(a) What do you understand by the power of a lens? Name one factor on which the power of a lens depends.
(b) What is the unit of power of a lens? Define the unit of power of a lens.
(c) A combination of lenses for a camera contains two converging lenses of focal lengths 20 cm and 40 cm and a diverging lens of focal length 50 cm. Find the power and focal length of the combination.
(a) Th ability of a lens to converge/diverge a beam of light rays is known as its power. It is defined as the reciprocal of the focal length.
Power depends on focal length.
b) The SI unit of power of a lens is Dioptre. It is denoted by the letter "D". 1 dioptre is the power of a lens of focal length 1 m.
1 D=11 m
c) Here, f1=20 cm, f2=40 cm and f3=−50 cm
Peq=1feq in metres=10.18=5.55 D