When an object is kept in front of a concave mirror of a focal length of 10 cm, a real image is formed at a distance of 20 cm in front of the mirror. Here, the object distance is .............
− 20 cm
The correct answer is option 4 i.e. − 20 cm.
To find the object distance (u) for a concave mirror, we use the mirror formula:
1/f=1/v + 1/u
Given:
-
Focal length (f) = –10 cm (negative for concave mirror)
-
Image distance (v) = –20 cm (real image formed in front of the mirror)
Now, substitute values:
1/−10 =−1/−20 + 1/u
u/1=−1/−10 −1/−20 = −1/10 + 1/20 = −1/20
u = −20 cm
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