Problem 10.3. Two converging lenses of focal lengths 40 cm and 50 cm are placed in contact. What is the focal length of this lens combination? What is the power of the combination in diopters?
Data .
Focal length of first lens.f1 =40cm
Focal length of 2nd lens f2= 50cm
To find .
Focal length of combination f=?
Power of combination p=?
Solution.
Using the combination of lens formula
1/f= 1/f1 +1/f2. =1/40 + 1/50
5+4/200 =9/200
22.2cm
Ans
Power of lens is given by p = 1/f = 1/22.2× 10-²m =100/22 5 = 4.5 diopters answer
