A student investigates the reflection of light by a plane mirror. They rotate the mirror by an angle θm\theta_{\text{m}}θm from its initial horizontal position and measure the angle of deviation δ\deltaδ of the reflected ray from the normal line.
The results obtained are shown in the table below:
| Trial | Angle of rotation of the mirror θm/∘\theta_{\text{m}} / ^\circθm/∘ | Angle of deviation δ/∘\delta / ^\circδ/∘ |
|---|---|---|
| 1 | 15.0 | 29.5 |
| 2 | 25.0 | 51.5 |
| 3 | 35.0 | 69.0 |
(i) State a typical minimum recommended distance between two optical pins, P1P_1P1 and P2P_2P2, used to define a ray.
(ii) Explain why placing these pins too close together reduces the accuracy of the experiment.
Another student suggests that the angle of deviation is related to the rotation angle of the mirror by the formula δ=2θm\delta = 2\theta_{\text{m}}δ=2θm. State whether the results in the table support this suggestion. Justify your answer by comparing the values.
Suggest two practical precautions, other than pin separation, that should be taken to ensure that the ray-tracing results are as accurate as possible.
216 exam-style questions on CIE IGCSE Physics 3.2 Light, covering 3.2.1a Reflection of light, 3.2.1b Images in a plane mirror, 3.2.2 Refraction of light, 3.2.2a Refraction of light, 3.2.2b Total internal reflection, 3.2.2c Refractive index and critical angle, 3.2.2d Optical fibres, 3.2.3a Converging and diverging lenses, 3.2.3b Ray diagrams and the nature of images, 3.2.3c Virtual images and the magnifying glass, 3.2.3d Correcting long-sightedness and short-sightedness, and 3.2.4 Dispersion of light. Each one has a worked solution and a mark scheme showing where the marks go.