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An object is placed at a distance of 20cm before a concave mirror. a real image is obtained at a distance of 40cm from the mirror. calculate focal length

and magnification.



V = -40 cm
u = - 20 cm
 by mirror formula we have 1/v + 1/u = 1/f
1/f = 1/-40 + 1/-20
1/f = (-1 - 2)/ 40
1/f = -3/40
f = -40/3
f = -13.3334 cm

m = - v/u
m = -(-40)/-20
m = - 40/20 = -2

Therefore, Focal lenght = -13.3334 cm and Magnification = -2
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i am meena studying in class 10th
this is my siso account
i am also studying in class 10.....!
ankit, u can use the equation editor present in the answering editor. it gives better looking answers. try clicking on Pi button when u are answering with calculations.
Thanks kvnmurthy, You are wright. I should use the editor.....!

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See diagram for visualization of the image formation.

\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\\\\u=-20cm, cartesian\ sign\ convention\\v=-40cm\\\\\frac{1}{f}=\frac{1}{-20}+\frac{1}{-40}=\frac{2+1}{-40}=\frac{-3}{40}\\\\f=focal\ length=-\frac{40}{3}=-13.33cm\\\\Magnification=-\frac{v}{u}=-\frac{40}{20}=-2\\
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hope that gives a clear view of the answer
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