A lemon kept in water in a glass tumbler appears to be larger than its actual size. It is because of

Light appears to travel in a straight line because –

The reason for a swimming pool to appear less deep than the actual depth is -

The sun is visible to us a few minutes before the actual sunrise because of :

If the lens power of glass is +2 dioptre, its focal length will be-

Two glass lenses of same focal length, one being convex and the other concave, are kept in contact, the combination will act as :