Two convex lenses of focal length 20 cm each are placed coaxially with a separation of 60 cm between them. The image of the distant object formed by the combination is at_____cm from the first lens.

Question

Accepted Answer

Correct answer: 100. (100) Let L_1 be the first lens and L_2 be the second lens. The first refraction is in L_1. Using lens formula, u_1=∞,f_1=2 0 c m, 1v_1−0= 1f_1 ⇒v_1=2 0 c m Hence, the distance between the second image and the L_2 would be (60 - 20)= 40 cm. For the second lens L_2, u_2= -40 cm, f_2 = 20 cm, 1v_2− 1u_2= 1f_2 ⇒ 1v_2+ 14 0= 12 0 ⇒ 1v_2= 14 0 ⇒ v_2 = 40 cm So, the distance of image from first lens is x = 40 cm + 60 cm = 100 cm

$Two convex lenses of focal length 20 cm each are placed coaxially with a separation of 60 cm between them. The image of the distant object formed by the combination is at_____cm from the first lens.$

Solution

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