# A concave mirror gives an image three times as large as the object placed at a distance of 20 cm from it. For the image to be real, the focal length should be: 1. 10 cm 2. 15 cm 3. 20 cm 4. 30 cm

Subtopic:  Reflection at Spherical Surface |
61%
From NCERT
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If the focal length of the objective lens is increased, then magnifying power of:

 1 microscope will increase but that of telescope decrease 2 microscope and telescope both will increase 3 microscope and telescope both will decrease 4 microscope will decrease but that of the telescope will increase
Subtopic:  Simple & Compound Microscope |
67%
From NCERT
AIPMT - 2014
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An air bubble in a glass slab with refractive index 1.5 (near-normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is:

 1 8 2 10 3 12 4 16
Subtopic:  Refraction at Plane Surface |
74%
From NCERT
NEET - 2016
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Choose the correct mirror image of the figure:

 1 2 3 4
Subtopic:  Reflection at Plane Surface |
77%
From NCERT
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A mark on the surface of sphere (µ = 3/2) is viewed from a diametrically opposite position. It appears to be at a distance $$15~\mathrm{cm}$$ from its actual position. The radius of sphere is:
1. 15 cm
2. 5 cm
3. 7.5 cm
4. 2.5 cm

Subtopic:  Refraction at Curved Surface |
53%
From NCERT
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A concave lens of focal length 25 cm produces an image $\frac{1}{10}\mathrm{th}$ the size of the object. The distance of the object from the lens is:

1. 225 cm

2. 250 cm

3. 150 cm

4. 175 cm

Subtopic:  Lenses |
82%
From NCERT
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Focal lengths of objective and eyepiece of a compound microscope are 2 cm and 6.25 cm respectively. An object AB is placed at a distance of 2.5 cm from the objective which forms the image A'B' as shown in the figure. Maximum magnifying power in this case, will be:

 1 10 2 20 3 5 4 25
Subtopic:  Simple & Compound Microscope |
68%
From NCERT
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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.

Subtopic:  Lenses |
62%
From NCERT
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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 cm, where $$F_1$$ and $$F_2$$ are foci of the lens. The value of $$x'$$ is:

 1 10 cm 2 20 cm 3 30 cm 4 40 cm
Subtopic:  Lenses |
72%
From NCERT
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In the following diagram, what is the distance x if the radius of curvature is R = 15 cm?

1. 30 cm

2. 20 cm

3. 15 cm

4. 10 cm

Subtopic:  Refraction at Curved Surface |
78%
From NCERT
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