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 |
70%
From NCERT
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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 |
86%
From NCERT
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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 |
From NCERT
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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%
From NCERT
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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 $$\frac{X + Y}{2}$$ 3 X - Y 4 $$\frac{X - Y}{2}$$
Subtopic:  Lenses |
68%
From NCERT
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A plane mirror is placed at the bottom of a fish tank filled with water of refractive index $\frac{4}{3}$. The fish is at a height 10 cm above the plane mirror. An observer O is vertically above the fish outside water. The apparent distance between the fish and its image is:

1. 15 cm

2. 30 cm

3. 35 cm

4. 45 cm

Subtopic:  Refraction at Plane Surface |
63%
From NCERT
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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 $$\mathrm{P}=\frac{1}{3 R}$$ 2 a convergent with power $$\mathrm{P}=\frac{1}{6 R}$$ 3 a divergent with power $$\mathrm{P}=\frac{1}{3 R}$$ 4 a divergent with power $$\mathrm{P}=\frac{1}{6 R}$$

Subtopic:  Lenses |
59%
From NCERT
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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 |
53%
From NCERT
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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. $$15^{\circ}$$

Subtopic:  Prisms |
72%
From NCERT
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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 |
67%
From NCERT
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