The graps shows the variation of magnification `m` produced by as convex lens with the image distance `v`. The focal length of the lens is

Options

A. `(b)/(c)`
B. `(c)/(b)`
C. `a`
D. `a,(b)/(c)`

Answer

D

Explanation

For lens `(1)/(v)-(1)/(u)=(1)/(f)implies(1)/(v)-(1)/(-u)=(1)/(f)`
`(v)/(v)+(v)/(u)=(v)/(f)implies(v)/(u)=(v)/(f)-1`
`m=(v)/(f)-1impliesu=(1)/(f)x-1`
Comparing with `y=Mx+C`
Slope `M=(1)/(f)=(b)/(c)impliesf=(c)/(b)`