Question

The power of a plano-convex lens is P. If this lens is cut longitudinally along its principal axis into two equal parts then the power of the each part is

Answer 1

Answer:

The power of a plano-convex lens is given as “P”.

Let the plano-convex lens be a combination of lens A & lens B as shown in the first image of the figure attached below.

Now, if we cut this plano-convex lens longitudinally along its principal axis into 2 equal parts just as shown in the 2nd image of the figure attached below, then the radius of curvature of lens A & lens B remains the same.  

∴ The focal length of lens A = The focal length of lens B ….. (i)

We know, the formula for power is given as,

P = 1/f ….. (ii)

Therefore, from (i) & (ii), we get

Power of lens A = Power of lens B = P

Thus, the power of each part is P.