Electro-Magnetic Radiation. Intro to Electro Magnetic Waves ( or electromagnetic radiation) (or EMR).
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Changing Magnetic field (or acceleration of a magnetic object) => Electric Field
Changing Electric field ( or acceleration of a charged object) => Magnetic field
We know that a changing electric field creates
magnetic field. We also know that a changing
magnetic field will create an electric field.
What does this mean?
It means that an alternating magnetic field OR electric field will create self propagating electromagnetic waves!
Wave length=the distance over which the wave completes a cycle.
Frequency= the number of wave lengths which pass a point per second.
This gives a relationship between frequency and wave length:
Maxwell’s equations however, restrict the value of velocity to a single value
called C, which is equal to 3*10^8 m/s
You have all heard the word photon right?
It refers to the smallest piece of energy in
radiation form that can be emitted or absorbed
at a specific frequency, and strangely enough
Photons behave like particles, with no mass, a
Constant speed of C. The energy of a photon is
proportional to its frequency. In fact everything
Can be described as a wave. Google wave particle
duality if you get the chance.
However, we are going focus on the EMR generated by oscillations of charged particles because… you are already familiar with charged particles!
They are in the stinking names on the spectrum….
the heat you feel from fires, sun burns, MRI’s, Night vision… your ideas…
Sterilization of produce (gamma/UV rays), determining the age of the universe (no big deal…), chemo-therapy, setting clocks, precise measurement
We are all familiar with the particle model of
matter right? Right. In case you are not,
everything that has mass is composed of, or is a
small charged particle. We also know that these
Particles are in constant motion (assuming that
the object is not at absolute zero temperature.
What does this mean… hmmm…..
-Thermal radiation is the electromagnetic radiation emitted by matter, because of all the oscillating charged particles that are its components.
Temperature=Measurement of the averagekinetic energy of the particles/molecules in an object.
Heat=A form of energy transfer by changing kinetic energy of the particles of objects.
Absolute zero= 0 degrees Kelvin
The Stefan-Boltzmann Law has some pretty cool applications. It gives us a relation between the total energy in electromagnetic radiation emitted per unit time, the surface temperature of an object in Kelvin, its surface area, the boltzmann constant and the objects emissivity.
How could we then measure the temperature of an object? What would we need?
Does that seem right? If not what are we missing?
I know you all believe that this EMR stuff exists,
but I believe we take the application of our
knowledge of EMR for granted. I hope this quick
Demo will leave you with an appreciation of
sciences ability to translate information from a
medium outside of human sensory perception
into a usable, accessible form.
We have a few minutes for you to ask questions
that came up during the lecture, The UBC
Physics Program or university in general!