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Electromagnetic Spectrum presentation notes
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Stonebridge electromagnetic spectrum presentation natural science pathway
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Hello so today I’m going to be broadly looking at the electromagneticspectrum. within this presentation I will be looking at the principles and
properties of types of electromagnetic waves, properties of microwaves and
infrared the uses and hazards of x-rays within a medical application and
within the context of crime scene investigation. I’ll be comparing and
contrasting the properties of visible and I’ve light. I’ll be explaining some
applications of visible and UV light and I’ll be explaining the biohazards of UV
in infrared radiation and their main effects.
Principles and properties of types of electromagnetic waves. The
electromagnetic is made up of waves.
What is an electromagnetic wave? These travel at a speed of 300 million
meters per second. They have a range of wavelengths and frequencies at
different amplitudes.
The human eye can detect a band of these wavelengths and this is known as
the spectrum of visible light which we see as colours. What we cannot see
begins with the infrared and ultraviolet.
This here is the spectrum. Here we’ve got visible light, then infrared and
then ultraviolet. Although we cannot see these, we can still experience their
effects we feel the heat of infrared radiation coming off of hot objects and we
know the damage that ultraviolet radiation can cause our skin if we’re
exposed to too much sun.
This diagram here shows us more about the applications of the
electromagnetic spectrum. Beyond the two wavelengths I’ve just discussed
we have longer wavelengths with lower frequencies down at this end such as
microwaves, radio waves and tv signals used for communication. Then at
this end we have shorter wavelengths but higher frequencies such as x-rays
and gamma rays which are more penetrating and are used in medicine and
industry.
This is what an electromagnetic wave will look like, electric and magnetic. So
here we’ve got the electric field demonstrated in blue and magnetic field
demonstrated in red. They will travel together. The two fields oscillate at a
right angle to each other and move through a vacuum at the speed of 300
million meters per second. This is the shape of a transverse wave and within
this we have crest through amplitude wavelength also we cannot see
frequency. This one here is the distance between peaks and is measured in
meters represented by this symbol here which is the Greek letter lambda.
Secondly, we have amplitude which we can see just here, and this is the
wave peak height from the baseline, and this is the power of a wave. For
example, when you turn up the volume of your music and amplitude of the
wave and will increase within the electromagnetic spectrum it’s a measure of
intensity. For example, if you were to look at light it would be its brightness.
Not shown on this diagram we have frequency which is the number of peaks
, per second and this is measured in cycles and its measurement is hertz. One
Bert is one cycle per second so when we talk of a cycle, we are talking about
the wave moving from the centre, which is the base, up to the top of its peak
down to the bottom of its trough and back up to the centre line and that will
be one cycle.
If we have a look at wavelengths, we’re always looking at frequency and
wavelength and the two are said to be inversely proportional so this means
that as one value goes up another value will go down. A low frequency gives
us a long wavelength and a high frequency will give us a short wavelength.
Here we have what is known as a wave equation. These measurements are
related, and the equation calculates the waves velocity. The velocity is the
frequency by the wavelength the velocity or wave speed is represented by
“v” which is this here and it is measured in metres per second and we can
change the equation to find out different things. Velocity is frequency by
wavelength but if we wanted to find out wavelength for example, this would-
be velocity over frequency.
Properties over microwave and infrared.
So infrared, occurs at frequencies above those of microwaves and just below
those of red Vida or light hence the name. Invisible to the eye but it can be
felt as heat and is emitted by all objects including humans, fires and the sun.
Infrared has its own range of wavelengths. The shorter near infrared waves
close to visible light don’t emit any detectable heat and this is what’s
discharged from a tv remove to change the channel. The longer waves closer
to microwaves can be as intense heat such as the heat from the sunlight or
from a fire.
This is what we use for thermal imaging. Infrared sensing, as spoken about
all objects emit heat and this can be detected by electronic sensors such as
those used in night vision goggles the image here, and infrared cameras, the
image here. Active infrared sensors consist of two elements, infrared source
and infra detector. The energy emitted by the infrared source is reflected by
an object unfold on the infrared detector. So, if you look at a bolometer,
which is a basic of this sort of detector. It consists of a telescope with a
temperature sensitive resistor or thermistor at its focal point and I’d a body
comes into the instrument’s field of view the heat causes a detectable
change in the voltage across the thermometer. There is a similar process for
night vision goggles but a little bit more sophisticated.
Microwaves. They fall in the range of the electromagnetic spectrum between
radio here and infrared here. Microwaves are used in radar communication
and for heating in a microwave oven, which we most commonly known, they
will heat the food from the inside out however, I will be looking at
microwaves within communication.
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