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.
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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