1.8 Microwaves & Infrared

Question 1

What two groups of microwaves are there?

Answer 1

• Ones that aren’t absorbed by water molecules
• Ones that are absorbed by water molecules

Question 2

What is an example of a microwave that isnt absorbed by water molecules?

Answer 2

• Microwaves for communication, once the microwaves make it through the atmosphere they are received by a satellite and then transmitted back onto earth using a satellite dish to get things like satellite TV

Question 3

Why are some microwaves not absorbed by water molecules?

Answer 3

Because they have to pass through the atmosphere to reach the satellite and the atmosphere contains a lot of water

Question 4

What is the type of microwave that is absorbed by water molecules?

Answer 4

In microwave ovens to heat our food

Question 5

How do microwave ovens heat our food?

Answer 5

When the microwaves are fired at the food, the energy from those waves is absorbed by all the water molecules. As the water molecules start to vibrate more, they transfer energy to neighbouring molecules so that it spreads throughout the food via conduction and convection

Question 6

What is infrared radiation emitted from?

Answer 6

From all objects that have thermal energy

Question 7

What can detect IR radiation?

Answer 7

Infrared cameras can detect IR radiation and monitor temperature. They detect the IR and turn it into an electrical signal, which is displayed on a screen as a picture. The hotter an object, the brighter it appears

Question 8

What is an example of a use for infrared radiation?

Answer 8

• Cooking: By heating metal to very high temperatures, we can make the metal emit lots of infrared radiation which can then heat our food by transferring heat energy causing it to cook

Question 9

How is cooking food with IR radiation different to cooking food with microwaves?

Answer 9

IR radiation doesn’t penetrate the surface of the food. This is why bread toasts in a toaster rather than just getting generally warmer like it would in a microwave

Question 10

How is IR radiation used in electric heaters?

Answer 10

These devices use electrical energy to heat the metal of the heater and then because its so hot it emits IR radiation to the surroundings which is able to heat up our rooms