Intensity and refractionEdexcel International A Level Physics: Mind map

Exam questions on Intensity and refraction

1. A small lamp radiates light uniformly in all directions with a total power of 40 W. Treat the lamp as a point source and assume that no light is absorbed or scattered by the air.
   Calculate the distance from the lamp at which the intensity is 0.20 W m⁻².2 marks
2. A ray of light in air strikes the flat surface of a glass block at an angle of incidence of 40°. The refractive index of the glass is 1.50 and the speed of light in air is 3.00 × 10⁸ m s⁻¹.
   The ray leaves the glass and enters water of refractive index 1.33 at the interface at an angle of incidence of 30°. Calculate the angle of refraction in the water.2 marks
3. In Core Practical work a student measures the refractive index of a rectangular block of transparent plastic. She uses a ray box to send a narrow ray into the block at different angles of incidence i and measures the angle of refraction r each time. She plots sin i on the y-axis against sin r on the x-axis and obtains a straight line through the origin with gradient 1.49. Take the speed of light in air as 3.00 × 10⁸ m s⁻¹.
   Describe how she should carry out the experiment to obtain a suitable set of measurements of i and r, and how she should use them to find the refractive index.3 marks