Electromagnetic Waves
Radio waves
How are radio waves produced?
Radio waves are produced when electrons oscillate in conductors.
For example:
- An alternating current flows through a transmitting antenna.
- The electrons in the antenna oscillate backwards and forwards.
- This produces changing electric and magnetic fields.
- These fields travel away from the antenna as electromagnetic waves.
Uses of Radio waves
- Radio broadcasting: transmitting radio programmes over long distances.
- Television broadcasting: transmitting television signals.
- Communication: communicating between ships, aircraft and other radio systems.
Possible harm
Radio waves are non-ionising radiation.
- At sufficiently high intensities, they can heat body tissues.
- Excessive exposure to powerful radio transmitters may cause harmful heating.
Microwaves
How are microwaves produced?
Microwaves are also produced when electrons oscillate in conductors. However these oscillations are of a higher frequency than the oscillations that produce radio waves.
For example:
- A high frequency alternating electrical current flows through a microwave transmitter.
- Electrons oscillate in the conductor.
- This produces changing electric and magnetic fields.
- These fields travel away as electromagnetic waves.
In a microwave oven, a device called a magnetron produces microwaves.
Uses
- Cooking food: Microwaves are absorbed by water molecules in food, causing heating.
- Satellite communication: Carry signals between satellites and ground stations.
- Mobile phone communication: Mobile phones use microwaves to transmit and receive signals.
- Radar: Used to detect objects and measure their distance and movement.
Possible harm
Microwaves are non-ionising radiation.
- They can be absorbed by body tissues.
- They can cause heating.
- Excessive exposure can cause burns and damage internal tissues.
Infrared radiation
How is infrared radiation produced?
Infrared radiation is emitted by objects because of their thermal energy. As an object becomes hotter, it generally emits more infrared radiation.
Examples include radiators, warm human bodies, hot ovens and fires.
Uses
- Thermal imaging: detecting infrared radiation emitted by objects.
- Remote controls: transmitting signals to televisions and other devices.
- Heaters: transferring energy to objects and people.
- Night vision: detecting infrared radiation from objects.
Possible harm
- Excessive exposure can cause skin burns.
- Intense infrared radiation can damage the eyes.
- Powerful sources can cause overheating.
Visible light
How is visible light produced?
Visible light is produced by hot objects and by certain electronic processes.
1. Hot objects
- When an object becomes sufficiently hot, it emits visible light.
- For example, a hot filament in an incandescent light bulb emits visible light.
2. Excited electrons
- Electrons in atoms can absorb energy and move to higher energy levels.
- When electrons move back to lower energy levels, they release energy.
- This energy can be emitted as visible light.
Uses
- Seeing: visible light enters the eyes and allows us to see objects.
- Photography: cameras detect visible light to produce images.
- Lighting: lamps and LEDs provide illumination.
- Optical communication: visible light can carry information.
Possible harm
Visible light is generally safe at normal intensities.
However:
- Very bright light can damage the retina.
- Looking directly at the Sun can cause permanent eye damage.
- Powerful lasers can damage the eyes and skin.
Ultraviolet radiation
How is ultraviolet radiation produced?
Ultraviolet radiation can be produced by very hot objects and by electrons releasing energy when they move between energy levels.
For example:
The Sun
The Sun is extremely hot and emits electromagnetic radiation, including ultraviolet radiation.
Electron transitions
- An atom absorbs energy.
- An electron moves to a higher energy level.
- The electron returns to a lower energy level.
- Energy is released as electromagnetic radiation.
- If the energy released is appropriate, ultraviolet radiation is produced.
Uses
- Security marking: UV light makes certain security marks visible.
- Fluorescent lamps: UV radiation causes a fluorescent coating to emit visible light.
- Sterilisation: UV radiation can kill microorganisms.
- Tanning: UV radiation stimulates the production of melanin in the skin.
Possible harm
- UV radiation can damage skin cells and DNA.
- It can cause sunburn.
- Excessive exposure increases the risk of skin cancer.
- It can damage the eyes.
- Long-term exposure can contribute to cataracts.
X-rays
How are X-rays produced?
X-rays are produced when high-speed electrons interact with a metal target.
For example, in an X-ray tube:
- A heated filament releases electrons.
- The electrons are accelerated through a large potential difference.
- The fast-moving electrons hit a metal target.
- Their kinetic energy is transferred to the target.
- X-rays are produced.
Uses
- Medical imaging: examining bones and internal structures.
- Airport security: examining the contents of luggage.
- CT scans: producing detailed images of the inside of the body.
- Industrial inspection: detecting cracks and defects inside materials.
Possible harm
X-rays are ionising radiation.
- They can ionise atoms in body tissues.
- They can damage DNA.
- They can cause mutations.
- They can increase the risk of cancer.
Gamma rays
How are gamma rays produced?
Gamma rays are produced by changes in the nucleus of an atom.
For example:
- An unstable nucleus undergoes radioactive decay.
- The nucleus may have excess energy.
- It releases this energy as gamma radiation.
- The nucleus moves to a lower-energy state.
Uses
- Cancer treatment: gamma radiation can destroy cancer cells.
- Sterilisation: used to kill microorganisms in medical equipment.
- Medical imaging: gamma rays emitted by radioactive tracers can be detected to produce images.
- Industrial inspection: used to inspect materials and detect defects.
Possible harm
Gamma rays are highly penetrating ionising radiation.
- They can ionise atoms in body tissues.
- They can damage DNA.
- They can cause mutations.
- They can increase the risk of cancer.
- At sufficiently high doses, they can kill cells and damage organs.