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Q. No.When a concave mirror of focal length \(f\) is immersed in water, its focal length becomes \(f',\) then:
1.
\(f' = f\)
2.
\(f'<f\)
3.
\(f'>f\)
4.
The information is insufficient to predict
Subtopic: Reflection at Spherical Surface |
71%
Level 2: 60%+
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An object is at a distance of \(30\) cm in front of a concave mirror of focal length \(10\) cm. The image of the object will be:
| 1. | smaller in size. |
| 2. | inverted. |
| 3. | between the focus and centre of curvature. |
| 4. | All of the above. |
Subtopic: Reflection at Spherical Surface |
87%
Level 1: 80%+
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To a diver inside water, the setting sun will appear at an angle (with the horizontal) of: \(\left[ \mu_w = \frac{5}{4} \right]\)
| 1. | \(53^{\circ}\) | 2. | \(37^{\circ}\) |
| 3. | \(45^{\circ}\) | 4. | \(60^{\circ}\) |
Subtopic: Total Internal Reflection |
Level 3: 35%-60%
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A spherical fishbowl of radius \(15\) cm is filled with water of refractive index \(\frac{4}{3}.\) A cat standing outside in the air at a distance of \(30\) cm from the centre of the fishbowl is looking at the fish. At what distance from the centre would the cat appear to the fish situated at the centre?
| 1. | \(45\) cm | 2. | \(30\) cm |
| 3. | \(15\) cm | 4. | \(25\) cm |
Subtopic: Refraction at Curved Surface |
51%
Level 3: 35%-60%
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Two convex lenses of focal length \(X\) and \(Y\) are placed parallel to each other. An object at infinity from the first lens forms its image at infinity from the second lens. The separation between the two lenses should be:
| 1. | \(X+Y\) | 2. | \(\dfrac{X +Y}{2}\) |
| 3. | \(X-Y\) | 4. | \(\dfrac{X -Y}{2}\) |
Subtopic: Lenses |
69%
Level 2: 60%+
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A plane mirror is placed at the bottom of a fish tank filled with water of refractive index \(\dfrac{4}{3}.\) The fish is at a height \(10~\text{cm}\) above the plane mirror. An observer \(O\) is vertically above the fish outside the water. The apparent distance between the fish and its image is:
| 1. | \(15\text{cm}\) | 2. | \(30~\text{cm}\) |
| 3. | \(35~\text{cm}\) | 4. | \(45~\text{cm}\) |
Subtopic: Refraction at Plane Surface |
64%
Level 2: 60%+
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A liquid of refractive index \(\frac{4}{3}\) is placed between two identical planoconvex-lenses touching each other at their spherical surfaces of radius \(R\). If the refractive index of the lens is \(1.50\), then the lens behaves as:
| 1. | a convergent with power \(P=\frac{1}{3 R}\) |
| 2. | a convergent with power \(P=\frac{1}{6 R}\) |
| 3. | a divergent with power \(P=\frac{1}{3 R}\) |
| 4. | a divergent with power \(P=\frac{1}{6 R}\) |
Subtopic: Lenses |
60%
Level 2: 60%+
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If there is no emergent light through a prism of refracting angle \(60^{\circ},\) whatever may be the angle of incidence, then the minimum value of the refractive index of the material of the prism is:
| 1. | \(2\) | 2. | \(\sqrt{2}\) |
| 3. | \(1.5\) | 4. | \(\sqrt{3}\) |
Subtopic: Prisms |
55%
Level 3: 35%-60%
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The Refractive index of material of an equilateral prism is \(\sqrt{2}\). Angle of incidence for minimum deviation is:
1. \(60^{\circ}\)
2. \(45^{\circ}\)
3. \(30^{\circ}\)
4. \(15^{\circ}\)
1. \(60^{\circ}\)
2. \(45^{\circ}\)
3. \(30^{\circ}\)
4. \(15^{\circ}\)
Subtopic: Prisms |
73%
Level 2: 60%+
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The minimum magnifying power of an astronomical telescope is \(40\). If the length of the telescope is \(205\) cm, then the focal length of its field lens is:
1. \(5\) cm
2. \(200\) cm
3. \(40\) cm
4. \(140\) cm
Subtopic: Telescope |
66%
Level 2: 60%+
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