The magnifying power of a telescope is 9. When it is adjusted for parallel rays the distance between the objective and eyepiece is 20 cm. The focal length of lenses are

10 cm, 10 cm
15 cm, 5cm
18 cm, 2 cm
11 cm, 9cm

Solution

A concave mirror of focal length ‘f₁’ is placed at a distance of ‘d’ from a convex lens of focal length ‘f₂’. A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity.The distance ‘d’ must be equal to

f₁ + f₂
–f₁ + f₂
2f₁+ f₂
–2f₁+ f₂

Solution

d= f₁ + 2f₂

A ray of light is incident at an angle of incidence, i, on one face of prism of angle A(assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is m, the angle of incidence i, is nearly equal to

μA
^μA⁄₂
^A⁄_μ
^A⁄_2μ

Solution

For normally emerge e = 0

Therefore r₂= 0 and r₁ = A

Snell’s Law for Incident ray’s

1sin i= μ sin r₁= μ sin A

For small angle

i= μA

When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid,it acts as a plane sheet of glass. This implies that the liquid must have refractive index

equal to that of glass
less than one
greater than that of glass
less than that of glass

For the angle of minimum deviation of a prism to be equal to its refracting angle, the prism must be made of a material whose refractive index

lies between √2 and 1
lies between 2 and √2
is less than 1
is greater than 2

Solution

A thin prism of angle 15º made of glass of refractive index µ₁= 1.5 is combined with another prism of glass of refractive index µ₂= 1.75. The combination of the prism produces dispersion without deviation. The angle of the second prism should be

7°
10°
12°
5°

Solution

A biconvex lens has a radius of curvature of magnitude 20cm. Which one of the following options best describe the image formed of an object of height 2 cm placed 30 cm from the lens?

Virtual, upright, height = 1 cm
Virtual, upright, height= 0.5 cm
Real, inverted, height = 4 cm
Real,inverted, height = 1 cm

Solution

A ray of light travelling in a transparent medium of refractive index m, falls on a surface separating the medium from air at an angle of incidence of 45°. For which of the following value of m the ray can undergo total internal reflection?

μ= 1.33
μ= 1.40
μ= 1.50
μ= 1.25

Solution

Two thin lenses of focal lengths f₁ and f₂ are in contact and coaxial. Its power is same as power of a single lens given by

\(\frac{f_{1}+f_{2}}{f_{1}f_{2}}\)
\(\sqrt{\left ( \frac{f_{1}}{f_{2}} \right )}\)
\(\sqrt{\left ( \frac{f_{2}}{f_{1}} \right )}\)
\(\frac{f_{1}+f_{2}}{2}\)

Solution

A telescope has an objective lens of 10 cm diameter and is situated at a distance of one kilometer from two objects.The minimum distance between these two objects, which can be resolved by the telescope, when the mean wave length of light is 5000 Å, is of the order of

5 cm
0.5 m
5 m
5 mm

Solution

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