What optical illusion is observed when a pencil is placed in water?

• A. The pencil appears straight
• B. The pencil appears broken
• C. The pencil appears magnified
• D. The pencil appears submerged

Answer: (B)

The optical illusion observed when a pencil is placed in water is that the pencil appears broken. This phenomenon is a result of refraction, which is the bending of light as it passes from one medium to another, in this case, from air into water. The light rays that reflect from the pencil bend at the water's surface due to the difference in optical density between air and water.

As a result, the portion of the pencil that is submerged appears to be at a different angle than the part that is above the water. This bending effect creates the illusion that the pencil is discontinuous or 'broken' at the water's surface. The perception of the pencil being straight, magnified, or submerged does not specifically address this refraction effect and does not accurately describe what occurs in this scenario.