A student is investigating the refraction of light passing through a glass block WXYZWXYZWXYZ. A normal line is drawn at the centre of side WXWXWX. The line is extended to cross the opposite side ZYZYZY. The point where the normal crosses WX WX\,WX is labeled AAA, and the point where it crosses ZY ZY\,ZY is labeled BBB.
An incident ray is drawn to the left of the normal on the side WXWXWX, meeting it at point A A\,A with an angle of incidence θ1\theta_1θ1. Two pins P1 P_1\,P1 and P2 P_2\,P2 are placed on this incident ray.
By looking through the side ZYZYZY, the student aligns two more pins P3 P_3\,P3 and P4 P_4\,P4 with the images of P1 P_1\,P1 and P2P_2P2. The line connecting P3 P_3\,P3 and P4 P_4\,P4 is extended backwards until it intersects the extended normal line at point CCC.
The student measures:
The experiment is carried out for two different angles of incidence, θ1=35∘\theta_1 = 35^\circθ1=35∘ and θ1=55∘\theta_1 = 55^\circθ1=55∘. The results are shown in the table:
| Angle of incidence θ1\theta_1θ1 | Measured angle β\betaβ | Measured distance ddd |
|---|---|---|
| 35∘35^\circ35∘ | 37∘37^\circ37∘ | 14 mm |
| 55∘55^\circ55∘ | 58∘58^\circ58∘ | 26 mm |
State a suitable recommended minimum distance between the pins P1 P_1\,P1 and P2 P_2\,P2 to ensure accuracy when drawing the ray paths.
A student suggests that the measured angle β \beta\,β should theoretically be equal to the angle of incidence θ1\theta_1θ1. State whether the experimental results support this suggestion. Justify your statement with reference to the values in the table.
State two physical precautions that should be taken during this experiment to achieve reliable results.
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.