Microwaves
3 marks · NormalMicrowave ovens have metal screens on the doors.
Explain why it is important for microwave ovens to have metal screens.
Describe what could happen if a microwave oven did not have a metal screen.
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(a) The metal screen reflects microwaves, preventing them from escaping the oven and causing harm to people outside. It keeps the microwaves inside where they can cook the food safely.
(b) If there were no metal screen, microwaves could leak out and potentially heat or burn body tissue of people nearby.
Common mistakes: Saying the screen keeps 'heat' inside rather than microwaves.
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Marking points
B1 (a) · 1 mark · States microwaves are reflected by the metal screen.
B1 (a) · 1 mark · Explains it prevents microwaves escaping and protects people.
B1 (b) · 1 mark · Correctly describes a possible consequence such as tissue heating or burns.
Worked solution
a) The metal screen reflects microwaves back into the oven so they do not escape. This makes sure the microwaves do not reach outside the oven, protecting people.
b) Without a screen, microwaves could escape and heat or even burn people standing close to the oven.