Question

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

Answer 1

Answer:

Explanation:

object distance, u = -4 cm

magnification, m= 4

we know, m = -v/u ⇒ v = -mu ⇒ v = -(4)(-4) = 16 cm

so image distance= 16 cm

now, by mirror formula ,

   1/v + 1/u = 1/f

⇒ 1/16 + 1/-4 = 1/f

⇒ (1-4)/16 = 1/f

⇒ 1/f = -3/16

∴ focal length = -5.33 cm

only a concave mirror can form magnified images.

since the image is formed behind the mirror, it is virtual and erect

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