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What is The focal length of the mirror used in head lamp: and explain in detail?
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)