Physics- Electromagnetic Long Waves Flashcards
(12 cards)
What is the Electromagnetic Spectrum?
The Electromagnetic Spectrum is a group of waves that all travel at the speed of light (3 x 10 to power of eight m/s)
What are electromagnetic waves created by?
These waves are created by changes in electric and magnetic fields, therefore do not transfer energy using particles- they do it in a vacuum.
Are Electromagnetic waves Transverse or Longitudinal and what are their main characteristics?
They are all Transverse waves and they can all be reflected, refracted and diffracted.
What are Radio Waves used for and how?
Radio waves are used for communication purposes.
-Radio Waves are detected by aerials: the changing electromagnetic fields induce a small current in the aerial with a frequency that matches the signal- this is then interpreted by the receiver to produce a sound.
What is the advantage of using longer waves for Radio Waves?
The advantage of using longer waves include the ability to diffract around obstacles and carry almost no hazards.
How are Microwaves used when cooking food?
How else can they be used?
Microwaves can be absorbed by water: when cooking food, the waves reflect off the inside walls of the oven, penetrate the food to a depth of about 1cm, then excite the molecules in order to transfer energy through the food.
Microwaves can also be used for communications, in applications where radiowaves cannot work: they are more effective for communicating over longer distances by using satellites orbiting the earth.
What is Infrared Radiation and what can it be used for?
All objects emit Infrared Radiation (heat) to their surrounding, they emit more if they have a higher temperature.
These waves can be absorbed or emitted at diff rates by diff surfaces. Eg. Perfect Black bodies absorb and emit all infrared radiation.
Infrared Light can also be used for communication- remote controls have an Infrared LED that flashes in sequence to transmit signals to the device being controlled.
Data can also be sent through Optical Fibres using Infrared Light.
What is the Ionosphere?
The Ionosphere is a layer above the atmosphere, about 100km above the Earth’s surface.
What is the Ionosphere used for and why is this process necessary?
The Ionosphere is able to reflect Radio waves to enable them to pass around the Earth - known as Propagation and this process may need to be repeated several times.
This process is necessary since waves travel in a straight line, they cannot overcome the curvature of the Earth.
Which waves can penetrate the Ionosphere and what happens because of this?
Short wavelength microwaves (used by TV and mobile phone signals) cannot diffract around hills, and they can penetrate the ionosphere.
Their signals are repeated and redirected by satellites in space.
At surface level, the signals are passed between several masts, each covering a diff area.
What are Analogue signals used for?
Traditionally, analogue signals have been used for communication- the amplitude varies regularly
-However any interference or distortion is picked up by the receiver
What are digital signals used for?
Digital signals are a series of ‘on’ and ‘off’ binary states (0 and 1s) which are much easier to interpret when there is a little interference therefore a high quality transmission is received.
