Final answer:
A pencil in a glass container filled with water appears to be bent due to refraction of light.
Step-by-step explanation:
When light travels from one medium to another, it changes direction due to a phenomenon called refraction. This bending of light is caused by a change in the speed of light when it enters a different medium, such as water. When a pencil is placed in a glass container filled with water, the light from the pencil bends as it passes from the air into the water, creating an illusion that the pencil is bent.
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