3B Scientific Light Box - Manual (Page 4)

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2. The incident ray, normal ray and reflected ray, all lie in the same plane.
Besides these laws, there are other important features of reflection that we come across every day, i.e.,
lateral inversion, shaving mirrors, rear-view mirrors etc.
Reflection from a Plane Mirror: Adjust the collimating lens so that the resultant beam of light is
parallel. Allow a single ray to pass out of the light-box (use a slit plate). Mark its position on the paper.
Place the plane mirror in its path, at an angle. Mark the position of the mirror and that of the reflected
ray. Remove the mirror and draw a normal to the outline of the mirror at the point where the incident
and reflected ray meet the outline. Measure the angles between the normal and incident rays and
normal and reflected rays to obtain the angles of incidence and reflection. Check that the FIRST LAW
OF REFLECTION is verified.
Next, replace the slit plate by the multiple slit plate with three or four slits. As above, place the mirror
in the path of the rays and measure the various angles of incidence and reflection.
Next, place a concave (or convex lens) in the path of the rays to obtain diverging (or converging) rays
falling on the mirror. After plotting their paths, measure the various angles, and answer the following
questions:
• Do these observations match with what you expected?
• What happens to the parallel, converging and diverging rays after they are reflected?
Reflected Images in a Plane Mirror: Set up the apparatus so that multiple converging rays fall on the
mirror. On looking into the mirror, you will see that the incident rays and the images of the reflected
rays appear to form the complete straight line paths of the incident rays (and vice-versa). This can be
verified by lifting the mirror and observing the real converging rays.
• Are the image of the reflected focus and the real focus (in the absence of the mirror) the same
point?
• Join the real and reflected foci by a straight line. What angle does it make with the mirror?
• Why is the image of the reflected rays fainter than the actual rays observed by removing the
mirror?
Lateral Inversion: When you look at an object and then at its image in a mirror, the two are observed
not to be identical.
• What is different about them?
The above phenomenon is called lateral inversion.
Remove all slit-plates from the light-box and adjust the collimating lens for a parallel beam of light.
Stand a pencil in the left (or right) corner of the opening and then look at the image in the mirror.
Where does the pencil stand?
• From the above experiment can you explain why lateral inversion occurs?
Place a multiple slit-plate in the opening so that four parallel rays fall on the mirror. Hold the red filter
in front of two slits and the violet filter in front of the other two so that the two inner rays are stopped
by the filter frames and the outer rays are of different colors. Observe the image.
• Are the rays from the left side of the light-box and the image on the left side the same color?
Look at yourself in a plane mirror. Do you observe any vertical inversion?
• Why does vertical inversion not occur?
If you observe the image of the word MAXAYAXAM in the mirror, what do you expect to see?