Cooking and communicating using waves

Question 1

Penetration of infrared radiation and microwaves in food.

Answer 1

• Infrared radiation does not penetrate food very easily.
• Microwaves penetrate up to 1 cm into food.

Question 2

Energy is transferred by waves:

Answer 2

• The amount of energy depends on the frequency or wavelength of the wave
• High frequency (short wavelength) waves transfer more energy.

Question 3

Normal ovens cook food by infrared radiation:

Answer 3

• Energy is absorbed by the particles on the surface of food.
• The kinetic energy of the surface food particles increases
• The rest of the food is heated by conduction.

Question 4

Microwave ovens cook food by microwave radiation:

Answer 4

The water or fat molecules in the outer layers of food vibrate more, and kinetic energy increases.

Question 5

Microwave properties

Answer 5

• Microwaves have wavelengths between 1 mm and 30 cm.
• Mobile phones use longer wavelengths than microwave ovens.
  
  • Less energy is transferred by mobile phones.

Question 6

How is microwave radiation used?

Answer 6

Microwave radiation is used to communicate over long distances.

Question 7

What is one of the necessities of microwave communication?

Answer 7

• The transmitter and receiver must be in line of sight.
• Aerials are normally situated on the top of high buildings.

Question 8

Satellites are used for microwave communication.

Answer 8

• The signal from Earth is received, amplified and re-transmitted back to Earth.
• Satellites are in line of sight because there are no obstructions in space.
• Large aerials can handle thousands of phone calls and television channels at once.

Question 9

What are the concerns about microwave communication?

Answer 9

There are concerns about the use of mobile phones and where phone masts are situated. Scientists publish results of their studies to allow others to check their findings.

Question 10

Why does the signal strength for mobile phones change a lot over a short distance?

Answer 10

• Microwaves do not show much diffraction.
• Adverse weather and large areas of water can scatter the signals.
• The curvature of the Earth limits the line of sight so transmitters have to be on tall buildings or close together.

Question 11

What is a problem with mobile phones?

Answer 11

• Mobile phones can interfere with sensitive equipment.
• They are banned on planes and in many hospitals.

Question 12

Microwaves can:

Answer 12

• Penetrate glass or plastic but are reflected by shiny metal surfaces:
  
  • special glass in a microwave oven door reflects microwaves.
  • They can cause body tissue to burn.