Science (086) — AI-generated practice question

(i) Calculation of Refractive Index:

$$n = \frac{\text{Speed of light in air}}{\text{Speed of light in glass}} = \frac{c}{v} = \frac{3 \times 10^8}{2.0 \times 10^8} = \mathbf{1.5}$$

(ii) Optically denser or rarer than crown glass?

The refractive index of this glass sample = 1.5, while crown glass has refractive index = 1.52.
Since 1.5 < 1.52, this glass sample is optically rarer than crown glass.
The medium with the larger refractive index is optically denser; since crown glass has a higher refractive index, it is the denser medium.

(iii) In which glass does the refracted ray make a smaller angle with the normal?

The refracted ray makes a smaller angle with the normal in crown glass (n = 1.52).
When light passes from air (rarer) into glass (denser), it bends towards the normal. A higher refractive index means greater bending towards the normal, i.e., a smaller angle of refraction. Since crown glass has a higher refractive index (1.52 > 1.5), it bends light more, giving a smaller angle with the normal.

Source: Chapter 9, Section 9.3.2 — The Refractive Index

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• Part (i): Directly apply formula $n = c/v$. Show substitution and result clearly — 1 mark for formula, 1 for correct answer.
• Part (ii): The key rule is: higher refractive index = optically denser. Since 1.5 < 1.52, this sample is rarer. State this rule explicitly — examiners award marks for the justification.
• Part (iii): At the same angle of incidence, the denser medium bends light more towards the normal → smaller angle of refraction. Crown glass is denser, so the angle is smaller there. Always link the conclusion to the concept of bending towards the normal.