Flashcards in P1 6 Electromagnetic Waves Deck (39):
What are electromagnetic waves?
Electric and magnetic disturbances that transfer energy from one place to another (can travel through a vacuum)
What does the energy the wave transfers depend on?
What is the order of the electromagnetic spectrum?
What speed do all electromagnetic waves travel at?
300 million m/s
What is the formula for calculating the speed of a wave?
Speed = frequency x wavelength
What happens to the frequency as the wavelength shortens?
How does frequency link with energy?
The higher frequency the more energy.
What is a kilohertz and megahertz equal to?
What is light from ordinary lamps and the sun known as?
Why is it known as white light?
It has all the colours of the visible spectrum
Which has a longer wavelength?red or violet?
What is done to light in a film camera?
Light is focused by the camera lens onto a light-sensitive film.
The film is then developed to see the objects that have been photographed.
What is done to light in a digital camera?
Light is focussed by the lens on to a sensor which has lots of tiny light sensitive cells called pics. These are dots in images.
The image is seen on a small screen at the back of the camera.
When the photograph is taken, it is stored electronically on a memory card.
What do all objects emit?
Infra red radiation
Infra red radiation is absorbed by the skin. What can it cause?
Damages and kills skin cells because they get heated.
State some infra red devices and why they use infra red.
Optical fibres in communications systems: it is absorbed less than light in the glass fibres
Remote control: transmit signals
Infrared scanners: to detect 'hot spots'
Infrared cameras: to see people and animals in the dark
State some microwave devices and why they use microwaves.
Communications: can pass through atmosphere
Mobile phone signals and beam signals: doesnt diffract much
Heating food: agitates water molecules
State some radiowave devices and why they use radiowaves.
Connection from computers to devices: have a wide frequency range
Give an example of a use for each wave.
Radio - tv signals
Microwaves - heating food
Infrared - remote controls
Visible light - cameras
Ultraviolet - detect forgery, kill pathogens
X-ray - security
Gamma - sterilise, kills cancerous cells
The shorter the wavelength of the wave?
The more information they carry
The shorter their range
The less they diffract and spread out
What are microwaves used for in communications?
Satellite TV and TV links and broadcasting because they can they can travel between satellites in space and the ground and spread less so signal isn't weakened as much.
What are microwaves less than a metre used for?
Tv broadcasting and masts as they carry more information than longer ones.
What are radiowaves from a metre to 100m used for?
Local radio stations and emergency services as the range is limited to the area around its transmitter.
What are radio waves more than 100m used for?
National and international radio stations as they have a much longer range.
How does a mobile phone signal work?
It sends a radio signal which is picked up by the nearest phone Nast and is sent through the phone network to the other phone. The returning is the signal goes back through the network to the mast neatest to you.
What are optical fibres?
Thin glass fibres.
What are optical fibres used for?
Transmit signals by light and infrared.
How do optical fibres work?
The light cannot escape from the fibre so is reflected back from the surface into the fibre.
Why are optical fibre communications better than radio and microwaves?
They carry much more information
They are more secure as all signals stay inside
How do radio communications work?
The waves are emitted from an aerial when we apply an alternating voltage. These frequencies are the same. When these waves pass across a receiver aerial they cause a tiny alternating voltage in the aerial. These frequencies are the same. The alternating voltages cause the loudspeaker to send out wves.
Explain the Doppler effect.
As the object making the sound moves towards a person, a higher frequency is heard due to the waves being squashed together and creating a shorter wavelength.
As it moves away a lower frequency is created as they are further apart and longer wavelength.
What does a spectrum of a star consist of?
Dark lines called absorption lines. This is where light is absorbed
What does red shift and blue shift tell us?
Read shift means that the lines are moving towards the red end. It means the wave length is stretched and is moving away from us. The faster a galaxy or star is moving the bigger the shift. Vise versa for blue shift.
What is the Big Bang theory?
A theory which explains the beginning of the universe.
How did the Big Bang start?
From a massive explosion from a very small initial point.
What three things were created in the big bang?
What has been happening ever since the Big Bang?
The universe has been expanding.
What other thing is being created by the Big Bang?
Cosmic microwave background radiation