In an astronomical telescope in normal adjustment, a straight line of length $$L$$ is drawn on the inside part of the objective lens. The eye-piece forms a real image of this line. The length of this image is $$l.$$ The magnification of the telescope is:
1. $$\frac{L}{l}+1$$
2. $$\frac{L}{l}-1$$
3. $$\frac{L+1}{l-1}$$
4. $$\frac{L}{l}$$

Subtopic:  Telescope |
58%
From NCERT
NEET - 2015
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A beam of light consisting of red, green, and blue colours is incident on a right-angled prism. The refractive index of the material of the prism for the red, green, and blue wavelengths is $$1.39$$, $$1.44$$, and $$1.47$$ respectively.

The prism will:

 1 separate the blue colour part from the red and green colour 2 separate all the three colours from one another 3 not separate the three colours at all 4 separate the red colour part from the green and blue colours
Subtopic:  Prisms |
62%
From NCERT
NEET - 2015
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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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The reddish appearance of the sun at sunrise and sunset is due to:
 1 the scattering of light. 2 the polarisation of light. 3 the colour of the sun. 4 the colour of the sky.
Subtopic:  Total Internal Reflection |
89%
From NCERT
NEET - 2013
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Two plane mirrors are inclined at $$70^\circ.$$ A ray incident on one mirror at an angle, $$\theta$$ after reflection falls on the second mirror and is reflected from there parallel to the first mirror. The value of $$\theta$$ is:
1. $$45^\circ$$
2. $$30^\circ$$
3. $$55^\circ$$
4. $$50^\circ$$
Subtopic:  Reflection at Plane Surface |
55%
From NCERT
NEET - 2013