6.8 Below the visibleApril 12, 2023

Name the types of electromagnetic

radiation with wavelengths greater than

visible light

Aims

• Describe the electromagnetic radiation with wavelengths longer than visible light

• Use the wave model to explain the behaviour of waves

http://upload.wikimedia.org/wikipedia/commons/c/cf/EM_Spectrum_Properties_edit.svg

http://upload.wikimedia.org/wikipedia/commons/3/34/Atmospheric_electromagnetic_opacity.svg

Radio waves

Accelerated electrons

Radiowaves

• Communications: TV, mobile phones, local radio, police

Microwaves

Molecular transitions

Microwaves

• Microwaves ovens, communicating with satellites, RADAR

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

Microwave communication

Infra-red

Molecular transitions

Infra-red

• Search and rescue teams, detect circulation problems, (cancer, arthritis), astronomy, burglar alarms

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?

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.