Page 11 - 10-phy-12 Geometrical Optics
P. 11
Materials Semi circular glass slab, ray box / laser light, power supply (12V), single-slit slide, ruler,
Required pencil, protractor, paper sheet, drawing board and thumb pins.
Procedure 1. Fix a paper sheet on a drawing board with the help of thumb pins.
! CAUTIONS 2. Draw a straight line across the paper.
Ÿ Lasers are not toys. Do 3. Place the semi-circular glass slab such that its straight edge AB coincides
not look into the laser or with this line and mark the boundary of the circular side of the slab.
point the laser towards Rotate the slab to the other side of the straight line and mark the circular
someone's eyes. Turn boundary to complete the circle.
off the laser when you
are not using the laser 4. Remove the slab and draw a right bisector PQ of the line AB to locate the
light. centre O of the slab.
Ÿ The semi-circular slab 5. By using a single slit slide, adjust the ray box to get a single ray.
should be scratchless.
6. Fix the laser light ray in such a way that the ray of light exactly coincided
Ÿ Laser / Ray box should with the line PQ.
be placed closed to the
semi-circular side of 7. Again place the slab in the circle drawn in such a way that its straight edge
the slab. coincides with line AB and the circular edge faces towards the ray of
light. In this position the ray of light is incident normally to the edge AB at
point O and it passes through the slab undeviated.
8. Now slowly rotate the slab keeping it all the
time within the circle and observe the refracted
ray.
Why should the ray of light be
9. Gradually increase the angle of incidence by perpendicular to the semi
rotating the semi-circular slab and continue
circular edge?
observing the refracted ray till it just appears as
reflected ray on the circular side of the slab.
10. This value of incident angle is the critical angle C.
11. Remove the glass slab and measure the angle of incidence which is the
critical angle. Record this value in the table.
12. Repeat the experiment four more times and find the mean value of critical
angle.
This experiment can also be performed by using a Fig. 12.3.5
triangular glass prism instead of semi-circular glass slab. A
circle can be drawn that passes through its vertices. Then the
prism can easily be rotated within the circle with fixed centre
at O (Fig. 12.3.5).
13
Required pencil, protractor, paper sheet, drawing board and thumb pins.
Procedure 1. Fix a paper sheet on a drawing board with the help of thumb pins.
! CAUTIONS 2. Draw a straight line across the paper.
Ÿ Lasers are not toys. Do 3. Place the semi-circular glass slab such that its straight edge AB coincides
not look into the laser or with this line and mark the boundary of the circular side of the slab.
point the laser towards Rotate the slab to the other side of the straight line and mark the circular
someone's eyes. Turn boundary to complete the circle.
off the laser when you
are not using the laser 4. Remove the slab and draw a right bisector PQ of the line AB to locate the
light. centre O of the slab.
Ÿ The semi-circular slab 5. By using a single slit slide, adjust the ray box to get a single ray.
should be scratchless.
6. Fix the laser light ray in such a way that the ray of light exactly coincided
Ÿ Laser / Ray box should with the line PQ.
be placed closed to the
semi-circular side of 7. Again place the slab in the circle drawn in such a way that its straight edge
the slab. coincides with line AB and the circular edge faces towards the ray of
light. In this position the ray of light is incident normally to the edge AB at
point O and it passes through the slab undeviated.
8. Now slowly rotate the slab keeping it all the
time within the circle and observe the refracted
ray.
Why should the ray of light be
9. Gradually increase the angle of incidence by perpendicular to the semi
rotating the semi-circular slab and continue
circular edge?
observing the refracted ray till it just appears as
reflected ray on the circular side of the slab.
10. This value of incident angle is the critical angle C.
11. Remove the glass slab and measure the angle of incidence which is the
critical angle. Record this value in the table.
12. Repeat the experiment four more times and find the mean value of critical
angle.
This experiment can also be performed by using a Fig. 12.3.5
triangular glass prism instead of semi-circular glass slab. A
circle can be drawn that passes through its vertices. Then the
prism can easily be rotated within the circle with fixed centre
at O (Fig. 12.3.5).
13
