Name Jonathan Tam Class: 13A
Yew Chung International School Physics
Aim: Find the refractive index of a plastic block
Method:
I will use two methods to find the refractive index of plastic. The first one is to use the critical angle, and the other one is to use Snell’s Law.
Critical Angle method:
- Set up the apparatus as shown. Put a piece of white paper under the apparatus. Turn off lights from the surroundings.
- Put a black slid into the light box so that only a thin ray will be shone.
- Turn on the light box. Adjust the angle of incidence so that there are no refracted rays. Once the refracted ray disappears, the angle of incidence is the critical angle. You should start seeing a reflected ray coming out of the plastic block as shown above.
- Plot points on the paper to show the light rays. Connect the points to form lines.
- Draw normal on the paper between the incident ray and reflected ray as shown. Measure angle i (angle of incidence, critical angle)
- Repeat step 3 to 5 at least 3 times to get sufficient results.