P13: Electromagnetic waves Flashcards
What are the uses of radio waves?
Transmit radio and terrestrial (Not satellite or cable, but received using an aerial) TV signals.
Used because they can travel long distances before being absorbed e.g. by buildings or trees.
Longer wavelength waves can also diffract between hills.
They can reflect off of a layer of charged particles in the atmosphere (ionosphere), allowing us to send radio waves long distances around the Earth.
What are the uses of micro waves?
To heat food - most foods contain water molecules, which absorb the energy of microwaves, causing the temperature of the food to increase.
Used to communicate with satellites in space as they can pass through the Earth’s atmosphere without being reflected or refracted.
What are the uses of infrared?
Emitted by electrical heaters and used to cook food in ovens, because energy of infrared is easily absorbed by objects, increasing their temperature.
Used in infrared cameras e.g. for checking heat loss of a building.
What are the uses of visible light waves?
Communication using optical fibres (thin strands of glass). Pulses of light can be transmitted down the fibres and used to carry information. They carry telephone and TV signals.
Visible light can carry a great deal of information because it has a short wavelength.
What are the uses of UV waves?
Energy efficient light bulbs. UV light is created inside the bulb - because it has a short wavelength, it carries more energy than visible light. The energy of the UV is absorbed by the internal surface of the bulb and converted to visible light. This requires less energy than a normal light bulb.
Sun tanning beds - can increase risk of skin cancer and cause premature skin ageing.
What are the uses of X-rays?
Medical imaging - used to visualise broken bones.
Penetrative - easily pass through body tissue.
Absorbed by bones.
Medical treatments.
What are the uses of Gamma rays?
Medical imaging - used to detect cancers.
Penetrative - easily pass through body tissue.
Radiotherapy for cancer
What are electromagnetic waves?
Transverse waves that transfer energy from the source of the waves to an absorber e.g. a microwave.
What happens to wavelength and frequency as you move to the right of the EM spectrum?
Wavelength decreases
Frequency increases
List the electromagnetic spectrum
Radio waves (lowest frequency, longest wavelength)
Microwaves
Infrared
Visible light
UV light
X rays
Gamma rays (highest frequency, shortest wavelength)
What is a continuous spectrum?
The cut-off point between one type of wave and another is unclear (EM spectrum is continuous)
What do EM waves travel through?
No need for medium - can travel through a vacuum.
What is the speed of EM waves in a vacuum?
3*10^8 m/s
What happens to EM waves when passing through different materials?
Either absorbed, reflected or transmitted.
What happens to them depends on the material.
