The frequency of a light wave in a material is 2 × 10¹⁴Hz and wavelength is 5000 Å. The refractive index of material will be

1.50
3.00
1.33
1.40

Solution

An object is placed at a distance of 40 cm in front of a concave mirror of focal length 20 cm. The image produced is

real, inverted and smaller in size
real, inverted and of same size
real and erect
virtual and inverted

Solution

The wavelength of a monochromatic light in vacuum is l. It travels from vacuum to a medium of absolute refractive indexµ. The ratio of wavelength of the incident and refracted wave is

µ²: 1
1 : 1
µ: 1
1 : µ

The refractive indices of glass and water with respect to air are 3/2 and 4/3 respectively. Then the refractive index of glass with respect to water is

Solution

Two convex lenses of focal lengths 0.3 m and 0.05 m are used to make a telescope.The distance kept between the two in order to obtain an image at infinity is

0.35 m
0.25 m
0.175 m
0.15 m

Solution

In a telescope, to obtain an image at infinity or in normal adjustment, the distance between two convex lenses one called objective (greater focal length) and the other called eye piece (shorter focal length) is L.L = f₀ + f_e= 0.3 + 0.05 = 0.35 m.

Why is refractive index in a transparent medium greater than one ?

Because the speed of light in vaccum is always less than speed in a transparent medium
Because the speed of light in vaccum is always greater than speed in a transparent medium
Frequency of wave changes when it crosses medium
None of these

If D is the deviation of a normally falling light beam on a thin prism of angle A and dis the dispersive power of the same prism then

D is independent of A.
D is independent of refractive Index.
dis independent of refractive index.
dis independent of A.

Two convex lenses of focal lengths f₁ and f₂ are mounted coaxially separated by a distance. If the power of the combination is zero, the distance between the lenses is

\(\left | f_{1}-f_{2} \right |\)
f₁ + f₂
\(\frac{f_{1}f_{2}}{\left | f_{1}-f_{2} \right |}\)
\(\frac{f_{1}f_{2}}{f_{1}+f_{2}}\)

A plano-convex lens of focal length 30 cm has its plane surface silvered. An object is placed 40 cm from the lens on the convex side. The distance of the image from the lens is

18 cm
24 cm
30 cm
40 cm

A real image is formed by a convex lens. If we put a concave lens in contact with it, the combination again forms a real image. The new image

is closer to the lens system.
is farther form the lens system.
is at the original position.
may be any where depending on the focal length of the concave lens.

Solution

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