Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens when immersed in a liquid of refractive index of 1.25 will be :
10cm
2.5 cm
5 cm
7.5 cm
A man is 6 ft tall. In order to see his entire image, he requires a plane mirror of minimum length equal to :
6 ft
12 ft
2 ft
3 ft
For the given incident ray as shown in figure, the condition of total internal reflection of the ray will be satisfied if the refractive index of block will be:
One face of a rectangular glass plate 6 cm thick is silvered. An object held 8 cm in front of the first face, forms an image 12 cm behind the silvered face. The refractive index of the glass is :
0.4
0.8
1.2
1.6
If fv and fn are the focal lengths of a convex lens for violet ad red light respectively and FV and FR are the focal lengths of concave lens for violet and red light respectively, then we have :
fV < fR and FV > FR
fV < fR and FV < FR
fV > fR and FV > FR
fV > fR and FV < FR
The hypermetropia is a
short-sight defect
long-sight defect
bad vision due to old age
None of the above
A convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together. What will be their resulting power?
+ 6.5 D
- 6.5 D
+7.5 D
-0.75 D
A telescope has an objective lens of 10cm diameter and is situated at a distance of one kilometre from two objects. Find out the minimum distance between these two objects, which can be resolved by the telescope, when the mean wavelength of light is 5000 Å.
0.5 m
5 m
5 mm
A lens is placed between a source of light and a wall. It forms images of area A1 and A2 on the wall, for its two different positions the area of the source of light is :
