Question

An object of size 7cm is placed at 20cm in front of concave mirror of focal length 18cm find the nature and size of image.

Answer 1

We know that, for a concave mirror the focal length will be negative.

Therefore, given: u = -27cm     f = -18cm    h(object size) = 7cm

( Note that the distance at which you will obtain sharp image will be your "v" i.e.  the object distance for that  image formation which is required in the question)

hence,

1/v + 1/u = 1/f                                       (mirror formula)

1/v + (1/(-27)) = 1/(-18)

1/v  =   1/27 + 1/-18                              ( LCM of 18 and 27 is 54)

1/v  =  1/(-54)

v     =  -54cm

image distance = -54cm

hence, image is formed on the same side.

now we know,

h'/h = -v/u                                             (h' denotes object height)

h'/7 = -(-54)/-(27)

h'    =  7 * (-2)

h'    =  -14cm

hence, image is inverted (since h' is negative) and it is on the same side of that of the object (since v is negative).

HOPE IT HELPS .

Answer 2

Answer:

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