Question

An eye specialist prescribes spectacles having a combination of convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. The power of this lens combination in dioptres is 1) +1.5 2) –1.5 3) +6.67 4) –6.67

Answer 1

Text Solution

(♡˙︶˙♡)

Answer : +1.5

-1.5

+6.67

-6.67

Solution

F1 = 40cm

= 0.4m

F2 = -25

= 0.25m

( F )

1/f = 1/f1 + 1/f2

= 1/0.40 - 1/0.25

= 0.25 - 0.4 / 0.40 x 0.25

= - 0.15/ 01 = - 1.15 D

=> P = 1/f = - 1.5 D

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