Verification of snell's law of refraction

Apparatus

Glass block, lamp-box, 0-3600 protractor, (photocopied from page 56 of Physics A Teacher's Handbook)

Procedure

• Place a glass block on the 0-360 protractor in the position shown on the diagram and mark its outline.

• Shine a ray of light from a lamp-box at a specified angle to the near side of the block and note the angle of incidence.

• Observe the ray of light leaving the glass block and similarly mark the exact point B where it leaves the glass block.

• Remove the glass block. Join BA and extend to C.

• Note the angle of refraction r.

• Repeat for different values of i.

• Draw up a table as shown.

• Plot a graph of sin i against sin r.

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Verification of snell's law of refraction

Results

$i/°$	$r/°$	$\sin i$	$\sin r$	$\frac{\sin i}{\sin r}$

Average value of $\frac{\sin i}{\sin r} =$

A straight line through the origin verifies Snell's law of refraction i.e. $\sin i ∝ \sin r$.

The slope of the line gives a value for the refractive index of glass.

The refractive index of glass is equal to the average value of $\frac{\sin i}{\sin r}$.