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Electro-Magnetic Radiation

Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

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Page 1: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Electro-Magnetic Radiation

Page 2: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Intro to Electro Magnetic Waves(or electromagnetic radiation)

(or EMR)

• Electro-Magnetic Radiation is an interesting subject in physics in part due to the fact that we interact with EMR (electromagnetic Radiation) or technology that makes use of our understanding of electromagnetic Radiation to enhance our lives.

• EMR is also amazing because it is responsible for one of the integral senses that makes up the human experience, sight! Our sense of sight, and the beautiful multi-colored world we live in is based on our bodies ability to make sense of a small section of EMR.

• The amount of information contained in the electromagnetic waves/radiation that surrounds us, is astounding, and by studying it we discovered things completely out side of human sensory perception.

Page 3: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Electromagnetic Waves*In a Vacuum…

Maxwell-Faraday Equation:

Changing Magnetic field (or acceleration of a magnetic object) => Electric Field

Page 4: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Electromagnetic WavesContinued…

Maxwell-Ampere’s equation:*approximate form

Changing Electric field ( or acceleration of a charged object) => Magnetic field

Page 5: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Now what do we know?

We know that a changing electric field createsmagnetic field. We also know that a changingmagnetic 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!

Page 6: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

How does this wave behave?

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:Velocity=frequency*wavelength Maxwell’s equations however, restrict the value of velocity to a single valuecalled C, which is equal to 3*10^8 m/s

Page 7: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Electromagnetic Spectrum

Page 8: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

The Particle Model of Light

You have all heard the word photon right? It refers to the smallest piece of energy inradiation form that can be emitted or absorbedat a specific frequency, and strangely enoughPhotons behave like particles, with no mass, aConstant speed of C. The energy of a photon isproportional to its frequency. In fact everythingCan be described as a wave. Google wave particleduality if you get the chance.

Page 9: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

How is EMR generated?

• Electro/magnetic waves/radiation can be emitted by oscillating charges.

• Quantum and Nuclear processes (responsible for most of the high energy radiation in our universe) *missing mass problems and discrete energy levelsHowever, we are going focus on the EMR generated by oscillations of charged particles because… you are already familiar with charged particles!

Page 10: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Where do we come into contact with EMR?

• No brainers!

• Think a littler harder…

• Ok impress me…

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

Page 11: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Zooming in on Thermal Radiation

We are all familiar with the particle model ofmatter right? Right. In case you are not,everything that has mass is composed of, or is asmall charged particle. We also know that theseParticles are in constant motion (assuming thatthe object is not at absolute zero temperature.

What does this mean… hmmm…..

Page 12: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

ALL MATTER EMITS RADIATION!*and we call it thermal radiation

-Thermal radiation is the electromagnetic radiation emitted by matter, because of all the oscillating charged particles that are its components.

Page 13: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Some review…

Temperature=Measurement of the average kinetic 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 Kelvin= Celcious+273

Page 14: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

So back to thermal Radiation…

• We know that temperature is a measurement of how vigorously a particle oscillates… therefore we should see higher quantities of and greater frequencies of electromagnetic radiation.

• So it should be possible to relate temperature to the amount and frequency of radiation emitted by an object… and luckily somebody else did all the work for us!

Page 15: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Stefan-Boltzmann Law

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?

Page 16: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Black Body Spectrum

Page 17: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

A few minutes of thinking…

• You are a an engineer working for me If I gave you a sensor that can get a reading for temperature and a computer that can take that reading and inform other pieces of machinery what to do, can you think of some possible applications of our understanding of EMR?

Page 18: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Quick Problem

• Lets calculate the energy loss do to radiation of a human body. (oh yeah! IR sensors at border crossings are used to check for human trafficking)

• P=A*e*(boltz)*T^4 approximate!

Page 19: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

What Google says…

• Google says approximate surface area is 1.8m^2

• Google says an average temperature for the surface of a human body is 306K.

• Google says the emissivity of human flesh is .97• Therefore, Google says that P=870W

Does that seem right? If not what are we missing?

Page 20: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

My Demonstration

I know you all believe that this EMR stuff exists,but I believe we take the application of ourknowledge of EMR for granted. I hope this quickDemo will leave you with an appreciation ofsciences ability to translate information from amedium outside of human sensory perceptioninto a usable, accessible form.

Page 21: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject
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Page 23: Electro-Magnetic Radiation. Intro to Electro Magnetic Waves (or electromagnetic radiation) (or EMR) Electro-Magnetic Radiation is an interesting subject

Questions?

We have a few minutes for you to ask questionsthat came up during the lecture, The UBCPhysics Program or university in general!