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If x and y denote the distance of the ob...

If x and y denote the distance of the object and image from the focus of a concave mirror . The line `y=4x` cuts the graph at a point whose abscissa is `20` cm. The focal length of the mirror is

A

`20` cm

B

40cm

C

30 cm

D

can't be determined

Text Solution

Verified by Experts

The correct Answer is:
B
For x = 20 cm , y= `4xx20 = 80` cm
From Newton's formula xy = `f^(2) implies (2)(80) = f^(2) implies f = 40` cm
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