An automated sorting machine checks the surface finish of opaque plastic pieces.
A narrow beam containing parallel rays strikes each piece. Each piece is tested in the same position and with the same overall orientation. Four light sensors, P, Q, R and S, are placed at equal distances from the point where the beam strikes the piece, but in different directions.
The table shows the sensor readings for two pieces.
| piece | sensor P reading | sensor Q reading | sensor R reading | sensor S reading |
|---|---|---|---|---|
| X | 24 | 28 | 23 | 25 |
| Y | 3 | 92 | 2 | 3 |
All readings are in arbitrary units.
Explain which piece has the smoother surface. Use the results in the table.
Explain why piece X produces substantial readings at all four sensors even though every reflected ray obeys the law of reflection.
Piece X is polished to make its surface smooth without changing its overall orientation.
Explain how the pattern of sensor readings for X would be expected to change.
93 exam-style questions on Edexcel GCSE Physics 5.1 Reflection, refraction and lenses, covering 5.1.1 Reflection, refraction and total internal reflection, 5.1.2 Specular and diffuse reflection, 5.1.3 Colour of light: absorption and filters, 5.1.4 Lenses: power, focal length and shape, 5.1.5 Ray diagrams for converging and diverging lenses, and 5.1.6 Real and virtual images. Each one has a worked solution and a mark scheme showing where the marks go.