WAEC - Physics (1999 - No. 21)
A ray of light is incident on 'a plane mirror at an angle of 20o. This mirror is rotated through, twice this angle, In this new position the angle between the incident ray and the reflected ray is
20o
40o
80o
120o.
Explanation
GIVEN:
The angle of incidence i = 20º, Rotation of the mirror = 2 x 20º = 40º, Then the new angle of incidence i after rotation of mirror = 20º + 40º
But, angle of reflection r = angle of incidence i ( law of reflection)
Therefore, the angle between the incident ray and the reflected ray = i + r = 60º + 60º = 120º
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