Question

A point object is placed 20 cm left of a convex lens of focal length f = 5 cm (see the figure). The lens is made to oscillate with small amplitude A along the horizontal axis. The image of the object will also oscillate along the axis with

(A) a mplitude A/9, out of phase with the oscillation of the lens

(B)  amplitude A/3, out of phase with the oscillations of the lens. 

(C)  amplitude A/3, in phase with the oscillations of the lens 

(D)  amplitude A/9, in phase with the oscillations of the lens 

Answer 1

Correct option  (A) amplitude A/9, out of phase with the oscillation of the lens. 

Explanation:

As lens is oscillating with small amplitude A.

:. Image will oscillate with m²A

When lens move left then O will come near to lens thus I will go away. Thus image is oscillating out of phase with respect to lens.

m = 5/5 - 20 = 5/-15 = -1/3

Amplitude of image = (1/3)² A = A/9