Q. 144.5( 4 Votes )

A dentist uses a mirror in front of a decayed tooth at a distance of 4 cm from the tooth to get four times magnified image in the mirror. Use mirror formula to find the focal length and nature of the mirror used.

Answer :

Given;

Magnification (m) = 4;


Object distance (u) = -4cm;


Image distance = v;


Magnification (m) =



v = 4 × 4 = 16cm


Image distance = 16cm.


By mirror formula;







Hence the focal length is -5.33cm. Since the focal length is negative therefore the mirror is concave.


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