Question

Two lenses of power + 8 D and - 4D are placed in contact. Find the focal length - of the combination.​

Answer 1

Answer:focal length is 1/4 Explanation: P1=+8D,P2=-4D P=P1+P2 P= 4D F=1/P F=1/4

Answer 2

Given,

Two lenses of power = +8D , -4D.

To Find,

Value of focal length of the combination.

Solution,

We can solve this mathematical problem using mathematical formulas.

According to question,

Power = $\frac{1}{F}$

P₁ = $\frac{1}{F_{1} }$ = $\frac{1}{0.25}$ = 4D

P₂ = $\frac{1}{F_{2} }$ = $\frac{-1}{0.1}$ = -10D

So, Power of combination,

P = P₁ + P₂

⇒ 4D + (-10D)

⇒ -6D

Focal length of combination,

F = $\frac{1}{P}$ = $\frac{1}{-6}$ = -0.666m = 16.66cm

⇒ The combination has negative focal length, so its is diveging.

Hence, The focal length of the combination is 16.66 cm.