Types of Lenses
Trending Questions
Q. A biconvex lens has a radius of curvature of magnitude 20 cm and the refractive index of the lens is 1.5. Which of the following option describe best the image formed of an object of height 2 cm placed 30 cm from the lens?
- Real, inverted, height =1 cm
- Virtual, upright, height =1 cm
- Virtual, upright, height =0.5 cm
- Real, inverted, height =4 cm
Q. The power of a thin bi-convex lens is P. The lens is cut horizontally along its principle axis into two equal parts and then both the parts are placed in close contact as shown in the figure. The power of combination will be:
- P
- 2P
- P2
- Zero
Q. An equiconvex lens has power P and radii of curvature R. The radius of curvature of the surface of a plano-convex lens made of the same material with power 1.5P is
- 2R
- 3R
- R3
- R2
Q.
Locate the image formed by refraction in the situation shown in figure.
Q. A concave lens is converging lens.( )
- True
- False
- Depends on situation
Q. An achromatic telescope objective is to be made by combining the lenses of flint and crown glasses. The proper choice is-
- Convergent of crown and divergent of flint
- Divergent of crown and convergent of flint
- Both divergent
- Both convergent
Q. A lens behaves as a convergent lens in air and a diverging lens in water. the refractive index of the material of the lens is
- Equal to 43
- Equal to unity
- Between unity and 43
- Greater than 43
Q. Two lenses in contact form an achromatic lens, Their focal lengths are in the ratio 2:3. Their disperive powers must be in the ratio of
- 1:3
- 2:3
- 3:2
- 3:1
Q. One face of a rectangular glass plate of thickness 6 cm is silvered. an object is placed at a distance of 8 cm in front of the unsilvered face. Its image is formed 10 cm behind the silvered face. The refractive index of glass plate is :
- 53
- 43
- 76
- 32
Q. A double convex lens, made of a material of refractive index μ1, is placed inside two liquids of refractive indices mu2andμ3 as shown. mu2>mu1>mu3. A wide, parallel beam of light is incident on the lens from the left. The lens will give rise to
- a single convergent beam
- two different convergent beams
- two different divergent beams
- a convergent and a divergent beam.
Q. The power of a biconvex lens is 10 dioptre and the radius of curvature of each surface is 10 cm. Then the refractive index of the material of the lens is :
- 98
- 53
- 32
- 43
Q. The given lens is broken into four parts rearranged as shown. If the initial focal length is f, then after rearrangement the equivalent focal length is
- f/2
- f/4
- 4f
- f
Q. Simplify (2root3) (3+root5)??
Q. A doctor has prescribed a corrective lens of power +1.5D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
Q. A convex glass lens (refractive index= 1.5) has a focal length of 8cm when placed in air. what is the focal length of the lens when it is immersed in water?(refractive index=4/3)
Q. Two thin symmetrical lenses of different nature and of different material have equal radii of curvature R=15 cm. The lenses are put close together and immersed in water (μw=4/3). The focal length of the system in water is 30 cm. The difference between refractive indices of the two lenses is
- 1/2
- 1/4
- 1/3
- 3/4
Q. A thin equiconvex lens of refractive index 3/2 is placed on a horizontal plane mirror as shown in figure. The space between the lens and the mirror is filled with a liquid of refractive index 4/3. It is found what when a point object is placed 15 cm above the lens on its principal axis, the object coincides with its own image.
If another liquid is filled instead of water, the object and the image coincide at a distance 25 cm from the lens. Calculate the refractive index of the liquid.
If another liquid is filled instead of water, the object and the image coincide at a distance 25 cm from the lens. Calculate the refractive index of the liquid.
- 1.6
- 2.6
- 2.8
- 3.2
Q. In a lake, a fish rising vertically to the surface of water uniformly at the rate of 3 m/s, observes a bird diving vertically towards the water at a rate of 9 m/s vertically above it. the actual velocity of the dive of the bird is : (Given refractive index water =4/3)
- 9.2 m/s
- 4.5 m/s
- 9.0 m/s
- 3.2 m/s
Q. The radiation emitted by a star A is 1000 times that of the sun. If the surface temperatures of the sun and star A are 6000K and 2000K, respectively, the ratio of the radii of the star A and the Sun is:
- 300:1
- 600:1
- 900:1
- 1200:1
Q. A thin equiconvex glass lens (μg=1.5) is being placed on the top of a vessel of height h=20 cm as shown in fig. A luminous point source is being placed at the bottom of vessel on the principal axis of the lens. When the air is on both the side of the lens the image of luminous source is formed at a distance of 20 cm from the lens out side the vessel. When the air inside the vessel is being replaced by a liquid of refractive index μ1, the image of the same source is being formed at a distance 30 cm from the lens outside the vessel. If μ1 is approximately x100. Find x.
Q. Figure (a) shows two plano-convex lenses in contact as shown. The combination has focal length 24 cm. Figure (b) shows the same with a liquid introduced between them. If refractive index of glass of the lenses is 1.50 and that of the liquid is 1.60, the focal length of system in Fig. (b) will be
- 120cm
- −120cm
- −24cm
- 24cm
Q. Three observers A, B and C measure the speed of light coming from a source as vA, vB and vC. Observer A moves towards the source, C moves away from source and B stays stationary. The surrounding medium is water. If A and C are moving at the same speed, then
- vA>vB>vC
- vA<vB<vC
- vA=vB=vC
- vB=12(vC+vA)
Q. A thin plano - convex lens fits exactly into a thin plano - concave lens. Their plane surfaces are parallel to each other. If the lenses are made of different materials of refractive indices μ1 and μ2 and R is the radius of curvature of the curved surfaces of the lenses, then the focal length of the combination is :
- Rμ2−μ1
- R2−(μ1+μ2)
- 2Rμ2−μ1
- R2(μ1−μ2)
Q. A bird flies down vertically towards a water surface. For a fish inside water, vertically below the bird, the bird will appear
- to be farther away than the actual distance.
- to be closer than the actual distance.
- to move faster than its actual speed
- to move slower than lts actual speed.
Q. The power of a thin convex lens (ng=1.5) is +5.0D, when this lens is dipped in a liquid of refractive index nl, it behaves like a concave lens whose focal length is 100 cm, then what will be the value of nl?
Q. Assertion :The focal length of a lens does not depend on the medium in which it is submerged. Reason: 1f=μ2−μ1μ1(1R1−1R2)
- Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
- Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
- Assertion is correct but Reason is incorrect
- Assertion is incorrect but Reason is correct
Q. A lens that has convex surface at one side and concave surface at another side behaves as :
a) convergent lens when the radius of curvature of convex surface is greater than that of concave surface.
b) divergent lens when the radius of curvature of concave surface is greater than that of convex surface.
c) convergent lens when the radius of curvature of convex surface is less than that of concave.
d) divergent lens when the radius of curvature of concave surface is less than that of convex surface.
b) divergent lens when the radius of curvature of concave surface is greater than that of convex surface.
c) convergent lens when the radius of curvature of convex surface is less than that of concave.
d) divergent lens when the radius of curvature of concave surface is less than that of convex surface.
- a, b are true
- a, d are true
- c, d are true
- b, c are true
Q. Assertion :An air bubble in water diverges light. Reason: A lens is a diverging lens if after refraction light incident on it diverge and not really meet after refraction.
- Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
- Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
- Assertion is correct but Reason is incorrect
- Both Assertion and Reason are incorrect
Q. The lens of a telescope, after focussing for infinity is taken out and a slit of length L, is placed in its position. A sharp image of the slit is formed by the eyepiece at a certain distance from it on other side. The length of the image is l, so the magnification of the telescope is
- 2L1
- L21
- Ll
- 1l
Q. A convex lens of focal length f is placed somewhere in between the object and a screen. The distance between object and screen is x. If magnification produced is m, the focal length of the lens is:
- mx(m−1)2
- (m+1)2mx
- (m−1)2mx
- mx(m+1)2