Question

what is the focal length of corrective lens in the centermetre who's power is -5D? what kind of lens is this?​

Answer 1

Given:-

• Power of Lens ,P = -5 D

To Find:-

• Focal length ,f

• Which type of lens is this ?

Solution:-

As we know that Power of a lens is defined as the reciprocal of its focal length.

• P = 1/f

where,

P is the Power of Lens

f is the focal length

Substitute the value we get

→ -5 = 1/f

→ f = 1/-5

→ f = -1/5

→ f = -0.2 m

→ f = 0.2 × 100cm = -20 cm

Therefore,the focal length of the lens is 20 cm.

Here, the focal length of the lens is in negative so, the lens will be concave lens.

Answer 2

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what is the focal length of corrective lens in the centermetre who's power is -5D? what kind of lens is this?

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• $Lens\: power(P) =5 D$

${ { \underbrace{ \mathbb{ \red{To\:PrOvE\ }}}}}$

• $Focal\:length (f)$
• $Type\:of\:lens$

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${\boxed {\boxed {P=\frac{1}{f}}}}$

• $P=power\: of \:lens$
• $f=Focal\: length$

$Substitute \:the \:values$

$- 5=\frac{1}{f}$

$f=\frac{1}{-5}$

$f=\frac{-1}{5}$

$f=-0.2m$

$f=-0.2\times 100$

${\boxed {\boxed {f=-20cm}}}$

$\therefore Focal\:length\:of\:lens\:is{\boxed {\boxed {- 20cm}}}$

$\therefore It\:is\:{\boxed {concave}} \: mirror$

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