1. To verify Snells Law and find the refractive index of glass

2. Method Place a glass block on the paper and mark its outline.
Shine a ray of light from a lamp through the block and mark the incident and emergent rays.
Remove the glass block. Join where the ray enters and leaves the block.
Draw the normal and measure the angle of refraction r and the angle of incidence.
Repeat for different values of i.
Plot a graph of sin i against sin r.

3. Results i r
Sin i
Sin r n
The refractive index of glass is equal to the average value of sin i divided by sin r or the slope of the graph.

4. Precautions
Avoid the small angles as they have a greater percentage error.
Use a narrow beam of light as its position can be marked more accurately.