# A plano-convex lens when silvered in the plane side behaves like a concave mirror of focal length 30 cm. However, when silvered on the convex side it behaves like a concave mirror of focal length 10 cm. Then the refractive index of its material will be  1. 3.0                                2. 2.0 3. 2.5                                4. 1.5

Subtopic:  Lenses |
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A ray of light travels from an optically denser to rarer medium. The critical angle for the

two media is C. The maximum possible deviation of the ray will be

1. $\left(\frac{\mathrm{\pi }}{2}-C\right)$

2. 2C

3. $\mathrm{\pi }-2\mathrm{C}$

4. $\mathrm{\pi }-\mathrm{C}$

Subtopic:  Total Internal Reflection |
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A point object is moving on the principal axis of a concave mirror of focal length $$24$$ cm towards the mirror. When it is at a distance of $$60$$ cm from the mirror, its velocity is $$9$$ cm/secWhat is the velocity of the image at that instant?
 1 $$5$$ cm/sec towards the mirror 2 $$4$$ cm/sec towards the mirror 3 $$4$$ cm/sec away from the mirror 4 $$9$$ cm/sec away from the mirror
Subtopic:  Reflection at Spherical Surface |
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A room (cubical) is made of mirrors. An insect is moving along the diagonal on the floor

such that the velocity of image of insect on two adjacent wall mirrors is . The

velocity of image of insect in ceiling mirror is

1. 10 $cm{s}^{-1}$

2. 20 $cm{s}^{-1}$

3. $\frac{10}{\sqrt{2}}cm{s}^{-1}$

4. $10\sqrt{2}cm{s}^{-1}$

Subtopic:  Reflection at Plane Surface |
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Figure shows a cubical room ABCD with the wall CD as a plane mirror. Each side of the

room is 3m. We place a camera at the midpoint of the wall AB. At what distance should

the camera be focussed to photograph an object placed at A

1. 1.5 m

2. 3 m

3. 6 m

4. More than 6 m

Subtopic:  Reflection at Plane Surface |
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If an object moves towards a plane mirror with a speed v at an angle $\theta$ to the

perpendicular to the plane of the mirror, find the relative velocity between the object and

the image

1. v

2. 2v

3. 2v cos $\theta$

4. 2v sin $\theta$

Subtopic:  Reflection at Plane Surface |
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To an astronaut in a spaceship, the sky appears:

(1) Black

(2) White

(3) Green

(4) Blue

Subtopic:  Human Eye |
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A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle $\theta$, the spot of light is found to move through a distance y on the scale. The angle $\theta$ is given by

(1) $\frac{y}{2x}$

(2) $\frac{y}{x}$

(3) $\frac{x}{2y}$

(4) $\frac{x}{y}$

Subtopic:  Reflection at Plane Surface |
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NEET - 2017
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Two identical glass $\left({\mu }_{g}=3/2\right)$ equi-convex lenses of focal length $f$ each are kept in contact. The space between the two lenses is filled with water $\left({\mu }_{w}=4/3\right)$. The focal length of the combination is

(a)  $f/3$             (b) $f$

(c) $\frac{4f}{3}$               (d) $\frac{3f}{4}$

Subtopic:  Lenses |
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From NCERT
NEET - 2016
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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 |
70%
From NCERT
NEET - 2016
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