Refraction
2 marks · EasyExplain, using wave ideas, why a straight pencil appears bent when it is placed at an angle in a glass of water.
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The light waves change speed as they pass from water to air. This causes them to change direction (refract), so the part of the pencil under water appears at a different position.
Also accept: Light changes direction as it moves from water into air, making the pencil look bent.; Refraction causes the bending effect.
Common mistakes: Light reflects at the water surface.
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Marking points
M1 · 1 mark · Mentions light waves change speed (or slow down/speed up) at the boundary.
M1 · 1 mark · States that this causes a change in direction (refraction), making the pencil appear bent.
Worked solution
Light waves travel at different speeds in water and air. As they pass from water to air, they speed up and change direction (refraction), so the part of the pencil under water seems shifted from the part above, making the pencil appear bent.