6.8 below the visible
TRANSCRIPT
6.8 Below the visibleApril 15, 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
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.