Question

The far point distance of a short sighted person is 1.5 m. Find focal length, power and nature

Answer 1

$\huge\underline\blue{\rm Answer:}$

$\large\red{\boxed{\sf Focal\:Lenght(f)=-150cm }}$

$\large\red{\boxed{\sf Power\:of\:Lens=-0.66\:D }}$

• Lens is Concave because power of lens is Negative (-)

$\huge\underline\blue{\rm Solution :}$

$\large\underline\pink{\rm Given: }$

• Far point distance of a short sighted person is (d) = 1.5 m

$\large\underline\pink{\rm To\:Find: }$

• Focal lenght (f) = ?

• Power of lens (P) = ?

• Nature of lens = ?

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$\Large\underline{\underline{\tt 1.Focal\:Lenght(f):}}$

$\Large{\boxed{\sf Focal\:Lenght (f)= -d}}$

$\large\implies{\sf f=-1.5m}$

In centimetre

$\large\implies{\sf f=-1.5×100}$

$\large\implies{\sf f=-150cm}$

$\Huge\red{♡}$$\large\red{\boxed{\sf Focal\:Lenght(f)=-150cm }}$

$\Large\underline{\underline{\tt 2.Power\:of\:lens (P) }}$

We know ,

$\Large{\boxed{\sf Power={\frac{1}{f}}}}$

To calculate power of lens focal length is always taken in meter .

$\large\implies{\sf P=-{\frac{1}{1.5}}}$

$\large\implies{\sf P=-0.66 Diopter }$

$\Huge\red{♡}$$\large\red{\boxed{\sf Power\:of\:Lens=-0.66\:D }}$

$\Large\underline{\underline{\sf 3.Nature\:of\:lens :}}$

Lens is Concave because power of lens is Negative (-)

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If power of lens is Positive (+) then lens must be Convex