1.

Aperture of lens of a camera is f and its exposure time is (1)/(60) s. If aperture becomes 1.4 f, then what will be the exposure time ?

Answer»

`(1)/(42)` s
`(1)/(56)` s
`(1)/(72)` s
`(1)/(31)` s

Solution :Exposure time `t prop F^2`
`therefore ((t_2)/(t_1))=((f_2)/(f_1))^2`
`therefore t_2=t_1xx((f_2)/(f_1))^2`
`=(1)/(60)xx((1.4f)/(f))^2`
`=((1.4)^2)/(60)=0.03266`
`therefore t_2=(1)/(31)` s


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