The chromatic Aberration in lenses becomes due to ____.
dissimilarity of main axis of rays
dissimilarity of radii of curvature
variation of focal length of lenses with wavelength
None of the above
If aperture of lens is halved then image is ____.
no effect on size
intensity of image decreases
both A and B
None of the above
When the convergent nature of a convex lens is less as compared with air ____.
in water
in oil
in both
None of the above
An achromatic combination of lenses produces ____.
colored images
highly enlarged image
images in black and white
images unaffected by variation of refractive index with wavelength
In a parallel beam of white light is incident on a converging lens, the color which is brought to focus nearest to the lens is :
violet
red
the mean color
All the colors together
A magnifying glass is to be used at the fixed object distance of 1 inch. If it is to produce an erect image magnified 5 times its focal length should be____.
0.2 inch
0.8 inch
1.25 inch
5 inch
A film projector magnifies a 100 cm2 film strip on a screen. If the linear magnification is 4, the area of magnified film on the screen is ____.
1600 cm2
400 cm2
800 cm2
200 cm2
An object placed 10 cm in front of a lens has an image 20 cm behind the lens. What is the power of the lens (in dioptres) ____.
1.5
3.0
– 15.0
+ 15.0
A beam of parallel rays is brought to a focus by a Plano-convex lens. A thin concave lens of the same focal length is joined to the first lens. The effect of this is ____.
the focal point shifts away from the lens by a small distance
the focus remains undisturbed
the focus shifts to infinity
the focal point shifts towards the lens by a small distance
A thin plano-convex lens acts like a concave mirror of focal length 0.2 m when silvered from its plane surface. The refractive index of the material of the lens is 1.5. The radius of curvature of the convex surface of the lens is ____.
0.4 m
0.2 m
0.1 m
0.75 m
A point object is placed at the center of a glass sphere of radius 6 cm and refractive index 1.5. The distance of the virtual image from the surface of the sphere is ____.
2 cm
4 cm
6cm
12 cm
In order to obtain a real image of magnification 2 using a converging lens of focal length 20 cm, where should an object be placed?
50 cm
30 cm
– 50 cm
– 30 cm
A plano-convex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object is placed in order to have a real image of the size of the object?
20 cm
30 cm
60 cm
80 cm
/
10 cm
20 cm
40 cm
15 cm
At what distance from a convex lens of focal length 30 cm, an object should be placed so that the size of the image be 1/2 of the object?
30 cm
60 cm
15 cm
90 cm
A Plano-convex lens is made of refractive index of 1.6. The radius of curvature of the curved surface is 60 cm. The focal length of the lens is ____.
400 cm
200 cm
100 cm
50 cm
The radius of the convex surface of Plano-convex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length of the lens is ____.
30 cm
50 cm
20 cm
40 cm
A combination of two thin convex lenses of focal length 0.3 m and 0.1 m will have minimum spherical and chromatic aberrations if the distance between them is ____.
0.1 m
0.2 m
0.3 m
0.4 m
A bi-convex lens made of glass (refractive index 1.5) is put in a liquid of refractive index 1.7. Its focal length will ____.
decrease and change sign
increase and change sign
decrease and remain of the same sign
increase and remain of the same sign
Spherical aberration in a lens ____.
is minimum when most of the deviation is at the first surface
is minimum when most of the deviation is at the second surface
is minimum when the total deviation is equally distributed over the two surface
Does not depend on the above consideration