Laws of Refraction and Snell's Law - UNSOLVED PRACTICE SET

Q7. State the two laws of refraction of light. What is the second law also known as?

Q8. What causes refraction? If light enters a denser medium, does it speed up or slow down? What happens to its direction?

Q9. State Snell's Law in both word form and as a mathematical equation. What does the constant in Snell's Law represent?

Q10. A ray of light goes from air (n = 1) into glass at an angle of incidence of 60°. The refracted angle is 35°. Calculate the refractive index of the glass. (sin 60° = 0.866, sin 35° = 0.574)

Q11. Explain with a diagram why a pencil partially dipped in water appears bent at the surface. Name the phenomenon and state which law governs it.

Q12. Does refraction change the frequency of light? Does it change the wavelength? Does it change the speed? Explain each answer.

Q13. State and explain the laws of refraction in detail. Your answer must cover:
(a) the first law (coplanarity of incident ray, refracted ray, and normal),
(b) Snell's Law as the second law — state it and explain what n₁ sin θ₁ = n₂ sin θ₂ means physically,
(c) what happens to the direction of light when going from air to glass vs glass to air,
(d) why does refraction occur at all (connect to change in speed), and
(e) give two real-life Indian examples where refraction can be observed.

Q14. A fisherman standing at the edge of a pond in Kerala is trying to spear a fish he sees underwater.
(a) Why does the fish appear to be at a different position from where it actually is?
(b) Should the fisherman aim directly at the image of the fish, above it, or below it? Explain using Snell's Law and the direction of bending.
(c) Draw (or describe) the ray diagram showing the apparent and real positions of the fish.
(d) What is the general rule: objects underwater always appear shallower or deeper than they are?
(e) If light travels from water (n = 1.33) into air (n = 1), and the angle in water is 30°, find the angle in air. (sin 30° = 0.5)

Q15. Explain Snell's Law using a mathematical derivation or physical reasoning.
(a) Write Snell's Law in terms of velocities: n₁ sin θ₁ = n₂ sin θ₂, where n = c/v.
(b) Show that sin i / sin r = v₁/v₂ = n₂/n₁.
(c) If n₁ < n₂ (denser medium), show mathematically that θ₂ < θ₁ (ray bends toward normal).
(d) Verify using an example: light going from air (n = 1) to diamond (n = 2.42) at i = 30°. Find r. (sin 30° = 0.5) (e) Why does diamond sparkle so brilliantly? Connect to its high refractive index and Snell's Law.

Q16. A ray of light passes from air into water at an angle of incidence of 50°. The refractive index of water = 1.33.
(a) Using Snell's Law, find the angle of refraction.
(b) Does the ray bend toward or away from the normal? Why?
(c) If the same ray now exits from water back into air, what is the angle of refraction in air? (sin 50° ≈ 0.766)

Q17. Light travels from medium A (n = 1.5) to medium B (n = 1.2). The angle of incidence in A is 40°.
(a) Write Snell's Law for this situation.
(b) Calculate the angle of refraction in B.
(c) Does the ray bend toward or away from the normal as it enters B?
(d) Which medium is optically denser? (sin 40° ≈ 0.643)

Q18. A ray of light hits the boundary between glass (n = 1.5) and air (n = 1.0) at 25° to the normal.
(a) Calculate the angle of refraction in air.
(b) As the angle of incidence in glass is increased, at what critical angle will the refracted ray travel along the boundary (r = 90°)?
Find the critical angle C using: sin C = n₂/n₁.
(c) What happens for angles of incidence greater than C? Name this phenomenon. (sin 25° ≈ 0.423)