# Two identical thin plano-convex glass lenses (refractive index = 1.5) each having radius of curvature of 20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of a refractive index of 1.7. The focal length of the combination is: 1. -20 cm 2. -25 cm 3. -50 cm 4. 50 cm

Subtopic:  Lens Makers' Formula |
59%
From NCERT
NEET - 2015
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The refracting angle of a prism is $$A,$$ and the refractive index of the material of the prism is $$cot \frac{A}{2}.$$ The angle of minimum deviation is:
1. $$180^\circ-3A$$
2. $$180^\circ-2A$$
3. $$90^\circ-A$$
4. $$180^\circ+2A$$
Subtopic:  Prisms |
80%
From NCERT
NEET - 2015
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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 the 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 |
70%
From NCERT
AIPMT - 2014
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The angle of a prism is $$\text{A}.$$ One of its refracting surfaces is silvered. Light rays falling at an angle of incidence $$2\text{A}$$ on the first surface return back through the same path after suffering reflection at the silvered surface. The refractive index $$\mu,$$ of the prism, is:
1. 2sinA

2. 2cosA

3. $\frac{1}{2}$cosA

4. tanA

Subtopic:  Prisms |
75%
From NCERT
AIPMT - 2014
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A plano-convex lens fits exactly into a plano-concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices $$\mu_1$$ and $$\mu_2$$ and $$R$$ is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is:
1. $$\frac{R}{2(\mu_1-\mu_2)}$$

2. $$\frac{R}{(\mu_1-\mu_2)}$$

3. $$\frac{2R}{(\mu_2-\mu_1)}$$

4. $$\frac{R}{2(\mu_1+\mu_2)}$$
Subtopic:  Lens Makers' Formula |
65%
From NCERT
AIPMT - 2013
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For a normal eye, the cornea of the eye provides a converging power of 40 D and the least converging power of the eye lens behind the cornea is 20 D. Using this information, the distance between the retina and the cornea-eye lens can be estimated to be:
1. 2.5 cm
2. 1.67 cm
3. 1.5 cm
4. 5 cm

Subtopic:  Human Eye |
63%
From NCERT
AIPMT - 2013
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When a biconvex lens of glass having a refractive index of 1.47 is dipped in a liquid, it acts as a plane sheet of glass. The liquid must have a refractive index:

1. equal to that of glass.

2. less than one.

3. greater than that of glass.

4. less than that of glass.

Subtopic:  Lens Makers' Formula |
78%
From NCERT
AIPMT - 2012
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A ray of light is incident at an angle of incidence, i, on one face of a prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is $\mu$, the angle of incidence i, is nearly equal to:

1. $\mu$A

2. $\frac{\mu A}{2}$

3. $A/\mu$

4. $A/2\mu$

Subtopic:  Prisms |
75%
From NCERT
AIPMT - 2012
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A concave mirror of the focal length ${f}_{1}$ is placed at a distance of d from a convex lens of focal length ${f}_{2}$. A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity. The distance d must be equal to:

1. ${f}_{1}+{f}_{2}$

2. $-{f}_{1}+{f}_{2}$

3. $2{f}_{1}+{f}_{2}$

4. $-2{f}_{1}+{f}_{2}$

Subtopic:  Reflection at Spherical Surface |
From NCERT
AIPMT - 2012
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The magnifying power of a telescope is 9. When it is adjusted for parallel rays the distance between the objective and eyepiece is 20 cm. The focal length of the lenses is:

1. 10 cm, 10 cm

2. 15 cm, 5 cm

3. 18 cm, 2 cm

4. 11 cm, 9 cm

Subtopic:  Telescope |
81%
From NCERT
AIPMT - 2012
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