Question

Two lenses of power 2.5D and 1.5D are joined together .The focal length of the new lens formed is

Answer 1

Given

Two lenses of power 2.5 D and 1.5 D are joined together

To Find

The focal length of the new lens formed

Solution

Power of the combination of lenses = 2.5 + 1.5

⇒ P = 4 D

Now , Focal length is the reciprocal of power .

$\implies \rm f=\dfrac{1}{P}\\\\\implies \rm f=\dfrac{1}{4}\\\\\implies \bf f=0.25\ m$

So , focal length of the new lens formed is 0.25 m

Answer 2

Answer:

Given

Two lenses of power 2.5 D and 1.5 D are joined together

To Find

The focal length of the new lens formed

Solution

Power of the combination of lenses = 2.5 + 1.5

⇒ P = 4 D

Now , Focal length is the reciprocal of power .

$\begin{gathered}\implies \rm f=\dfrac{1}{P}\\\\\implies \rm f=\dfrac{1}{4}\\\\\implies \bf \red {f=0.25\ m}\end{gathered} </p><p>$

So , focal length of the new lens formed is 0.25 m