To study refraction of light in rectangular glass slab

As performed in the real lab:


A drawing board, rectangular glass slab, office pins, sheet of white paper, a protractor and sharply pointed pencil.


  1. Fix a sheet of white paper on a drawing board with drawing pins. Place the given glass slab nearly in the middle of the sheet.
  2. Mark the boundary of the glass slab with a sharp pencil and label it as PQRS after removing the slab from its position.
  3. On the line PQ mark a point E and draw a normal N1EN2 at it. Draw a line AE making angle AEN1 with the normal.The angle should neither too small nor too large (say about 40 degree).
  4. Now place the glass slab again on its boundary PQRS and fix two pins A and B vertically about 10 cm apart on the line AE (say points A and B).
  5. Look through the glass slab along the plane of the paper from the side SR and move your head until the images of the two pins A and B are seen clearly. Closing your one eye ,adjust the position of your head in such a way that the images of the pins A and B lie in the same straight line.
  6. Fix two other pins C and D vertically in such a way that the images of the pins A and B and pins C and D, all these four, lie in the same straight line. Ensure that the feet of the pins ( not their heads ) lie in the same straight line.
  7. Remove the slab and also the pins from the board and encircle the pin-pricks on the paper,with a sharp pencil.
  8. Join the points D and C and produce the line DC towards the slab so that it meets the boundary line RS at the point F. Join the points e and F. Thus for the incident ray represented by line AE, the refracted ray and the emergant ray are represented by EF and FD respectively.
  9. On the line RS draw a normal N1'FN2'  at point F. Now, with a protractor, measure angle AEN1, angle FEN2 and angle DFN2' labelled as angle i, angle r and angle e respectively. 
  10. Now place the glass slab at some other position on the sheet of paper fixed on the board and repeat all the above steps again taking another angle of incidence.
  11. Measure the angle of incidence i.e angle of refraction, angle of emergence, again.
  12. Make a record of your observations in the observation table as shown below.


 Observation Table :



As performed in the simulator:

  1. Click on Show values checkbox to display the refractive indices of air and glassangle of incidence and angle of refraction.
  2. Move the Observer to get an approximate emergent ray.
  3. Note down the angle of incidenceangle of refraction and angle of emergence in the Observation Table.
  4. To view the actual emergent ray click on Emergent Ray checkbox.
  5. Use the slider to change the angle of incidence, and repeat the above steps.