Question

Find the focal length of a lens of power 2 d what types of lens is this

Answer 1

Given: The power of the lens (P) = 2 d
Since power of the lens has positive sign. Hence, the nature of the lens will be convex type.
Let the focal length of the given lens be 'F'. 
Concept: The relation between 'P' and 'F' is given as 
                  F = 1 / P
The lens having power 1 d always has focal length of 100 cm.
Now, we shall calculate the focal length of given lens.
                 F = 1 / 2 d
Or,            F = [ 1 / (2 / 100)] cm
Or,            F = 50 cm
Hence, the focal length of the lens will be 50 cm and it will be convex type.

Answer 2

Answer:

Given: the power of lens (p)=2d

Change power of the lens has positive sign. Hence, the nature of lens will be convex type, let the focal length of the given lens be 'F'.

F=1/p

The lens having power 1d always has focal length of 100cm.

Now,

F=1/2d

F={1/(2/100)} cm

F=50cm

Hence, the focal length of the lens will be 50 cm and it will be convex type.

Explanation:

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