Question

A convex lens of power +6d is placed in contact with concave lens of power -4d what is the nature and focal length of the combination

Answer 1

total power = 6d-4d = 2d

nature of this combination is convex

p = 1/f

2=1/f

f=0.5m=50cm

Answer 2

Answer:

The focal length of the combination is 50 cm and this lens is convex lens.

Explanation:

Given that,

Power of convex lens $P_{1}= +6 D$

Power of concave lens$P_{2} = -4 D$

We know that,

The Power of the lens is the reciprocal of the focal length of the lens.

$P=\dfrac{100}{f}$

The Power of the combination is

$P=P_{1}+P_{2}$

$P = 6-4$

$P =2 D$

The focal length of the combination is

$f = \dfrac{100}{P}$

$f = \dfrac{100}{2}$

$f =50\ cm$

Hence, The focal length of the combination is 50 cm and this lens is convex lens.