Q. No.A convex lens is made from glass material having refractive index of \(1.4\) with same radius of curvature on both sides. The ratio of its focal length and radius of curvature is:
1. \(0.5\)
2. \(2.5\)
3. \(0.8\)
4. \(1.25\)
1. \(0.5\)
2. \(2.5\)
3. \(0.8\)
4. \(1.25\)
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If sunlight is focused on a paper using convex lens, it starts burning the paper in shortest time when the lens is kept at \(30~\text{cm}\) above the paper. If the radius of curvature of the lens is \(60~\text{cm}\) then the refractive index of the lens material is \(\dfrac {\alpha}{10}.\) \(\alpha\)
1. \(10\)
2. \(20\)
3. \(30\)
4. \(40\)
1. \(10\)
2. \(20\)
3. \(30\)
4. \(40\)
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A thin biconvex lens is prepared from the glass (\(\mu=1.5\))
1. \(10\)
2. \(12.5\)
3. \(13\)
4. \(13.5\)
1. \(10\)
2. \(12.5\)
3. \(13\)
4. \(13.5\)
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The magnitudes of power of a biconvex lens (refractive index \(1.5\)) and that of a plano-concave lens (refractive index \(=~1.7\)) are same. If the curvature of plano-concave lens exactly matches with the curvature of back surface of the biconvex lens, then ratio of radius curvature of front and back surface of of the biconvex lens is:
1. \(5:2\)
2. \(5:12\)
3. \(12:5\)
4. \(2:5\)
1. \(5:2\)
2. \(5:12\)
3. \(12:5\)
4. \(2:5\)
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A convex lens of refractive index \(1.5\) and focal length \(f = 18~\text{cm}\) is immersed in water. The difference in focal lengths of the given lens when it is in water and in air is \(\alpha \times f\). The value of \(\alpha\) is: (refraction index of water \(= \dfrac{4}{3}\))
1. \(3\)
2. \(2\)
3. \(5\)
4. \(7\)
1. \(3\)
2. \(2\)
3. \(5\)
4. \(7\)
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A biconvex lens is formed by using two thin planoconvex lenses, as shown in the figure. The refractive index and radius of curved surfaces are also mentioned in figure. When an object is placed on the left side of lens at a distance of \(30~\text{cm}\) from the biconvex lens, the magnification of the image will be:
1. \(-2\)
2. \(+2\)
3. \(+2.5\)
4. \(-2.5\)
1. \(-2\)
2. \(+2\)
3. \(+2.5\)
4. \(-2.5\)
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Light from a point source in air falls on a spherical glass surface (refractive index, \(\mu = 1.5 \) and radius of curvature \(= 50 ~\text{cm}\)). The image is formed at a distance of \(200 ~\text{cm}\) from the glass surface inside the glass. The magnitude of distance of the light source from the glass surface is: (in m)
1. \(4\)
2. \(29 \)
3. \(16 \)
4. \(17\)
1. \(4\)
2. \(29 \)
3. \(16 \)
4. \(17\)
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A concave-convex lens of refractive index \(1.5\) and the radii of curvature of its surfaces are \(30~\text{cm} \) and \(20~\text{cm}\) respectively. The concave surface is upwards and is filled with a liquid of refractive index \(1.3.\) The focal length of the liquid-glass combination will be:
1. \(\dfrac{500}{11}~\text{cm}\)
2. \(\dfrac{800}{11}~\text{cm}\)
3. \(\dfrac{700}{11}~\text{cm}\)
4. \(\dfrac{600}{11}~\text{cm}\)
1. \(\dfrac{500}{11}~\text{cm}\)
2. \(\dfrac{800}{11}~\text{cm}\)
3. \(\dfrac{700}{11}~\text{cm}\)
4. \(\dfrac{600}{11}~\text{cm}\)
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The radii of curvature for a thin convex lens are \(10 ~\text{cm}\) and \(15 ~\text{cm}\) respectively. The focal length of the lens is \(12 ~\text{cm.}\) The refractive index of the lens material is:
1. \(1.2\)
2. \(1.4\)
3. \(1.5\)
4. \(1.8\)
1. \(1.2\)
2. \(1.4\)
3. \(1.5\)
4. \(1.8\)
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A lens having refractive index. \(1.6 \) has focal length of \(12~\text{cm},\) when it is in air. Find the focal length of the lens when it is placed in water: (Take refractive index of water as \(1.28\))
1. \(355~\text{mm}\)
2. \(288~\text{mm}\)
3. \(555~\text{mm}\)
4. \(655~\text{mm}\)
1. \(355~\text{mm}\)
2. \(288~\text{mm}\)
3. \(555~\text{mm}\)
4. \(655~\text{mm}\)
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