Question

What are the defects vision? A person needs a lens of power-5.5 dioptresfor correcting his distant vision. for correcting his near vision. he needs a lens of power +1.5 dioptres . what is the focal length of the lens required for correcting distant vision?​

Answer 1

Explanation:

Power of the lens for correcting the distant vision = -5.5 Dioptres

Power of the lens for correcting the near vision = +1.5 Dioptres

Now,

We know that the Power of the lens is given by,

\begin{lgathered}Power, P=\frac{1}{f}\\-5.5=\frac{1}{f}\\f=-0.1818\,m\end{lgathered}

Power,P=

f

1

−5.5=

f

1

f=−0.1818m

Therefore, the Focal length of the lens is given by,

Focal length, f = -0.1818 m

(ii).

The Power of lens for near vision = +1.5 Dioptres

So,

The focal length of the lens is given by,

\begin{lgathered}f=\frac{1}{P}\\f=\frac{1}{1.5}\\f=0.66\,m\end{lgathered}

f=

P

1

f=

1.5

1

f=0.66m

Therefore, the Focal length of the lens is given by,

Focal length, f = 0.66 m