P1.12/13 - Cooking/Communication with waves

Question 1

Name two things you may cook with electromagnetic waves?

Answer 1

• Toast (infrared radiation)

- Grilling some bacon (infrared radiation)

Question 2

What is infrared radiation emitted by?

Answer 2

It is emitted by warm objects. The warm the object the infrared radiation it emits.

Question 3

What happens when something absorbs infrared radiation?

Answer 3

When something absorbs infrared radiation it surface gets hotter. This is the heat you feel from an open flame. These two effects make infrared useful for cooking.

Question 4

How does a toaster cook food?

Answer 4

As the toaster gets hotter it emits more and more infrared radiation. It gets so hot it even emits some red light. The infrared waves from the toaster are then absorbed by the food. This heats up the surface of the food so it gets cooked.

Question 5

Why do most toasters have a shiny surface at the bottom?

Answer 5

The shiny surface reflects infrared radiation back onto the food which helps it cook faster.

Question 6

What type of waves do microwaves produce to cook food?

Answer 6

Mircrowaves

Question 7

How do microwaves heat food?

Answer 7

Instead of heating just the surface like infrared radiation, it heats 1cm into the food. The microwaves are absorbs by fat and water in the food. This causes the food to heat up.

Question 8

Why are there shiny metal surfaces inside a microwave?

Answer 8

They shiny surfaces reflect the microwaves to make sure all parts of the food gets cooked. It helps to make sure the food is fully cooked.

Question 9

Microwaves can cause tiny burns to humans. How are microwaves prevented from leaving the microwave?

Answer 9

A metal mesh is placed inside the oven door.

Question 10

How is energy transferred when cooking using infrared and microwaves?

Answer 10

The energy is transferred from the electromagnetic waves to the molecules inside or on the food. This energy is then transferred to the rest of the food through conduction or convection. In microwaves, the fat and water molecules gain kinetic energy as they absorb the microwaves. In the case of infrared, only the molecules on the surface gain kinetic energy.

The energy associated with both infrared and microwaves depends on how many waves there are per second (the frequency).

Question 11

What feature of electromagnetic waves makes them very useful for communication?

Answer 11

Electromagnetic waves travel very fast.

Question 12

What electromagnetic wave do mobile phones use to communicate?

Answer 12

Microwaves

Question 13

What are a few disadvantages of using microwaves?

Answer 13

• Microwaves need a clear line of sight between the phone (transmitter) and the phone mast (receiver) since they travel in a straight line. Microwaves travel is straight lines and sometimes hills or buildings get in the way.
• Microwaves are also effected by poor weather conditions.

Question 14

Gives two reasons for signal loss when using microwaves

Answer 14

• Radio waves spread out when travelling through gaps or around obstacles. Microwaves do not spread out much so line of sight is even more important. If there is not a good line of sight it can lead to signal loss.
• Other electromagnetic waves can interfere with the microwaves.

Question 15

How can you reduce interference from other electromagnetic waves when using microwaves?

Answer 15

• Microwave transmitters are usually placed close together to ensure the signal received remains strong.
• The transmitters are usually placed high up on hills to avoid other obstructions.

Question 16

Describe one risk from using mobile phones in terms of electromagnetic waves

Answer 16

Microwaves can cause a small heating effect on the brain, research shows. The NHS guidelines suggest mobile phones should not be used by younger children.