6.9 Uses and dangers of electromagnetic waves
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Which type of electromagnetic wave is used to cook food in a microwave oven?
Choose one answer.
Correct Not quite: the answer is Microwaves
Mark scheme
B: Microwaves
Model answer
Microwaves (B).
Give one use of each of the following: (a) radio waves (b) infrared (c) X-rays.
Mark scheme
(a) broadcasting / communication (1); (b) heating / thermal imaging / remote controls (1); (c) medical imaging / security scanning (1)
Model answer
(a) Broadcasting television. (b) Thermal imaging cameras. (c) Taking images of broken bones.
Explain why X-rays are used to take pictures of bones.
Mark scheme
X-rays pass through soft tissue (1); but are absorbed by dense bone, so bones show up on the detector (1)
Model answer
X-rays pass through soft tissue but are absorbed by bone, so the bones show up on the image.
Explain why a radiographer stands behind a lead screen when taking X-rays.
Mark scheme
X-rays are ionising and can damage cells / cause cancer (1); the radiographer takes many X-rays so repeated exposure increases the risk / lead absorbs X-rays (1)
Model answer
X-rays are ionising and can damage cells or cause cancer. The lead screen absorbs the X-rays, and the radiographer would otherwise be exposed many times.
Describe the harm that ultraviolet radiation can do to the human body, and one way to reduce the risk.
Mark scheme
sunburn / skin cancer / eye damage (1); because UV is ionising and damages DNA (1); use sun cream / wear sunglasses / cover up / stay out of strong sun (1)
Model answer
UV can cause sunburn and skin cancer, because it is ionising and damages DNA. Wearing sun cream reduces the risk.
Explain how a microwave oven heats food.
Mark scheme
microwaves are absorbed by water molecules in the food (1); the energy is transferred to the thermal store of the water / food (1); so the food heats up (1)
Model answer
The microwaves are absorbed by the water in the food. This transfers energy to the thermal store of the water, so the food gets hotter.
Give two reasons why microwaves are used for satellite communications but visible light is not.
Mark scheme
microwaves can pass through the Earth's atmosphere (1); visible light is scattered / absorbed by clouds and weather (1)
Model answer
Microwaves pass through the atmosphere easily, but visible light would be blocked or scattered by clouds.
State which three parts of the electromagnetic spectrum are ionising.
Mark scheme
ultraviolet (1); X-rays and gamma rays (1)
Model answer
Ultraviolet, X-rays and gamma rays.
Evaluate the risks and benefits of using X-rays in medicine.
Mark scheme
benefit: show broken bones / diagnose illness without surgery (1); benefit: can save lives / treat disease (1); risk: ionising, so can damage cells / cause cancer (1); doctors use X-rays only when the benefit outweighs the risk / minimise dose (1)
Model answer
X-rays allow doctors to see broken bones and diagnose illness without surgery, which can save lives. But X-rays are ionising and can damage cells, so they are only used when the benefit is greater than the risk, with the smallest dose possible.
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