Question

How can we explain this change in size of lemon (The in a glass of water appears big than its actual size, when viewed from the side of tumbler)

Answer 1

$\large\blue{heya mate!!}$

lemon in a glass of water appear bigger than its actual size is due to refraction of light". Reason: Light is refracted as it passes from water into air. Here, Tumbler with water acts as convex lens which curves outward in the middle and can focus light rays to magnify object.