The distance between the focus of a concave mirror and an object is doubled and along with that the distance between the focus of the same mirror and the image formed is also doubled ; so the focal length will be
2 times than the previous
Same
4 times than the previous
8 times than the previous
Let us assume that the distance in between the focus of the concave mirror and the object is “x”And the distance in between the focus of the mirror and the image formed is “y”And the focal length is “f”
From Newton’s formula of mirror we can define
Now “x” has became “2x” and “y” has became “2y”
So the updated focal length will be
From here you can see that the focal length becomes double
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