1. 6.8 Below the visible
28 January 2015
Name the types of
electromagnetic
radiation with
wavelengths greater than
visible light

2. Aims
• Describe the electromagnetic radiation with
wavelengths longer than visible light
• Use the wave model to explain the behaviour
of waves

5. Radio waves

6. Radiowaves
• Communications: TV, mobile phones, local
radio, police

7. Microwaves

8. Microwaves
• Microwaves ovens, communicating with
satellites, RADAR

9. How do microwave ovens work?
• Microwaves are produced by a magnetron
• Reflected by metal on the inside of the oven
• Absorbed by the food
• Not very good absorption so they go through
the food rather than be absorbed by the
surface

10. Microwave communication

12. Infra-red

13. Infra-red
• Search and rescue teams, detect circulation
problems, (cancer, arthritis), astronomy,
burglar alarms

20. Questions
• Light, long-wavelength infrared, short-
wavelength infrared
• Which of the above:
– Can be detected by the human eye?
– Can pass through glass?
– Is emitted by red hot objects?

21. Questions
• Explain why a metal bar starts to glow red when
it is heated up
• Infra-red has a heating effect on most solids.
What does this tell you about whether this
radiation is reflected, transmitted or absorbed
• A TV remote control emits an infrared beam that
carries coded information to the TV set. Explain
how you might use this to find out which
everyday material absorb infrared and which
transmit it.
• List three uses of microwaves.