Question

A square plate of side 4.0 cm is placed 20 cm away from a concave mirror of focal length 15 cm.

Calculate the area enclosed by the image of the plate.

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Answer 1

1/v= 1/f -1/u = 1/v = 1/15 - 1/20 = 1 /60 so,

Answer 2

Given,

A sqaure Plate of side:-$4.0cm$

Distance from the concave mirror=$20cm$

Focal length$=15cm$

Thus we have to Calculate the area enclosed by the image of the plate.

Here we have to use the Formula of Focal Length i.e

$\begin{array}{l}\frac{1}{f}=\frac{1}{u}+\frac{1}{V} \\\frac{1}{15}=\frac{1}{v}+\frac{1}{20}\end{array}$

Further Solving the above equation,

$\frac{1}{v} =\frac{1}{20} -\frac{1}{15}$

Thus we get $v=\frac{60}{1}$

Further solving the magnitude of magnification =$\frac{v}{u} =\frac{60}{20}$

$\frac{v}{u} =3$

So the area enclosed by the image of the plate will be,

$=4*4*3*3\\=144sq.cm$