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A ray diagram shows how light travels, including what happens when it reaches a surface.

In a ray diagram, you draw each ray as:

• a straight line;
• with an arrowhead pointing in the direction that the light travels.

Remember to use a ruler and a sharp pencil.

Investigating the law of reflection

• On a sheet of white paper draw a pencil line – label this AB.
• Using a protractor, draw a normal at C, roughly the middle of AB.
• Draw a line at 20^o to the normal.
• Position a plane mirror carefully along AB.
• Direct a ray of light from a ray box along the 20^o line – this is the incident ray. Record the angle of incidence i in a suitable table.
• Use 2 pencil Xs to mark the position of the reflected ray.
• Take away the mirror and join these Xs back to C. This is the reflected ray. Put an arrow on it to show its direction.
• Measure the angle between the normal and the reflected ray with the protractor and record the angle of reflection r in the table.
• Repeat the experiment for a series of incident rays.

Results

Conclusion

When light is reflected by a plane mirror:

the angle of incidence = the angle of reflection.

This is known as the law of reflection.