WAEC Physics 2018 Theory — Question 19
Question 19 of 27 from the West African Examinations Council (WAEC) Physics 2018 Theory paper, with the correct answer and a full explanation.
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10.(b)(i) Explain critical angle. (ii) A ray of light passing through a rectangular transparent plastic block makes an angle of 44° as shown. (a) Determine the value of the critical angle. (b) Calculate the refractive index of the block.
Model answer
(i) The critical angle is the angle of incidence (in the denser medium) for which the angle of refraction in the less dense medium is 90°. (a) ic + 44° = 90° → ic = 46°. (b) Refractive index η = 1/sin(ic) = 1/sin46° ≈ 1.39.
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