(Guiding a Laser Beam)
A laser beam travels in air along a straight line that lies completely on a drawing sheet placed on a horizontal laboratory table. The beam strikes a plane mirror at point O. A sensor S is marked at another position on the same sheet. The mirror can be rotated only about a vertical axis passing through O.
(a) State the geometrical condition that the normal at O must satisfy so that the reflected beam reaches the sensor S.
(b) On the sheet, construct the path of the incident and the required reflected rays and show the position of the correct normal.
(c) If the mirror is accidentally tilted forward so that its top edge moves 5° towards the student, predict qualitatively whether the beam can still reach S without changing the direction of the incident ray. Give reason for your answer.