Microwaves
3 marks · NormalA company is designing a new microwave oven. They want to ensure it is both efficient and safe.
Explain how microwaves heat food inside an oven.
Describe one design feature that makes a microwave oven safe for users.
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(a) Microwaves are absorbed by water molecules in the food, causing them to vibrate faster and increasing the temperature throughout the food.
(b) Metal screen in the door; interlock system to switch off if door is open.
Common mistakes: Not mentioning the absorption by water molecules.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States microwaves are absorbed by water molecules.
B1 (a) · 1 mark · Explains absorption causes molecules to heat/vibrate, heating the food throughout.
B1 (b) · 1 mark · States a valid safety feature (e.g. metal screen, door interlock).
Worked solution
a) The microwaves are absorbed by the water molecules, which then vibrate more rapidly and cause the temperature in the food to rise.
b) Microwave oven has a metal mesh screen in the door that reflects microwaves back into the oven, or an interlock that switches off the magnetron if door is opened.