After the space is filled with liquid, the waves are reflected from the lower surface of the lens in the same way as from the upper surface of the plane glass (both waves are reflected from optically denser medium). Therefore, in reflected light, a bright spot will appear at the centre of the rings instead of the dark spot, which was the case before the space between the plane glass and the lens was filled with liquid. Because of the decrease in the velocity of propagation of light in the space between the plane glass and the lens, there occurs a shift and change in the width of the rings. The rings become narrower and more dense.
