Question

two thin lenses of focal length 10cm and 20cm are placed in contract calculate the effective power of the combination​

Answer 1

20/3

Step-by-step explanation:

We can use the formula : 1/R1 + 1/R2 = 1/f here
Therefore 1/10 + 1/20 = 3/20
And as it is 1/f its reciprocal will be 20/3