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Which is the odd one out?. What are radio waves?. The broadcast of every radio and television programme involves the use of radio waves. Radio waves are the type of electromagnetic waves with the longest wavelengths. ultra- violet. micro- waves. radio waves. infrared. 1000 m. 1 m. 1 mm.
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What are radio waves? The broadcast of every radio and television programme involves the use of radio waves. Radio waves are the type of electromagnetic waves with the longest wavelengths. ultra- violet micro- waves radio waves infrared 1000m 1m 1mm 0.001mm wavelength of electromagnetic waves Radio waves have a wavelength greater than 30cm (the length of a standard ruler). Radio waves have many uses. How many can you think of?
How are radio waves produced? Radio waves are produced by passing an oscillating electric current through a long wire called an aerial. The frequency of the radio wave produced is the same as the frequency of the oscillating current. This allows radio waves of different wavelengths to be produced. These radio waves have slightly different properties and are used for different purposes.
What are radio waves used for? • Broadcasting Radio waves of different frequencies are used to broadcast radio and television. • Communications Several types of radio waves are used for communications. • Radio control • Radio waves can be used to send signals • to control model cars, planes and boats. • Radio frequency identification This identification system involves tagging an object, animal or person with a microchip that responds to specific radio frequencies. It can be used to identify pets and keyless locks on doors.
Can radio waves travel through walls? Radio waves are not absorbed strongly by walls, which is why radio (and television) signals can be received indoors. Tall objects, like buildings and hills, can prevent radio waves travelling directly from a transmitter, but this is not always a problem. In some areas, the reflection of waves off other buildings or hills can actually lead to improved radio reception.
How do radios work in hilly areas? In hilly areas there may not be a clear path between the transmitter and the radio, so how can a signal be received?
What is diffraction? Diffraction is a property of all waves, which can be shown by water waves in a ripple tank. Here, the waves travel along until they reach a gap. The width of the gap is similar to the wavelength of the waves. The waves pass through the gap and spread out. This is diffraction. So, when radio waves travel past an obstacle or through a narrow gap, they bend or spread out due to diffraction.
How does wavelength affect diffraction? The amount of diffraction depends on how the wavelength compares with the size of the gap. What happens if the wavelength is much smaller than the width of the gap? In this case, only the edges of the wave front are diffracted. The amount of diffraction depends on wavelength. The longer the wavelength, the greater the diffraction.
When have I experienced diffraction? How can the teacher hear the band but not see them? Sound waves have a wavelength similar in size to the width of the doorway and so are diffracted as they pass through. Light waves have a much shorter wavelength than sound waves and so are not diffracted by the doorway. This means the band can be heard but not seen by the teacher in the corridor.
What are microwaves? Every mobile phone conversation involves the transmission of microwave signals. Microwaves are a form of electromagnetic radiation. They are very short-wavelength radio waves. ultra- violet micro- waves radio waves infrared 1000m 1m 1mm 0.001mm wavelength of electromagnetic waves The wavelength of microwaves ranges from 30cm (the length of a standard ruler) to 1mm (about the size of a full stop). Microwaves have many uses. How many can you think of?
How are microwaves produced? Microwaves with different wavelengths have slightly different properties and uses. They are also produced in different ways. Long-wavelength microwaves are produced by aerials in a similar way to other radio waves. These types of microwaves are used for communications. Short-wavelength microwaves are produced using a device called a magnetron. These types of microwaves are used by microwave ovens and radarequipment.
How are microwaves used? • Heating food A microwave oven uses microwaves to generate heat and warm food. • Communications Microwaves are used to send communications signals to and from satellites. They also carry signals for mobile phones, wireless computer networks and personal digital assistants. • Radar (radio detection and ranging) Radar equipment bounces microwaves off moving objects to detect them. • Astronomy Large microwave receivers called radiotele- scopes study microwaves emitted from space.
Downpour (>16mm/hour) Very heavy (8-16mm/hour) Heavy (4-8mm/hour) Moderate (2-4mm/hour) Moderate (1-2mm/hour) Slight (0.5-1mm/hour) Very slight (0.5mm/hour) How can microwaves monitor rainfall? Weather radar uses microwaves to scan for raindrops in the atmosphere. The radar sends out pulses of microwaves, which are reflected by raindrops. By listening to the reflected pulses, the radar works out the rain’s location and intensity. In general, the more intense the reflected signals, the higher the rain intensity. The distance of the rain is determined from the time it takes for the microwaves to travel to and from the raindrops. Radar images displayed in television weather reports use a colour scale to represent the different intensities of rainfall.
How does my mobile phone work? Mobile phone networks divide areas into smaller areas called “cells”. There is a base station at the centre of each cell. incoming signal Your mobile phone is a two-way radio that uses microwaves to communicate with the nearest base station. Different frequencies are used for the incoming and outgoing signals. This allows you to listen and talk at the same time. outgoing signal When you move from one cell to another, the network detects a weakening signal and hands over to another base stationwhich is detecting a stronger signal from your phone.
What affects my mobile phone reception? Mobile phone reception is affected by a number of factors. Microwaves lose intensity as they travel, so the distance between the phone mast and the mobile phone is important. Another factor is tall buildings, which can create pockets with no reception. To overcome this, mobile phone companies use lots of low power transmitters to fill in the gaps caused by the buildings.
Why limit the use of mobile phones? Some people are concerned about mobile phone use because the handsets emit microwaves close to the body. The government recommends that users take reasonable steps to limit their exposure to the microwaves by following the ALARA principle. This involves the following precautions: As Low As Reasonably Achievable • Using a hands free kit or shield. • Using a phone which emits less radiation. • Not talking on a mobile for a long time. • Under 16s only using mobiles when essential.
Is hands free going to make a difference? Rachel wanted to investigate the advice that placing the aerial of a mobile phone further from the head would reduce the amount of radiation being absorbed by the brain. This apparatus was available for her microwave investigation. What is the independent variable? The distance between the transmitter and the receiver. What is the dependent variable? The intensity of microwave radiation detected at the receiver. microwave transmitter microwave receiver To collect valid results,Rachel chose a range of distances (0,10,20,30,40and50cm) that a mobile phone may be fromthe head when it is used with or without a hands-free kit.
Could hands-free make a difference? The results of the microwave experiment can be plotted to see if there is a relationship between intensity of the radiation and distance from the source. Rachel’s results show that as the distance increases the intensity of the microwave radiation decreases. x intensity / A x x x x x distance / cm How does this relate to safer use of a mobile phone? The results suggest that moving the mobile phone away from the head, even a few centimetres, could reduce the intensity of radiation reaching the head.
Can mobile phone masts harm us? There are concerns that the microwave radiation emitted by mobile phone masts may present a threat to health. One reason for this concern is that a mobile phone mast continually emits microwave radiation. A mobile phone only emits radiation when in use. Mobile phone masts are also higher power than phones. However, people are less likely to be right beside a mobile phone mast and microwave intensity is reduced with distance. You will probably receive a higher dose of microwaves from your phone than from a mast.
aerial – A device used to transmit or receive radio waves. • ALARA –The “As Low As Reasonably Achievable” principle, which limits exposure to electromagnetic waves. • base station – Equipment at the centre of a mobile phone cell, which transmits and receives mobile phone signals. • diffraction –The spreading or bending of waves as they travel through a narrow gap or past an obstacle. • magnetron –The electronic device that generates microwaves and is used in radar and microwave ovens. • microwaves –Electromagnetic waves with wavelengths from 30cm to 1mm. They are short-wavelength radio waves. • radar –Short for “radio detection and ranging”, a system that bounces microwaves off moving objects to detect them. • radio waves – Electromagnetic waves the longest wavelengths. Glossary
