^2\). The focal length of the lens in the drone camera is -
1. \(1.8 \text { cm}\)
2. \(0.9 \text { cm}\)
3. \(2.8 \text { cm}\)
4. \(2.5 \text { cm}\)
1. \(1.8 \text { cm}\)
2. \(0.9 \text { cm}\)
3. \(2.8 \text { cm}\)
4. \(2.5 \text { cm}\)
Subtopic: Lenses |
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What is the relative decrease in focal length of a lens for an increase in optical power by \(0.1~\text D\) from \(2.5~\text D?\) [\(\text D\) stands for diopter]
1. \(0.1\)
2. \(0.01\)
3. \(0.04\)
4. \(0.40\)
1. \(0.1\)
2. \(0.01\)
3. \(0.04\)
4. \(0.40\)
Subtopic: Lenses |
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