3.3 Electromagnetic spectrum
Main Regions of the Electromagnetic Spectrum
The electromagnetic spectrum is arranged in order of:
- Frequency: Lowest to highest → Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma rays.
- Wavelength: Longest to shortest → Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma rays.
Radio waves have the lowest frequencies and longest wavelengths, while gamma waves have the highest frequencies and shortest wavelengths. All of these waves travel at the same speed in free space, which is the speed of light or about 300,000,000 m/s or 3.0 × 10⁸ m/s
Uses of Different Regions of the Electromagnetic Spectrum
- Radio waves: These have the longest wavelengths and the lowest frequencies. Used for radio and TV broadcasts, astronomy, and RFID (Radio Frequency Identification).
- Microwaves: Shorter wavelengths than radio waves, Used in satellite TV, mobile phones, and microwave ovens.
- Infrared: This is heat energy. Infrared waves are felt as warmth and are used in electric grills, short range communications such as remote controls, intruder alarms, thermal imaging, and optical fibers.
- Visible light: This is the only part of the spectrum we can see with our eyes. Allows us to see, is used in photography, and for general lighting.
- Ultraviolet (UV): Invisible to our eyes, UV is found in sunlight. Used for security marking, detecting fake banknotes, and sterilising water.
- X-rays: These waves can pass through most body tissues but not through bones. Used in medical scans and security scanners.
- Gamma rays: The shortest wavelength and highest energy. Used to sterilise food and medical equipment, and in the detection and treatment of cancer.
Harmful Effects of Electromagnetic Radiation
| Wave | Safety issues | Safety precautions |
|---|---|---|
| Microwaves | Microwaves can cause internal heating of body tissues. Exposure to high levels can result in painful burns. | 1. Minimize time spent near sources of high microwave radiation. 2. Maximize distance from microwave sources. 3. Use protective barriers when necessary (e.g., microwave ovens are shielded). |
| Infrared Radiation | Infrared radiation is felt as heat, and excessive exposure can cause skin burns. | 1. Avoid direct exposure to strong infrared sources (like heaters or the sun). 2. Wear insulating gloves or protective clothing if handling infrared sources. |
| Ultraviolet (UV) Radiation | UV rays can damage surface cells and eyes. This can lead to skin burns, eye conditions like cataracts, and skin cancer. | 1. Limit exposure to sunlight (especially midday). 2. Wear sunscreen and protective clothing. 3. Use UV-blocking sunglasses to protect the eyes. |
| X-rays | X-rays can damage cells, causing mutations, which may lead to cancer. Prolonged exposure can also cause skin reddening and hair loss. This is why protective measures are taken when frequent X-rays are needed. | 1. Minimize exposure time to X-rays. 2. Maximize distance from the X-ray source. 3. Use protective shielding, such as lead aprons, to block radiation. |
| Gamma rays | Gamma rays are highly penetrating and can pass through bones and tissues. They can destroy living cells, cause gene mutations, and increase the risk of cancer. | 1. Limit exposure to gamma radiation. 2. Maximize distance from the gamma source. 3. Use lead or thick concrete as shielding to protect from gamma radiation. |
Additional Notes on Safety Precautions:
- Infrared: Found in devices like heaters and remote controls. While it is not as dangerous as UV, prolonged exposure to strong infrared sources, like industrial heaters, can cause burns.
- Ultraviolet (UV): UV rays from the sun are the most common source of exposure. Overexposure can cause sunburn and long-term issues like skin cancer, so sunscreen and protective eyewear are vital for protection.
Communication with Artificial Satellites
Satellites and Communication
- Satellites are objects that orbit the Earth. The Moon is Earth’s natural satellite, while there are also many artificial satellites used for communication.
- Most artificial satellites use microwaves to transmit information because microwaves can travel long distances and pass through the Earth’s atmosphere.
Types of Satellite Orbits
- Geostationary Satellites
- These satellites orbit the Earth at the same rate the Earth rotates, so they remain above the same point on the Earth’s surface.
- They are located 35,000 km above the Earth’s surface, positioned above the Equator.
- Geostationary satellites are powerful and can transmit large amounts of data, making them suitable for services like satellite television and some satellite phones.
- Because the waves travel such long distances to the satellite and back, there is a slight delay in the transmission, making real-time conversations harder.
- Low Earth Orbit (LEO) Satellites
- These satellites are much closer to the Earth’s surface, at distances as low as 2,000 km.
- LEO satellites orbit the Earth quickly, completing an orbit in as little as two hours.
- There is no delay in communication, making them ideal for satellite phones.
- However, they cover a small area of the Earth’s surface, so many LEO satellites are needed to provide full coverage.
- LEO satellites cannot transmit data as fast as geostationary satellites, so they are not suitable for television transmission.
Supplement
Speed of Electromagnetic Waves in a Vacuum
- Electromagnetic waves travel at 3.0 × 10⁸ m/s in a vacuum, and at almost the same speed in air.
Electromagnetic Radiation in Communication Systems
Many of the technologies we use every day rely on electromagnetic waves for communication:
- Mobile phones and wireless internet use microwaves. Microwaves are chosen because they can pass through walls, and only need a small aerial (antenna) for sending and receiving signals.
- Bluetooth uses low-energy radio waves or microwaves. These waves can also pass through walls, but the signal weakens when they do, so Bluetooth is usually used for short distances, like connecting headphones to a phone.
- Optical fibres use visible light or infrared to carry information. These are very useful for cable TV and high-speed internet because light and infrared waves can travel quickly through glass, which is transparent to these waves. They also carry a lot of data.
Digital vs. Analogue Signals
- Digital signals are made of numbers (0s and 1s) and represent information in a clear-cut way.
- Analogue signals are continuous and can take any value over a range. This means they can be easily affected by noise or interference.
Sound can be sent as digital signals (where it is converted into 0s and 1s) or as analogue signals (where it is transmitted as continuous waves).
Benefits of Digital Signaling
Digital signals have several advantages over analogue signals:
- Faster data transmission: Digital signals can carry a lot of information in a short time.
- Increased range: Digital signals can travel long distances without losing quality because they can be easily regenerated (or refreshed) to stay clear.
- Reduced interference: Digital signals are less affected by noise or distortion compared to analogue signals, which makes communication more reliable.