Ray Optics and Optical Instruments

A 2.0 cm object is placed 15 cm in front of a concave mirror of focal length 10 cm. What is the size and nature of the image ?

• 4 cm, real

• 4 cm, virtual

• 1.0 cm, real

• None of these

A beam of monochromatic blue light of wavelength 4200 $\stackrel{\circ }{\mathrm{A}}$ in air travels in water of refractive index 4/3. Its wavelength in water will be.

• 4200 $\stackrel{\circ }{\mathrm{A}}$

• 5800 $\stackrel{\circ }{\mathrm{A}}$

• 4150 $\stackrel{\circ }{\mathrm{A}}$

• 3150 $\stackrel{\circ }{\mathrm{A}}$

A ray of light travelling inside a rectangular glass block of refractive index $\sqrt{2}$ is incident on the glass-air surface at an angle of incidence of 45°. Show that the ray will emerge into the air at an angle of refraction equal to 90°.

Two mirrors at an angle 0° produce 5 images of a point. The number of images produced when θ is decreased to θ − 30° is

• 9

• 10

• 11

• 12

The radius of the light circle observed by a fish at a depth of 12 m is (refractive index of water = 4/3)

• $36\sqrt{7}$

• $\frac{36}{\sqrt{7}}$

• $36\sqrt{5}$

• $4\sqrt{5}$

A plano-convex lens (f = 20 cm) is silvered at plane surface. Now focal length will be

• 20 cm

• 40 cm

• 30 cm

• 10 cm

If x₁ be the size of the magnified image and x₂ the size of the diminished image in Lens Displacement Method, then the size of the object is

• $\sqrt{{\mathrm{x}}_1{\mathrm{x}}_2}$

• x₁x₂

• x₁²x₂

• x₁x₂²

Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact. The effective power of the combination is

• 9 D

• 2 D

• 3 D

• 7 D

A convex lens of focal length 30 cm produces 5 times magnified real image of an object. What is the object distance?

• 36 cm

• 25 cm

• 30 cm

• 150 cm

If the focal length of the eye-piece of a telescope is doubled, its magnifying power (m) will be

• 2 m

• 3 m

• $\frac{\mathrm{m}}{2}$

• 4 m