The focal length of the mirror used in head lamp:
Ans. is c i.e. 250 mm Head mirror is a concave mirror used to reflect light from the bull's eye lamp onto the pa being examined It has focal length of -- 25 cm (= 10 inch) The examiner sees through the hole in the centre of the mirror Diameter of central hole = 19 mm (3/4 inch)
85 mm
150 mm
250 mm
400 mm