Question

(c) A convex lens of focal length 25 cm and
a concave lens of focal length 10 cm
are placed in close contact with each
other. Calculate the lens power of this
combination
​

Answer 1

Explanation:

focal length:the distance between the centre of a lens or curved mirror and its focus.

the equivalent distance in a compound lens or telescope.

Optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device: P = 1/f.

p=1/0.25d

p=4d

p=-1/0.10

p=-10d

combination

p=4-10

p=-6D

Answer 2

Explanation:

CONVEX LENS

$f = 0.25m$

so

$p = \frac{1}{0.25}$

p=4

CONCAVE LENS

$f = - 0.1m$

so

$p = - \frac{1}{0.1}$

so

p=. -10D

power of combination = 4+(-10)

4-10=-6D

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