place a spoon in an upright position in a round glass of water. Now, move it slowly from the middle of the glass to the side. You will see that spoon appears to get bend or broken. This illusion occurs because of a phenomenon called the refraction of light.
Refraction takes place when light passes at an angle from one transparent medium to another, for example from air to water.
We know that light travels in a straight line, but when a ray of light hits the water at an angle, its speed changes. This cause a change in direction. So, the light is bent- and then continues in a straight line.
When the spoon is straight up in the glass, it appears straight , because when light hits the water square on, it will pass straight through, and will not be refracted or bent. So, there is no distortion . However, when we move the spoon sideways, the light from the spoon hits the water at an angle so it is refracted or bent, and the part of the spoon under water appears in an different location. The result is the illusion of a bent spoon.