topic 6 continued Flashcards
how do EM waves transfer energy
they transfer energy from the source of the waves to an absorber
how do microwaves transfer energy
from the source which is the microwave to the absorber which is the food
the frequency … from radio waves to the gamma rays
increases
the wavelength … from radio waves to the gamma rays
decreases
what can EM waves travel through
a vacuum (space)
all EM waves travel at the same … in a vacuum
speed
at what speed do EM waves travel in a vacuum
3 x 10^ 8 m/s
what happens when EM waves are generated or absorbed
changes takes place in atoms or in the nuclei of atoms
how can an em wave be generated
by a change to the nucleus
how can radio waves be produced
when electrons oscillate (move backwards and towards)in electric circuits
give an example of how radio waves can be absorbed
by an electrical circuit in an aerial- this causes the electrons in the circuit to oscillate
what type of current can radio waves create and what does it have the same of
alternating current with the same frequency as the radio waves
why are radio waves used in TVs and radios
because they can travel long distances before being absorbed e.g. by buildings and trees
what can radio waves do in the atmosphere
they can reflect off a layer of charged particles in the atmosphere- this allows us to send radio waves at very long distances around the earth
why are microwaves used in communication with satellites
because microwaves can pass through the earths atmosphere without being reflected or refracted
why is infra-red used to heat objects etc
because the energy of the infra-red is easily absorbed by the surface of the objects
What can EM waves do that leads to refraction
They travel at different speeds in different materials
EM waves vary in wavelength from …
10^-5 - 10^4
Wavelength of radiowaves
1m - 10^4
Microwaves wavelength
10^-2m
Infra-red wavelength
10^-
Visible light wavelength
10^-7m
Ultraviolet wavelength
10^-*8m
X-rays wavelength
10-10 m
Gamma rays wavelength
10^-15m
Why is there a large range of frequencies in the EM spectrum
Because the EM waves are generated by a variety of changes in atoms and their nuclei
Changes in the nucleus of an atom creates …
Gamma rays
What bit of the spectrum can our eyes detect
Visible loght
What does it mean is a wave is ABSORBED by the second material
The wave transfers energy to the materials energy stores. Often the energy is transferred to a thermal energy store which leads to HEATING
What does it mean if the wave is TRANSMITTED through the second material
The wave carries on travelling through the new material which often leads to refraction
What does it mean if the wave is REFLECTED
This is where the incoming ray is neither ABSORBED or TRANSMITTED but instead is sent back away from the second material
If the wave hits the boundary at an angle it …
Changes direction- it is refracted
How much a wavs is refracted depends on what
How much the wave speeds up or slows down which depends on the density of the 2 materials
When will a wave speed up
- when its travelling along the normal
- when the wave bends AWAY from the normal
When will a wave slow down
-if the wave BENDS towards the normal
How can long wavelength radio-waves travel at long distances
Because long wavelengths diffract around the curve surface of the earth
How can short wavelength radio signals be received at long distances by a TRANSMITTER
Because they are reflected from the ionosphere- an electrically charged layer in the earths upper atmosphere
What is fluorescence a property of
Certain chemicals where ultra-violet radiation is absorbed and then visible light is emitted
What is period
The total time taken for a full cycle of the wave
