Light – Glass block - Experiment 1

EXPERIMENT NO. 1

The aim of this experiment is to determine the refractive index of the glass block provided.
Proceed as follows;
Place a white sheet paper on the drawing board. On top of this white paper place the glass block with one of its largest faces top most. Mark its outline ABCD on the paper with a sharp pencil. Remove the block and draw a line that cuts AB normally at E and G (call it FEG)
 Draw a line HE making an angle of incidence i° = 200 with EGF at O. Put the glass block in its original
position and stick the first pin P1 and second pin P2 along the line HE of angle = 200. The third and the fourth pins P3 and P4 respectively, should be stuck on the opposite side of the block such that they appear in a straight line with P1 and P2 when viewed through the side AB of the glass block. Remove the glass block and trace the straight path taken by the ray IP3P4. Join E and I using a rule
Measure the angle of refraction r° and the calculate the value of the values sin i° and sin r°

(a)  Repeat the procedures above for an angle of incidence i° = 400, 500, 600 and 800 and in all cases calculate the value of respective sin i° and sin r°
(b)  Tabulate your results as shown below

A table of results
Angle of incidence i°
Angle of refraction r°
sin i°
sin r°


























(c)  (i) Draw the graph of sin i° (y-axis) against sin r° (x-axis)
(ii) Find the slope of the graph
(iii) What is the physical meaning of the slope obtained in (c) (ii) above
(d)  State all possible sources of errors in this experiment and state the precautionary measures that are to be taken in order to reduce the effect of those errors



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