Question

Why does a lemon kept in water in a glass tumbler appear to be bigger than its actual size?

Answer 1

This occurs due to the refraction of light. When light travels from one medium (air) to the next (water), it bends away from the original path i.e. it refracts. This  deviation of light from its straight line path upon entering a different medium from its source is known as refraction. As light bends when it enters the water contained in the tumbler, the object appears larger than its actual size.