Microwaves and infrared Flashcards
1
Q
What are the characteristics of microwaves and infrared
A
- Microwaves and infrared radiation (IR) are second and third on the EM spectrum
- They both have long wavelengths and short frequencies
2
Q
What are microwaves that aren’t absorbed by water used for
A
- Used to send and receive information from satelites
- This is because mirowaves can penetrate the Earth’s atmosphere
- As the Earth’s atmosphere contains many water molecules, we must make sure that the waves are not absorbed by them
- When the satelite receives information and transmits it back to Earth (using microwaves), we receive it using satlite dishes
- This is used in satelite TV
3
Q
What are microwaves that are absorbed by water used for
A
- Used in microwave ovens
- Microwaves are emitted which are absorbed by water molecules in the food. As they have more energy, they vibrate more. This passes energy on to neighbouring molecules which heats up the food (heat spreads through conduction and convection)
4
Q
What is infrared radiation
A
- Emitted by all objects that have thermal energy
- The hotter the object, the more infrared radiation is emitted
5
Q
How do infrared cameras work
A
- Helps us to see in the dark
- Captures infrared radiation emitted by all objects
- Allows us to see living organisms as they are hotter than their surroundings and therefore, they emit more infrared radiation
6
Q
How is infrarred used in cooking
A
- Metal is heated to high temperatures (in ovens and grills)
- Metal emits lots of infrared radiation
- This radiation is absorbed by the food and added to its thermal energy store. This inturn heats up the food
- IR doesn’t penetrate the surface of the food (bread becomes toast rather than just heating up)
7
Q
When is IR and microwaves harmful
A
- Only harmful in large quantities
- E.G: putting a living organism inside a microwave oven
8
Q
Why can we use infrared radiation in optical fibre communication?
A
- Because they can undergo total internal reflection
