Refraction
3 marks · EasyA student observes a pencil in a glass of water. The pencil appears bent at the surface of the water.
Explain, using the idea of refraction, why the pencil appears bent.
What happens to the light as it leaves the water and enters the air?
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(a) Light bends (changes direction) as it leaves water and goes into air, making the pencil appear bent at the surface. · must show Refraction at boundary, Direction changes/appears bent
(b) The light speeds up as it leaves the water and enters air. · must show Light speeds up
Must show: Light bends as it leaves water, Change of direction causes pencil to look bent, Light speeds up leaving water
Common mistakes: Describing absorption or reflection instead
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Mentions light bends (changes direction) at the water-air boundary.
B2 (a) · 1 mark · States this causes apparent bending of the pencil.
B3 (b) · 1 mark · States the light speeds up as it leaves water into air.
Worked solution
a) As light leaves the water and enters the air, it bends away from the normal because it speeds up. This bending makes the pencil look bent at the surface.
b) The light speeds up as it enters air from water.