Question

when the focal length, position of image and position of object are (+) and( - )​

Answer 1

HELLO DEAR FRIEND

WHEN FOCAL LENGTH IS NEGATIVE

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THEN THE OBJECT IS VIRTUAL AND ERECT .

SMALLER THAN THE OBJECT.

IN THIS SITUATION IMAGE FORMED WILL ALWAYS AT THE SAME SIDE OF THE OBJECT.

IT HAPPENS IN CONCAVE LENS

AND CONVEX MIRROR

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WHEN THE FOCAL LENGTH IS POSITIVE

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THE IMAGE FORMED WILL BE REAL AND ERECTED.

IN THIS SITUATION IMAGE FORMED WILL BE BEHIND THE LENS EXCEPT WHEN

THE OBJECT IS BETWEEN FOCUS AND LENS.

IT HAPPENS IN CONVEX LENS AND

CONCAVE MIRROR.

HOPE IT HELPS YOU DEAR FRIEND THANKS

Answer 2

Answer:

Object position (u) = - 20 cm (-ve sign due to position of object opposite to direction of incident ray)

Focal length (f) = -20 cm (focal length of concave mirror is always negative)

Mirror formula

1/f = 1/u + 1/v

-1/20 = -1/20 + 1/v

1/v = -1/20 + 1/20

1/v = 0

v = infinite ( not defined)