1.

A short linear object of length l lies on the axis of a spherical mirror of focal length f, at a distance x from the mirror. Then, the length of the image (P) so obtained will be

Answer»

`(If)/((X-f))`
`(If^(2))/((x-f)^(2))`
`(If)/x`
`(I(x-f))/x`

Solution :(b) Here `u=-x,F=-f`
`:' 1/V+1/u=1/F`
or `1/v-1/x=-1/f` or `1/v=1/x-1/f=(f-x)/(XF)`
`:.v=(xf)/(f-x)`
`:. (Deltav)/(DELTAU)=(v^(2))/(u^(2))=((xf)/(f-x))^(2)xx1/(x^(2))=(f^(2))/((f-x)^(2))`
`:. Deltav=(f^(2)l)/((x-f)^(2))` [ `:' Deltau=l`]


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