Ray Optics and Optical Instruments

Q1.A ray of light passes from water (n = 4/3) to glass (n = 3/2). If the angle of incidence is 30°, what is the angle of refraction?

• Asin⁻¹(8/9) ≈ 62.7°
• Bsin⁻¹(8/9) is impossible
• Csin⁻¹(8/18) = sin⁻¹(4/9) ≈ 26.4°
• D30°

Q2.The magnifying power of a refracting telescope in normal adjustment is:

• Am = fe/fo
• Bm = fo/fe
• Cm = fo + fe
• Dm = fo × fe

Q3.A convex lens of glass (n = 1.5) has both surfaces with equal radii of curvature R. Using the lens maker's formula (lens in air), the focal length f is:

• Af = R
• Bf = R/2
• Cf = 2R
• Df = R/4

Q4.The refractive index of water is 1.33. A needle lies at the bottom of a water tank 12.5 cm deep. A microscope measures apparent depth as 9.4 cm. What is the measured refractive index and how far must the microscope move if water is replaced by a liquid of n = 1.63?

• An_water ≈ 1.33; move up by 1.73 cm
• Bn_water ≈ 1.33; move up by 3.1 cm
• Cn_water ≈ 1.33; move down by 1.73 cm
• Dn_water ≈ 1.33; move up by 4.83 cm

Q5.A light pipe (optical fibre) has a core with refractive index 1.68 and cladding with refractive index 1.44. The critical angle at the core-cladding interface is approximately:

• Asin⁻¹(1.44/1.68) ≈ 58.97°
• Bsin⁻¹(1.68/1.44) — impossible
• Csin⁻¹(1.44) — impossible
• D45°