Question

an object is placed in front of a concave mirror of focal length 20 cm the image formed is 3 times the sizee of the object calculate 2 possible distancesof the object from the mirror

Answer 1

Answer:

$It \: is \: given \: that, \: </p><p></p><p>Focal \: length</p><p></p><p>f=−20 \: cm \: </p><p></p><p>hi=3ho</p><p></p><p></p><p>$

The image is three times the size of the object. So there are two cases.

Case 1. For real image

$m=−uv=−3 \\ </p><p></p><p>v=3u</p><p></p><p>$

$Using \: mirror’s \: formula</p><p></p><p>f1=v1+u1 \</p><p></p><p>−201=3u1+u1</p><p></p><p>u=3−80cm</p><p></p><p>$

Case 2. For virtual image

$m=u−v=+3 \\ </p><p></p><p>v=−3u</p><p></p><p>$

Again using mirror’s formula

$</p><p>−201=−3u1+u1 \\ </p><p></p><p>u=3−40cm</p><p></p><p>$

The possible values of u are

$3−80cm \: and \: 3−40cm.$

Answer 2

Answer:

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