How can we change a camera from F/4 to F/5.6?

Options

A. Increase the aperture to 2 time keeping the focal distance constant.
B. Increase the aperture to `sqrt2` time keeping the focal distance constant.
C. Increase the aperture to `(1)/(2)` time keeping the focal distance constant.
D. Increase the aperture to `(1)/(sqrt2)` time keeping the focal distance constant

Answer

D

Explanation

`"F- number of camera "=(f)/("diameter of aparture")`
For F/4 camera, F number is 4, so
`4=(f)/(D_(1))`
For F/5.6 camera, F number is 5.6, so
`5.6=(f)/(D_(2))" "rArr" "(D_(2))/(D_(1))=(4)/(5.6)=(1)/(sqrt2)rArr D_(2)=(D_(1))/(sqrt2)`