GENERAL PHYSICS 2

MAXWELL’S SYNTHESIS OF ELECTRICITY, MAGNETISM, AND OPTICS

EM WAVES AND LIGHT
MELC’s Relate the properties of EM wave (wavelength, frequency, speed) and the properties of
vacuum and optical medium (permittivity, permeability, and index of refraction)
STEM_GP12OPTIVb-12
Introduction Light is commonly defined as electromagnetic wave but what is an electromagnetic wave and
with also what is electric and magnetic about light?
preliminaries
A pleasant day to everyone, get yourselves ready. Pick up a pen, paper and your module in
General Physics 2.

You are with Teacher Kaye Lim and welcome to my class where everything’s KAYE OK in
KAYE’S VIRTUAL CLASSROOM.
Review of Past Before we proceed to our new lesson, let us have some review of our previous discussion.
Lesson
Identify what law is being stated in the following item, you can write your answer in the
comment section below.
1. It states that for any closed loop path, the sum of the length elements times the
magnetic field in the direction of the length element is equal to the permeability times
the electric current enclosed in the loop (Ampere's Law)
2. A fundamental quantitative relationship between an electric current and the magnetic
field it produces, based on the experiments in 1820 (Biot-Savart Law)

Did you get all the correct answers? Very good. It looks like we are all ready for our next
discussion.
Lesson Proper To answer these questions, we need to talk briefly about electric fields but don’t worry
with because this will be very short. A charge place at a given point in space will generate an
Application electric field around it, the strength for that field at a given position is represented by a given
vector, the magnitude and direction of this vector represent the magnitude and direction of the
force that would experience the positive charge of 1 coulomb place at that position. Now
imagine a metallic bar and focus on one of electrons in the bar. This electron creates an
electric field around it, then connect the bar to a source of alternating current, the electron will
move back and forth in the bar with the current it will oscillate, and so will the direction of the
electric field, the electron generates, this idea is the key point.

If you look of how the y-component of the electric field strength vector changes with time, it
is oscillating and it can be represented by a beautiful cosine or sine curve.
In the second part of 19th century, Maxwell showed that the changing electric field generate a
changing magnetic field and vice versa. So the oscillation of electric field always generates a
magnetic field that oscillate too. Let’s go back to our electron, suppose now that I choose for
the AC current a frequency of oscillation of 10 kHz this means that the electrons oscillate
10,000 times per second, and so does the electric field it generates as well as the induced
magnetic field.

Imagine now that I placed another metallic bar in the oscillating electric field, the electrons in
this bar will feel an oscillating force, yes they are in electric field so they will feel a force, they
will start to oscillate too. What we did here is we transmit to the signals through space.

This is how radio works, we have two antennas, the first bar is emitting signals, the second bar
is receiving the signals when the oscillating magnetic field is generated by the first bar it
 propagates through space through the speed of light. The oscillating electromagnetic field is
what we referred as electromagnetic wave or EM wave and it is most commonly referred as
light.

For example, let us increase the frequency of alternating current up to 10 trillion Hz, the
electron in the bar will oscillate up to 10 trillion Hz and so the electric field it generates, the
resultant EM wave will be infrared radiation. Let us increase the frequency a little more up to
1 quadrillion Hz, the metallic bar starts to glow up it emits visible lights.

Just like the kinds of waves, electromagnetic waves have amplitude, wavelength and
frequency, but instead of different frequencies producing different pitches like sound waves
different frequencies of electromagnetic waves produce different kind of light, if the light is
visible these frequencies will corresponds to different colors, frequencies greater than this will
exists as UV radiations, x-rays and gamma rays and frequencies lesser than this will exists as
infrared, microwaves and radio waves. All of these phenomena are collectively referred to as
electromagnetic radiation and they can be found on electromagnetic spectrum. Here we can
see all the frequencies and wavelength ranging from radio waves to gamma rays, and we have
found some technological use for all of these in modern society.

Even though they seem dramatically different some requiring antennas or other equipment to
manipulate all of them are fundamentally the same thing as the light that you can see with
your eyeballs, they are just of different wavelength. All electromagnetic radiation moves with
the speed of light which is about 300,000,000 m/s in a vacuum. The fastest speed possible in
the universe. This is fast enough to get from here to the moon in about a second and since we
know that all waves move at a speed equal to their wavelength times their frequency this
product will be equal to the speed of light for any type of electromagnetic radiation.
Guided Let’s check comprehension!
activity
Fill in the blanks

Microwaves, gamma rays, and radio waves are all type of _______________________.
Light consists of oscillating ____________ and ______________ fields.
Light in a vacuum always moves at roughly ________________ m/s.
Generalization To sum up our discussion, complete the given activity on page 7, What I have Learned.

Directions: Identify the term/s being referred to in each blank. Choose from the box your
answer. Write you answer in your Science notebook.

Electromagnetic waves are ______________ waves with a wide range of properties and uses.
EM waves can travel not only through air and solid materials, but also through ____________
of space. Electromagnetic waves can be separated into seven distinct groups in
the______________. The behavior of an electromagnetic wave in a substance depends on its
_____________ or _____________. Maxwell's calculation of the speed of an electromagnetic
wave included two important constants: the _______________ and _______________ of free
space. The speed of an electromagnetic wave comes directly from a fundamental consideration
of ______________ and ________________.

transverse permittivity magnetism

spectrum electricity
vacuum frequency
wavelength permeability
Evaluation To check your understanding, accomplish the attached worksheet in your module. You will be
given 15 minutes to accomplish the task.

Were you able to answer all the questions?

Very good. Keep up the good work!
Assignment Now for your assignment, answer
I hope you enjoyed our lesson and understood our lesson.
Once again, I’m Teacher Kaye Lim where everything’s KAYE OK in KAYE’S VIRTUAL
CLASSROOM.

Prepared by:

PRINCESS KAYE M. LIM

Teacher II