An object of height 6 cm is placed perpendicular to the principal axis of a concave axis of a concave lens of focal length 5 cm. Use lens formula to determine the position, size and nature of the image if the distance of the object from the lens is 10 cm.

Options

A. `(2hepsilon_0 m u^2)/(ex^2)`
B. `(hepsilon_0 m u^2)/(ex^2)`
C. `(h epsilon_0 m u^2)/(2ex^2)`
D. `(2h epsilon_0 m u^2)/(ex)`

Answer

A

Explanation

Direction of electric field is upward and its magnitude , `E=sigma/epsilon_0`
Downward acceleration of electron , `a=(esigma)/(mepsilon_0)`
Horizontal speed is constant and hence time taken ,
`t=x/u`
Electron is starting from rest.
`S=1/2 at^2 rArr h=1/2 (e sigma)(m epsilon_0)(x/u)^2 rArr sigma=(2h epsilon_0 m u^2)/(ex^2)`