24 total
By the end of this topic, you should be able to:
Core:
Supplement: 6. Know that the speed of electromagnetic waves in a vacuum is 3.0 × 10⁸ m/s and is approximately the same in air 7. Know that many important systems of communications rely on electromagnetic radiation 8. Know the difference between a digital and analogue signal 9. Know that a sound can be transmitted as a digital or analogue signal 10. Explain the benefits of digital signalling
The electromagnetic spectrum is a range of different types of waves arranged in order. These waves are all around us, even though we can only see a small part of them with our eyes. The spectrum includes everything from radio waves (which carry radio signals) to gamma rays (used in cancer treatment).
All electromagnetic waves:
The electromagnetic spectrum has seven main regions. They are always arranged in the same order, either from longest to shortest wavelength, or from lowest to highest frequency.
Order from longest wavelength to shortest wavelength:
Order from lowest frequency to highest frequency:
Key relationship to remember:
A helpful way to remember the order is the mnemonic: Raging Martians Invaded Venus Using X-ray Guns.
Visible light is just one small part of the electromagnetic spectrum. It's the only part that human eyes can detect. White light (like sunlight) is actually made up of different colours.
When white light passes through a glass prism, it splits up into different colours. This process is called dispersion. The colours appear in this order: Red, Orange, Yellow, Green, Blue, Indigo, Violet (you can remember this as ROYGBIV).
Why do the colours separate?
All electromagnetic waves travel at the same high speed in a vacuum (empty space). This is true whether the wave is a radio wave, visible light, or a gamma ray.
Supplement only: The exact speed of electromagnetic waves in a vacuum is 3.0 × 10⁸ m/s (which is 300,000,000 metres per second). This is often called the "speed of light." The speed is approximately the same in air.
Each region of the electromagnetic spectrum has specific uses based on its properties.
Radio waves have the longest wavelength and lowest frequency in the electromagnetic spectrum.
Uses:
Microwaves have shorter wavelengths than radio waves but longer than infrared.
Uses:
Infrared is sometimes called "heat rays" because warm objects give off infrared radiation.
Uses:
Visible light is the only part of the spectrum humans can see with their eyes.
Uses:
Ultraviolet (UV) waves have higher frequency than visible light. The Sun produces UV radiation.
Uses:
Fluorescence is when certain materials absorb UV light and then re-emit it as visible light, making them glow.
X-rays have very short wavelengths and high frequencies. They can pass through soft materials but are absorbed by dense materials.
Uses:
Gamma rays have the shortest wavelength and highest frequency in the electromagnetic spectrum. They are the most energetic waves.
Uses:
While electromagnetic waves are useful, excessive exposure (too much exposure) to some types can be harmful to people.
Harm: Microwaves can be absorbed by water molecules in the body. Since the human body contains a lot of water, high-intensity microwaves can cause internal heating of body cells, which can damage tissues inside the body.
Safety note: The microwaves used for mobile phones emit very small amounts of energy and are not known to cause harm. Microwave ovens emit large amounts of energy, but the metal walls and metal grid in the door prevent the microwaves from escaping.
Harm: Infrared radiation is heat. Excessive exposure to infrared can cause skin burns, similar to touching something very hot.
Harm: Ultraviolet (UV) radiation carries more energy than visible light. Excessive exposure can:
Protection: Sunscreen absorbs UV light to protect skin. Good quality sunglasses absorb UV light to protect eyes.
Harm: X-rays and gamma rays are the most energetic and dangerous types of electromagnetic radiation. They can:
These rays are called ionising radiation because they have enough energy to remove electrons from atoms, creating ions. This is what causes the cell damage.
Safety note: Medical professionals use X-rays carefully, taking the minimum number of images needed and using lead shields to protect parts of the body not being scanned.
Artificial satellites are man-made objects that orbit (go around) the Earth in space. Many communication systems use satellites to send signals around the world.
Microwaves are mainly used for satellite communication because:
Low orbit satellites orbit at about 200 km above the Earth's surface. This is relatively close to Earth.
Uses:
Advantages:
Disadvantages:
A special type of low orbit satellite is a polar orbit satellite, which orbits over the North and South poles.
Geostationary satellites orbit above the Earth's equator at a height of about 36,000 km. They take exactly 24 hours to complete one orbit, which matches the Earth's rotation. This means they stay in the same position above the Earth.
Uses:
Advantages:
Disadvantages:
Many modern communication systems rely on electromagnetic radiation. The type of radiation used depends on what properties are needed.
Mobile phones (cell phones) and wireless internet use microwaves.
Why microwaves?
Mobile phone networks use a system of transmitter masts. Each mast relays the signal to the next one, creating coverage across large areas.
Bluetooth is a technology that allows devices (like phones, speakers, and headphones) to communicate wirelessly over short distances.
Why radio waves?
Optical fibres are thin, flexible glass cables that carry signals using light.
Uses:
Why visible light or infrared?
Optical fibres are faster and can carry more information than traditional copper cables.
Information (like sound, pictures, or data) can be transmitted as either digital or analogue signals.
An analogue signal varies continuously. This means it can take any value at any time. The signal changes smoothly from one value to another.
Example: When you speak, your voice creates sound waves that continuously change in pitch and volume. These are analogue waves.
Characteristics:
A digital signal can only take one of two discrete (separate) states. These are usually called:
Characteristics:
Sound can be transmitted as either a digital or analogue signal.
Process:
Digital signals have several advantages over analogue signals:
Digital signals can transmit information faster than analogue signals. This means more data can be sent in the same amount of time.
Why: Digital signals use a simple binary code (1s and 0s), which can be processed and transmitted very quickly.
Digital signals can travel longer distances without losing quality.
Signal regeneration means that devices along the transmission path can recreate the signal perfectly. Because a digital signal only has two states (1 or 0), it's easy to identify what the signal should be, even if some noise has been added.
How regeneration works:
With analogue signals, any noise added during transmission stays in the signal and gets worse over distance. With digital signals, the noise is removed through regeneration.
Digital signals experience less interference than analogue signals because the signal can be checked and cleaned up at each regeneration point.
Extra data can be added to digital signals that allow receiving devices to check for and correct errors.
Sign in to view full notes