Question:
two converging length of power 5 D and 4 D are placed 10cm apart find the focal length and power of this combination.
Answer:
It is given that,
P1 = 5D, So f1 = 1/P1, f1 = 1/5 = 20 cm
P2 = 4D, So f2 = 1/P2, f2 = 1/4 = 25 cm
The focal length of this combination is = F = (f1 x f2)/(f1 + f2) -d
= (20 x 25)/(20 + 25)- 10
= 100/7
= 14.30 cm.
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