Refractive index of glass (pin method)

A/L Physics · G.C.E. Advanced Level · Grades 12–13

Aim

To find the refractive index of a glass block by the pin method.

Apparatus

• A rectangular glass block
• 4 pins and paper
• Protractor

Method

1. Place the block on paper, draw its outline and a normal.
2. Stick two pins along the incident ray.
3. View from the other side and place two more pins in line.
4. Measure i and r; plot sin i against sin r: gradient = n.

Conclusion

sin i ÷ sin r is constant (Snell’s law) and equals the refractive index n ≈ 1.5 for glass.