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 |
61%
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 $$\text{cot} \frac{A}{2}.$$ The angle of minimum deviation is:
 1 $$180^\circ-3A$$ 2 $$180^\circ-2A$$ 3 $$90^\circ-A$$ 4 $$180^\circ+2A$$
Subtopic:  Prisms |
81%
From NCERT
NEET - 2015
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If the focal length of the objective lens is increased then the 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 $$A$$. One of its refracting surfaces is silvered. Light rays falling at an angle of incidence $$2{A}$$ 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. $$2\text{sin}A$$
2. $$2\text{cos}A$$
3. $$\frac{1}{2}\text{cos}A$$
4. $$\text{tan}A$$

Subtopic:  Prisms |
76%
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 $$\dfrac{R}{2(\mu_1-\mu_2)}$$ 2 $$\dfrac{R}{(\mu_1-\mu_2)}$$ 3 $$\dfrac{2R}{(\mu_2-\mu_1)}$$ 4 $$\dfrac{R}{2(\mu_1+\mu_2)}$$
Subtopic:  Lens Makers' Formula |
66%
From NCERT
AIPMT - 2013
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For a normal eye, the cornea of the eye provides a converging power of $$40~\text{D}$$ and the least converging power of the eye lens behind the cornea is $$20~\text{D}$$. Using this information, the distance between the retina and the cornea-eye lens can be estimated to be:
1. $$2.5~\text{cm}$$
2. $$1.67~\text{cm}$$
3. $$1.5~\text{cm}$$
4. $$5~\text{cm}$$

Subtopic:  Human Eye |
62%
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 |
79%
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. $$\frac{A}{\mu}$$
4. $$\frac{A}{2\mu}$$

Subtopic:  Prisms |
78%
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. $$2f_1+f_2$$
4. $$-2f_1+f_2$$

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 $$20~\text{cm}$$. The focal length of the lenses is:
1. $$10~\text{cm}, ~10~\text{cm}$$
2. $$15~\text{cm}, ~5~\text{cm}$$
3. $$18~\text{cm}, ~2~\text{cm}$$
4. $$11~\text{cm}, ~9~\text{cm}$$

Subtopic:  Telescope |
82%
From NCERT
AIPMT - 2012
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