P13 - EM Waves Flashcards
EM spectrum in order (starting with longest wavelength)
Radio waves, Microwaves, Infrared, Visible light, Ultraviolet radiation, X rays and gamma radiation
Radio waves wavelength
Kilometres
Microwaves wavelength
Between kilometres and millimetres
Infrared wavelength
Millimetres
Visible light
Between millimetres and nanometres
Ultraviolet radiation
Between Nanometres and picometres
X-rays and gamma radiation
Picometres
What properties do EM waves share?
They are all transverse waves
They can travel in a vacuum
They travel at 3 x 10^8 m/s
What is increasing energy proportional to on the EM spectrum?
Increasing frequency
What is increasing energy inversely proportional to on the EM spectrum?
Increasing wavelength
Wave speed equation
Wave speed (m/s) = frequency (Hz) x Wavelength (m)
P13 RP : To investigate which materials emit the most infrared radiation ( method)
Method
1. Fill a kettle with an appropriate amount of water
2. Boil the kettle
3. Place a heat proof mat underneath a Leslie Cube(each side with a different material)
4. Fill the Leslie Cube with boiling water
5. Measure 10cm from one side of the Leslie Cube ( directly in the middle)
6. From 10cm use an infra red thermometer to measure the temperature
7. Record the temperature
8. Change the side and repeat steps 5 to 7.
The shorter the wavelength of the wave…
- The more information carried
- The shorter the range (greater absorption by the atmosphere)
- The less they spread out.
Which objects emit more infrared radiation?
Hotter objects
Which surfaces absorb more infrared radiation?
Dark, Matte Black surfaces
Which part of the EM spectrum do optical fibres use and why?
Optical fibres in communications systems usually use infrared radiation instead of visible light. This is because infrared radiation is absorbed less than visible light in the glass fibres.
How do microwaves heat food?
Microwaves penetrate into food and are absorbed by the water molecules in the food, heating it
Why can microwaves and radio waves be hazardous?
Because they penetrate people’s bodies and can heat the internal parts of the body.
Why might children be more affected than adults by Electromagnetic radiation?
Because children have thinner skulls than adults there brains might be more affected by mobile phone radiation.
What are optical fibres?
Very thin glass fibres. They are used to transmit signals carried by light or infrared radiation.
Why can’t the light rays escape from the optical fibres?
When they reach the surface of the fibre, they are reflected back into the fibre.
Differences between optical fibres and radio waves, microwaves
Optical fibres carry much more information as light has a much shorter wavelength than radio waves and so can carry more pulses of waves
Optical fibres are more secure because the signals stay in the fibre
Hazards of Ultraviolet Waves
They are harmful to human eyes and can cause blindness
Harmful to skin- can cause sunburn and skin cancer
Ways to protect against Ultraviolet Waves
Use skin creams to block UV waves
If in a sunbed wear special googles to protect your eyes
Similarities between X-rays and gamma rays
Short wavelength end of the EM spectrum
Carry much more energy per second than longer-wavelength EM waves
Differences between X-rays and Gamma rays
• X-rays are produced when electrons or other particles moving at high speeds are stopped - X-ray tubes are used to produce X-rays
gamma rays are produced by radioactive substances when unstable
nuclei release energy
•
gamma rays have shorter wavelengths than X-rays, so they can penetrate substances more than X-rays can.
Uses of Gamma rays
Exposing food to gamma rays kills 99% of disease- carrying organisms
Exposing surgical instruments to gamma rays kills any bacteria on the instruments
Doctors use Gamma ray therapy to destroy cancaerous tumours
What is ionisation?
When atoms become charged because they lose electrons.
What are examples of ionising radiation?
X-rays and gamma rays
What can ionisation do?
If ionisation happens to a living cell, it can damage or kill the cell. For this reason, exposure to too many X-rays or gamma rays is dangerous and can cause cancer. High doses kill living cells, and low doses cause gene mutation and cancerous growth.
Safety measures against ionising radiation
People who use equipment or substances that produce any form of
ionising radiation (e.g., X-rays or gamma rays) must wear a film badge. If
the badge shows that it is over-exposed to ionising radiation, its wearer is
not allowed to continue working with the equipment for a period of time.
How do X-rays travel through the body?
X-rays pass through soft tissue but are absorbed by bones (also teeth and some metal objects)
What does the radiation dose depend on?
Type of radiation used
How long the body is exposed to it
The energy per second absorbed by the body from the radiation
What is radiation dose measured in?
Sieverts (Sv)
What is X-ray therapy?
Doctors use X-ray therapy to destroy cancerous tumours in the body.
How does X-ray therapy work?
Thick plates between the X-ray tube and the body stop X-rays from reaching healthy body tissues. A gap between the plates allows X-rays through to reach the tumour
X rays for therapy wavlength
Shorter in wavelength than X-rays used for imaging
How do X rays work?
In an X-ray tube when fast-moving electrons hit a target.
