Science (086) — AI-generated practice question

(i) Angle of Refraction:

Using Snell's law: $n = \dfrac{\sin i}{\sin r}$

$$1.5 = \frac{\sin 45°}{\sin r} = \frac{0.707}{\sin r}$$

$$\sin r = \frac{0.707}{1.5} = 0.471$$

$$r = \sin^{-1}(0.471) \approx 28.1°$$

(ii) At the second parallel surface, the ray goes from glass (denser) to air (rarer), so it bends away from the normal. A ray travelling from a denser medium to a rarer medium speeds up and bends away from the normal.

(iii) Speed of light inside glass is less than in air. Since $n = \dfrac{c}{v}$, and $n = 1.5 > 1$, the speed in glass $v = \dfrac{3 \times 10^8}{1.5} = 2 \times 10^8$ m s$^{-1}$.

Source: Chapter 9, Sections 9.3.1 and 9.3.2

---

• Part (i): Apply Snell's law directly. Show the substitution step — examiners award marks for working, not just the final answer.
• Part (ii): The key reason is denser→rarer = bends away from normal. This is a one-line conceptual answer; state the direction AND the reason.
• Part (iii): Use $n = c/v$ to both explain and calculate. The answer $2 \times 10^8$ m s$^{-1}$ shows the speed is reduced to ⅔ of its value in air.