Question

if two lenses have focal length of 20cm and -40cm what will be the focal length of combination

Answer 1

focal length of combination is 40

Answer 2

Answer:

Explanation:

Focal length comb.(fc)

1/fc=1/f1+1/f2 ...n

1/fc=f1+f2/f1×f2

Fc=f1×f2/f1+f2

Fc=20×(-40)/20+(-40)

Fc=-800/-20

Fc=40cm