Ray Optics and Optical Instruments

White light is incident normally on a glass slab. Inside the glass slab

• all colours travel with the same speed

• red light travels faster than other colours

• violet light travels faster than other colours

• yellow light travels faster than other colours

Two thin plano-convex lenses each of focal length f are placed as shown in the figure. The ratio of their effective focal lengths in the three cases is

• 3 : 2 : 1

• 1 : 2 : 3

• 1 : 2 : 1

• 1 : 1 : 1

The speed of light in media M₁ and M₂ are 1.5 x 10⁸ ms^-1 and 2 x 10⁸ ms^-1 respectively. A ray travels from medrum M₁ to the medium M₂ with an angle of incidence θ. The ray suffers total internal reflection. Then the value of the angle of incidence θ is

• $> {\sin }^{-1} \left(\frac{3}{4}\right)$

• $< {\sin }^{-1} \left(\frac{3}{4}\right)$

• $= {\sin }^{-1} \left(\frac{3}{4}\right)$

• $\le {\sin }^{-1} \left(\frac{3}{4}\right)$

A cylindrical tube of length 0.2 m and radius R with sugar solution of concentration C produce a rotation of θ in the plane of vibration of a plane polanzed light. The same sugar solution is transferred to another tube of length 0.3 m of same radius. The remaining gap is filled by distilled water. Now the optical rotation produced is

• θ

• $2 \frac{\mathrm{\theta }}{3}$

• $3 \frac{\mathrm{\theta }}{2}$

• $9 \frac{\mathrm{\theta }}{4}$

Radii of curvature of a converging lens are in the ratio 1 : 2. Its focal length is 6 cm and refractive mdex is 1.5. Then its radii of curvature are respectively

• 9 cm and 18 cm

• 6 cm and 12 cm

• 3 cm and 6 cm

• 4.5 cm and 9 cm

Pick out the wrong statement from the following

• Lateral shift increases as the angle of incidence increases

• Lateral shift increases as the value of refractive index increases

• Normal shift decreases as the value of refractive index increases

• Both normal shift and lateral shift are directly proportional to the thickness of the medium

The refraction through the prisms are as shown. Pick out the wrong statement from the following. Path of the light ray in

• a is correct if n₂ > n₁ and n₂ > n₃

• b is correct if n₁ = n₂ and n₂ > n₃

• c is correct if n₂ < n₁ and n₂ = n₃

• d is correct if n₁ > n₂ and n₂ < n₃

The distance between an object and its image produced by a converging lens is 0.72 m. The magnification is 2. What will be the magnification when the object is moved by 0.04 m towards the lens ?

• 2

• 4

• 3

• 6

An object is placed at 20 cm in front of a concave mirror produces three times magnified real image. What is the focal length of the concave mirror ?

• 15 cm

• 6.6 cm

• 10 cm

• 7.5 cm

A focal length of a lens is 10 cm. What is power of a lens in dioptre ?

• 0.1 D

• 10 D

• 15 D

• 1 D