The focal length of a lens suggested to a person with Hypermetropia is 100cm. Find the distance of near point and power of the lens.
Given: The focal length of a lens suggested to a person with Hypermetropia is 100cm.
To find the distance of near point and power of the lens.
Solution:
Let the distance of near point be ’d’ and focal length be 'f=100cm' then
f=25dd−25cm⟹100(d−25)=25d⟹100d−25d=2500⟹d=250075⟹d=1003=33.33cm
Hence the distance of near point will be 33.33cm
We know,
Power, P=1fD, f is in metres
⟹P=1100×10−2⟹P=1D
is the power of the lens.