Question

A lens X has f=20cm and a lens Y has f=40cm . which lens would u select to obtain a more convergent beam of light ?

Answer 1

i will choose Y because the focus is more in it and i may get a more convergent beam of light

Answer 2

ANSWER↓

Since ,Power of a lens is inversely proportional to the focal length of a lens. The lens having a shorter focal length .i.e., lens Y would obtain more convergent beam of light

P = 1/f

focal length of lens X = 40cm = 40/100 m

power of lens X = 1/ 40/100 =100/40 = 10/4 = 2.5 D

focal length of lens Y = 20 cm = 20/100 m

power of lens Y = 1/20 /100 = 100/20 = 5 D

power of lens Y > power of lens X