A convex lens and a concave lens, each of focal length 10 cm, are kept separated by a distance of 2 cm as shown in the figure. If the light is incident from left, the combination of lenses will be :

Options

A. converging
B. diverging
C. behaving like a glass slab
D. converging or diverging depending on whether the lenes are arranged as shwon in the figure on in the reverse order.

Answer

A

Explanation

We know that the , focal leght of combination of lenses,
As `(1)/(f) = (1)/(f_(1)) + (1)/(f_(2)) - (d)/(f_(1)f_(2))`
It is given that focal length of convex lens, `f_(1) = 10 cm`
It is given that focal length of concave lens `f_(2) = - 10 cm`
distance between lenses, d = 2 cm
Then, focal lenght of the combination .f. will be given by.
`(1)/(f) = (1)/(10) - (1)/(10) + (2)/(100)`
`(1)/(f) = (2)/(100) = (1)/(50) rArr f = 50 cm`
f = + 50 cm (converging lens)