Question

how far should an object be from the pole of the concave mirror of focal length 20cm to form a real image whose size is one-fifth the size of the object.

Answer 1

Focal length of concave mirror,f = – 20cm ( – ive for concave mirror)
Size of image ,I = 1/5 of size of object = 1/5 * O,
where,I = size of image
O = size of object
object distance, u = ?
image distance = v
Solution ---
Magnification,m is given as,
m = I/O = – v/u ( ratio of size of image to size of object which is equal to ratio of image distance to object distance)
1/5 = – v/u
or, v = – u/5
now applying the mirror formula,
1/f = 1/u + 1/v
– 1/20 = 1/u – 5/u
1/20 = 1/u + 5/u as image is real so v will be negative so on putting its value it becomes positive
or, u= – 120cm

Answer 2

Answer:

Explanation:

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