Methods of Teaching Science
(SED 525S & 525SL)
Assignment #4 – “Presenting a Demonstration”
Dean Papadakis – October 2, 2007
Do Microwaves Exit the Oven?
Can We “See” Where Are The Microwaves?
Can We Predict the Final Temperature of a Beaker of
Water Placed into Microwave?
Principles:

Wavelength and Frequency of Electromagnetic
Radiation

How does a microwave differ from a light wave?

Inverse-Square Law

Metric Conversions (e.g. Mega)

Energy Conservation Using Energy In = Heat Out
California State PHYSICS Standards
Grades 9-12
Here are the standards that can be applied to this demonstration!
Heat and Thermodynamics
3. Energy cannot be created or destroyed although in many processes energy is
transferred to the environment as heat. As a basis for understanding this
concept, students know:

heat flow and work are two forms of energy transfer
between systems

thermal energy (commonly called heat) consists of random
motion and the vibrations and rotations of atoms
and molecules. The higher the temperature, the greater the
atomic or molecular motion
Waves
4. Waves have characteristic properties that do not depend on the type of wave. As
a basis for understanding this concept, students know:

waves carry energy from one place to another

how to identify transverse and longitudinal waves in mechanical
media such as springs, ropes, and the Earth (seismic waves)

how to solve problems involving wavelength, frequency, and
wave speed.

radio waves, light and X-rays are different wavelength bands
in the spectrum of electromagnetic waves whose speed in vacuum
is approximately 3x108 m/s (186,000 miles/second).

how to identify the characteristic properties of waves:
interference (beats), diffraction, refraction, Doppler effect, and
polarization.
California State CHEMISTRY Standards
Grades 9-12

how to solve problems involving heat flow and temperature changes,
using known values of specific heat, and latent heat of phase change.
Materials:





Microwave Oven
Incandescent Light Bulb
Fluorescent Light Bulb
400 mL beaker
Calculator
Procedures:
Part I.
Do Microwaves Exit the Oven?
1.
First we ask students if visible light can leave the oven, when it is turned
on. By turning on the oven for a few seconds, we can confirm their
answer by seeing that light does indeed leave the oven through the door
window.
2.
Next we ask if microwaves are the same type of wave as visible light.
3.
When students (hopefully) answer, yes, we then ask a third and final
question. Do the microwaves also leave the oven through the window?
4.
To answer this question, we will want to determine the wavelength of the
microwaves created in the oven by reading the microwave label.
The wavelength is not stated, but the frequency of the microwaves is
stated on a label, which is either inside or outside of the oven. Make sure
that you read the correct frequency. That is the frequency of the
microwaves and not the frequency of the A.C. electrical current.
5.
6.
We next do a calculation and convert the frequency into a wavelength
using the speed of light and the stated frequency and the equation,
c=λf
7.
Now we can compare the wavelength of the microwaves with the
wavelength of visible light, which is 400 nm to 700 nm.
8.
Relate the size of the microwave wavelength and visible light wavelength
to the diameter of the holes in the screen which is in the oven door. You
can do this by actually measuring the size of the holes with a ruler. If you
have access to a flexible camera that can be projected, students can clearly
see the size of the holes.
Part II.
Can We See Where Are The Microwaves?
1. Now, to examine how the microwaves generated in the oven can interfere
constructively with each other, we will place a light bulb (incandescent or
fluorescent) into a 400 mL beaker of water, so that the metal base of the bulb
is covered by water.
2. Place the beaker with the light bulb into the microwave oven in the middle of
the oven and then turn on the oven for about 8-10 seconds, and observe what
happens to the bulb.
3. Next, repeat the experiment, after moving the beaker closer to the edge of the
oven, and again turn on the oven for the same amount of time as before, and
again observe what happens to the light bulb.
How do we explain the results?
Part III. Can We Predict the Final Temperature of a
Beaker of Water Placed into Microwave?
1. Determine the power output of the microwave oven, e.g., 1000 Watts or 1200
Watts.
2. Measure 400 mL of water and place into a 600 mL beaker.
3. Calculate and predict what temperature increase the water will experience,
by using Q = Specific Heat of Water x mass of water x Δ temperature
4. Next measure the initial temperature of the water and place it into the
microwave oven and turn it on for 50 seconds.
5. After the water is heated, remove the beaker and measure its final
temperature.
6. How does the actual temperature increase or change, compare to the change
that you predicted? If it is not close, consider where you placed the beaker of
water in the oven.
Student Prior Knowledge:
(Students should have a basic understanding of the following concepts)
 Understanding metric units such as Mega
 The wave equation c
=λf
 Energy can be carried in the form of a wave
 The inverse square law
 Calculating the energy output and input by using conservation
of energy
Explanation of the Demonstrations:
Part I
Do Microwaves Exit the Oven?
First, we posed the following three questions:
a) When a microwave oven is turned on, can you see the light
leaving the microwave oven, through the oven door?
YES!
Next,
b) Are visible light waves and microwaves both a part of the
same electromagnetic spectrum?
YES! See below:
+ Visit NASA.gov
+ Science@NASA
+ IMAGERS Home
RADIO WAVES | MICROWAVES | INFRARED | VISIBLE LIGHT | ULTRAVIOLET | X-RAYS | GAMMA RAYS
700 nm
↔
400 nm
Visible light waves are the only electromagnetic waves we can see. We see these
waves as the colors of the rainbow. Each color has a different wavelength. Red has
the longest wavelength and violet has the shortest wavelength. When all the waves
are seen together, they make white light.
If we round off the wavelength of red light (700 nm) to
1000 nm, this becomes 1 μm, which is equivalent to 1/1,000
of one mm or 1/1,000 of the width of a paper clip wire.
VERY SMALL!
See picture below:
The wavelengths of Light waves are about
1/1,000 the size of these holes.

When white light shines through a prism, the white light is broken
apart into the colors of the visible light spectrum. Water vapor in the
atmosphere can also break apart wavelengths creating a rainbow.
Each color in a rainbow corresponds to a different wavelength of the electromagnetic
spectrum.
http://science.hq.nasa.gov/kids/imagers/ems/visible.html
↑ ↑
visible microwave
light
light
http://saturn.jpl.nasa.gov/mission/images/EM-spectrum-th.jpg
Last Question:
c) If visible light waves and microwaves are in fact a
part of the same electromagnetic spectrum, then why
don’t we worry about microwaves leaving the oven
just like light does?
Let’s begin to answer this last question by reading the frequency
of the oven’s microwave radiation from the label on the oven.
"12. V.A.C. 7.44 kW 60 Hz Single Phase Output 700 W
2450 MHz. Complies with DHHS Radiation Performance
Standards 21CFR Subchapter J."
http://hypertextbook.com/facts/2004/LindseyTannenbaum.shtml
Now we need to convert this frequency to wavelength. We know the
speed of microwave light = c and
c = 3 x 108 meters/second
or
(186,000 miles/second)
so we can use the equation, c = λ f and then rearrange
this equation to solve for (λ) wavelength
λ = c/f
First, the frequency, 2450 MHz is equivalent to 2450 x 106 Hertz, so
The wavelength of microwaves, λ =
3x108 m/s = 0.12 m or 12 cm
2450 x 106 Hz
So, we see from this that the microwaves are about
120 times longer in wavelength than the diameter of
the holes in the oven door, (120 mm/1 mm) and
therefore should not be able to pass through the door,
as light can.
Part II. Can We See Where Are The Microwaves?
How can we really “see” that microwaves are being
produced in a microwave oven? We learned in the
previous question, that food must have “polar” water
in it, in order to heat the food. And we can taste the hot
food after being warmed, but is there anything else that
can also be heated by the microwave radiation, which
we can SEE?
We know that microwave radiation gets absorbed by water molecules, but
can pass through (and therefore not get absorbed by) glass or plastic. If we
place a light bulb (incandescent or fluorescent) into a beaker of water, so that
the water covers the metal base of the bulb, and then place the beaker into the
microwave oven, and turn it on for 10 seconds, we will see an interesting
result.
Below is a short video I took, using a fluorescent type of bulb.
We are seeing in this video, that microwaves must be passing
through the glass of the light bulb, and that they are exciting the
atoms of the gas in the bulb, causing it to emit light.
Here is another short video I took, using an incandescent 40 W light
bulb. Notice that as it rotates in the oven, colors appear and the
brightness varies, depending on the position in the microwave.
This means that the microwaves (which come from one location in
the oven) are reflecting off of the oven’s walls, and interfering with
each other, both constructively and destructively. When they
interfere constructively, the amplitude or intensity is increased and
you notice it by seeing the gases in the light bulb get excited, and
then they emit visible light.
Two images are shown below:
When microwaves interfere CONSTRUCTIVELY, as
shown above, and they pass through the light bulb
glass, the bulb lights up.
When microwaves interfere DESTRUCTIVELY, as
shown above, the waves cancel with each other and
the light bulb remains unlit.
Here are some other videos from the Web that you can watch!
http://www.ac.wwu.edu/~vawter/PhysicsNet/QTMovies/Inductance/Bulb-inMicrowaveMain.html
The first video below shows the importance of the beaker of water.
http://hackedgadgets.com/2007/01/07/light-bulb-in-microwave/
Part III. Can We Predict the Final Temperature of a
Beaker of Water Placed into Microwave?
(Mechanical Equivalent of Heat)
After noting the power output of the microwave oven, we can convert this power
value to an energy value: 1,000 Watts x 1 Joule/sec per Watt = 1,000 Joules/sec
If we turn on the microwave oven for, let’s say, 50 seconds, then this corresponds
to 1,000 Joules/sec x 20 seconds or 20,000 Joules of energy being output by the
microwave oven.
This means that if we heat water with this amount of energy, then the water
should absorb 50,000 Joules of energy. This can then tell us how much the
temperature of the water should increase.
For example, if you were to measure 400 mL of water and place it into a beaker,
we can calculate and predict how much the temperature of the water should
increase, if it absorbs 50,000 Joules of energy from the microwave oven.
Since Q = Specific Heat of Water x mass of water x Δ temperature, we can
calculate the Δt as 20,000 Joules/1 calorie per gram-degree x 400 mL x 1 gram/mL
which is then a 50° C temperature change. So if the water begins at 25°, then its
final temperature should be 75°.
So next we actually measure the water’s initial temperature and then place the
beaker into the microwave oven and heat it up for 20 seconds. When it is finished,
we measure its final temperature and see if it has risen by 50  C.
CC
The experiment described above, was first done by James Prescott Joule who
discovered a principle known as the “Mechanical Equivalent of Heat”.
Here is an image of his experiment:
http://www.physchem.co.za/Heat/Graphics/Heat27.gif
QUESTIONS AND ANSWERS
Some thought provoking questions:
1.
If a microwave oven had a leak at the door, and
microwaves were able to escape, what would be a safe
distance from the oven, for a person? For example, If
you were 2 inches from a leaking microwave
oven and you received 5 milliwatts of microwave
radiation per square centimeter, how much
radiation would you receive if you were 20
inches away (almost two feet)?
The inverse square law will help us with this question.
All microwave ovens made after October 1971 are covered by a safety
standard enforced by the FDA. The standard limits the amount of
microwaves that can leak from an oven. The limit is 5 milliwatts of
microwave radiation per square centimeter at a distance of two inches from
the oven surface. This is far below the level known to harm people.
Furthermore, as you move away from an oven, the level of any leaking
microwave radiation that might be reaching you decreases dramatically. For
example, someone standing 20 inches from an oven would receive
approximately one one-hundredth of the amount of microwaves received at 2
inches. (Radiation =1/(distance)2
So, if you double your distance from the microwave oven, you not
only decrease the radiation you might receive, but it decreases to onefourth of the amount, not one-half.
http://www.hps.org/hpspublications/articles/microwaveovens.html
2.
How do microwaves heat food and why aren’t they as
efficient at heating up other types of materials, such as
glass and plastic?
Microwaves are a form of electromagnetic energy, like light waves or radio
waves, and occupy a part of the electromagnetic spectrum of power, or
energy. Microwaves are very short waves of electromagnetic energy that
travel at the speed of light (186,282 miles per second). In our modern
technological age, microwaves are used to relay long distance telephone
signals, television programs, and computer information across the earth or
to a satellite in space. But the microwave is most familiar to us as an energy
source for cooking food.
Every microwave oven contains a magnetron, a tube in which electrons are
affected by magnetic and electric fields in such a way as to produce micro
wavelength radiation at about 2450 Mega Hertz (MHz) or 2.45 Giga Hertz
(GHz). This microwave radiation interacts with the molecules in food. All
wave energy changes polarity from positive to negative with each cycle of the
wave. In microwaves, these polarity changes happen millions of times every
second. Food molecules - especially the molecules of water - have a positive
and negative end in the same way a magnet has a north and a south polarity.
In commercial models, the oven has a power input of about 1000 watts of
alternating current. As these microwaves generated from the magnetron
bombard the food, they cause the polar molecules to rotate at the same
frequency millions of times a second. All this agitation creates molecular
friction, which heats up the food. The friction also causes substantial damage
to the surrounding molecules, often tearing them apart or forcefully
deforming them. The scientific name for this deformation is "structural
isomerism".
By comparison, microwaves from the sun are based on principles of pulsed
direct current (DC) that don't create frictional heat; microwave ovens use
alternating current (AC) creating frictional heat. A microwave oven
produces a spiked wavelength of energy with all the power going into only
one narrow frequency of the energy spectrum. Energy from the sun operates
in a wide frequency spectrum.
http://www.lessemf.com/mw-stnds.html
The answer above, relates directly with the California State Physics
Standard for Heat and Thermodynamics:
Thermal energy (commonly called heat) consists of random motion
and the vibrations and rotations of atoms and molecules.
The higher is the temperature, the greater the atomic or molecular motion.
http://www.csun.edu/science/standards/science/physics_standards.html
3.
In the mechanical equivalent of heat experiment using
the microwave oven, why would you not want to heat
the water for too long of a time?
If you heat the water for too long of a time, so that it starts boiling,
then the energy that is being output to the water, is simply potential
energy that is being used for the phase change, and it is not kinetic
energy that is being used for heating up the water.
Applications to Everyday Life
#1
By understanding the relationship between wavelength and
frequency, with the example from the microwave oven, we can
apply this concept to other forms of electromagnetic radiation,
such as Radio Waves or Ultraviolet Rays.
For example, if we ask the question, “Why are AM radio waves
affected when a car radio passes through a tunnel, while FM
radio waves are NOT affected when passing through a tunnel?
Answer: The wavelength of an FM radio wave is about 2-3 meters in
length, which is smaller than the diameter of a typical tunnel. AM
radio waves on the other hand are about 500 m long, which is
considerably wider than the diameter of the tunnel, and so
consequently these waves get blocked by the tunnel.
#2
The inverse-square law applies to many situations. For
example, a technician in a dentist’s office or a doctor’s office,
who is administering X-rays to a patient, should know this law
because by simply doubling or tripling the distance between
them and the source of the X-rays, they reduce the intensity of
the X-rays by a factor of 4 or 9, respectively.
#3
Knowing that microwaves can pass through glass and excite
the atoms of the gas inside of a light bulb, we could use this as a
test for whether or not a microwave oven is leaking through the
door. We can place a very low wattage (1.5 Watt) neon bulb or
other type of bulb, next to the door of a microwave oven, while
it is on and then turn off the lights and see if the bulb lights up
at all. If it does, this can be an indication that the oven may be
leaking.
#4
Another application of microwaves is with the use of a set of
Radio Shack signal emitter and receiver for a flexible camera.
The “flex cam” sends its signal to a t.v. using a microwave.
Therefore, maybe it is possible to test whether a microwave is
leaking by placing the receiver next to the microwave while it is
on.
This microwave detection experiment did not work because when the microwave
oven was turned on, the t.v. that was connected to the microwave receiver, showed
lines moving on the screen, even when the detector was not next to the oven. This
may be due to the fact that they were on the same electrical circuit.
Who invented microwave ovens?
The Nazis, for use in their mobile support operations, originally developed microwave
"radiomissor" cooking ovens to be used for the invasion of Russia. By being able to
utilize electronic equipment for preparation of meals on a mass scale, the logistical
problem of cooking fuels would have been eliminated, as well as the convenience of
producing edible products in a greatly reduced time-factor.
References
http://science.hq.nasa.gov/kids/imagers/ems/visible.html
http://saturn.jpl.nasa.gov/mission/images/EM-spectrum-th.jpg
http://hypertextbook.com/facts/2004/LindseyTannenbaum.shtml
http://www.hps.org/hpspublications/articles/microwaveovens.html
http://www.lessemf.com/mw-stnds.html
http://www.csun.edu/science/standards/science/physics_standards.html
http://www.ac.wwu.edu/~vawter/PhysicsNet/QTMovies/Inductance/Bulb-inMicrowaveMain.html
http://hackedgadgets.com/2007/01/07/light-bulb-in-microwave/
http://www.physchem.co.za/Heat/Graphics/Heat27.gif
My reflections from student comments from class!
All of my comments are listed individually underneath
each commenter and then I have combined my
comments all together at the end of this document.
Message 18 from Kali Nicholas in course SED525S METH TCH SCIENCE
- Herr (14922
- Fa07)]
DeanGreat job, so interesting! To further engage the students I
would use a more excited
tone
of voice. It may be a good idea to have the students help you
with calculations
or have
students join together to compare the different sizes of
wavelenghts. For example
have a
hula-hoop and one student can fit through it, but ten joined
together can't.?
Or just have a
student help you or check to see you are really putting a light
bulb in the microwave.
Great
job though!
Cheers,
Kali
I love the hula hoop idea from Kali, by having students step
through the hula hoop to help them see the concept of light
waves being able to fit through the holes in the microwave
door just like a person fitting through a hula hoop.
I did not realize that my voice is monotone and having a
more exited voice will help me.
************************************************************
[Message 17 from Dora Preminger in course SED525S METH TCH
SCIENCE - Herr (14922
- Fa07)]
interesting!
maybe leave out the Nlogy with the weight and pulley? I thought
it was confusing.
explain better why the bulbs light up
I see now that I tried to put too much into it and taking
out the analogy with the weight and pulley will help to
allow more time to better explain why the bulbs light up.
************************************************
[Message 15 from Juan Velazquez in course SED525S METH TCH
SCIENCE - Herr (14922
- Fa07)]
Dean, excellent job, I need to try it out at home (real life
application bonus points!).
Before
explaining it I would go straight into the demo to further engage
the students.
At the end
perhaps you should mention the application of the concepts to
other problems/applications.
I can see your handout is an excellent resource, thanks for
putting it up!
I was actually thinking during the presentation that
everyone was anxious to see what I was going to do with the
microwave oven and so doing the demonstration right away
would help the students to become engaged right away and be
curious about how it worked.
************************************************
[Message 14 from Arlena Tupaz in course SED525S METH TCH SCIENCE
- Herr (14922
- Fa07)]
HEY DEAN,
Since time is the essence in the demo, i do understand why you
were not able to
do the
assessment part but i'm quite sure you have one for the class
considering you
have the
PPT presentation. Always check for understanding.
Anyway, it was cool to see
bulbs light up in a microwave.
NICE JOB DEAN!
Arlena
I think that I was not really checking for understanding
because I felt the pressure of time, however, it is really
important to do and I will try to remember to always do
that, even at the expense of time.
************************************************
[Message 13 from Shadi Eliaspour in course SED525S METH TCH
SCIENCE - Herr (14922
- Fa07)]
Great presentation loved it! Very good presentation easy to
follow the
only suggestion I have is to may be change the tone of your voice
up and
down while going through the powerpoint.
May be take out some of the information in the powerpoint make it
a
little concise. Good job!
This is the second comment about the tone of my voice being
monotone and so it really must be true. I can only hope
that I don’t come across that way to my own students,
however, if students in this class are detecting it, then
it probably is happening with my own students too. I agree
that I had too much information and felt rushed the whole
time. I should shorten it by taking out some of the
details and focusing on fewer topics.
************************************************
[Message 12 from Hugh Sutherland in course SED525S METH TCH
SCIENCE - Herr (14922
- Fa07)]
Microwave itself was in the way of the projector at the start of
the demo.
Effectively moved students
so they could see into the microwave.
The recessed nature of the microwave did limit the overall
visibility
and you consistently attempted to overcome this.
Good job!! Very well prepared!!
A flexible camera hooked up to the t.v. would help students
to see better into the microwave oven. This is something I
use in my own classroom at South Pasadena High School.
************************************************
[Message 11 from Afrodita Fuentes in course SED525S METH TCH
SCIENCE - Herr (14922
- Fa07)]
Wow! this is all new to me. Very concise and clear questions.
Nice flow of activities.
Absolutely relevant to everyday experience. I may be able to add
more things later.
thanks,
Afrodita
I appreciate the positive comments as well as the “negative”
comments.
************************************************
[Message 10 from David Baca in course SED525S METH TCH SCIENCE
Herr (14922 Fa07)]
-
Good that you presented the goals for your presentation.
Very dramatic use of microwaves on light bulb. Really held my
interest.
I like the way you had all of your projected images packaged into
one document.
Saved
time in shifting from one phase of your presentation to another.
I really believe that stating the goals of a demonstration
is important for students recollection and understanding.
Maybe for sake of time, I could have reduced the goals from
three to one or two.
************************************************
[Message 9 from Alexandra Carlton in course SED525S METH TCH
SCIENCE - Herr (14922
- Fa07)]
8. Understanding - For the most part you gave a good explanation
of the
experiment, however it would work even better if you explained
how
microwaves heat things, particularly water and the way heat
absorption
works.
Side note, not that it's relevant to your demo, because you never
heated
the water for very long, but as a safety reminder, microwaving
the same
cup of water over and over again is a very good way to superheat
it, and
so you might want to remind your audience not to use the same
water when
they try it at home, etc.
I was actually thinking that it would be interesting to get
into how microwave heat things. Especially since most
people believe that the food is heated from the inside out
when in fact it is heated from the outside in.
Alex gave a very good safety comment, which I should model
for my students. That is that I should change the water
every time I heat the water so that it does not get
superheated.
************************************************
[Message 8 from Benjamin Kay in course SED525S METH TCH SCIENCE
- Herr (14922 Fa07)]
you over achiever you-well done! great visuals. you will need a
dark room for
this, so
maybe take a field trip to the dark room of the photography lab
or perform in a
store
room. your picture on your document, where you show the paper
clip against the
microwave holes....maybe show part of the microwave in the photo
so that we can
tell
that the holes in the picture belong to a microwave.
Great comment about showing the whole microwave in the
picture with the paper clip, so that students see the whole
perspective. I had difficulty trying to get the detail or
magnification I needed, while also showing the whole
microwave oven. Maybe a second picture would help.
************************************************
[Message 7 from Jennifer Witman in course SED525S METH TCH
SCIENCE - Herr (14922
- Fa07)]
HiGreat Job!
When introducing Mega- try remind students of Mega byte (MB)
with
computers. Many of them actually know how they relate to kB and
GB from
experience even if they don't know the factors involved.
I'll definitely use this with my students... I just need to find
a
microwave oven that the teachers won't miss a few hours...
My thanks,
Jenny Witman
Again, this is a good comment about making student
connections to the real world, e.g. to MB and kB with
computers, so that students see the connection to something
they are familiar with.
************************************************
[Message 6 from Denise Hobbs in course SED525S METH TCH SCIENCE
- Herr (14922 Fa07)]
Significant?
Not for 7th grade life science, but yes to physics.
Explained Correctly?
Yes. Be sure to go through information slowly and clearly.
frequently to
check for
understanding.
Stop
Good job.
Denise
This is the second time someone said to check for
understanding and to slow down a bit making my presentation
more clear. I guess I was in a hurry and I should not
compromise my presentation that way.
************************************************
[Message 5 from Carol Cao in course SED525S METH TCH SCIENCE
Herr (14922 - Fa07)]
-
You did a great job explaining all the concepts! I was very
intrigue
because you used an everyday item, which will be great for
students.
Great job getting them hooked.
I liked how you broke it up into 3 clear parts. This makes it
much
easier for students to follow along. Plus, you did assessments
throughout the demo, which can be a good way to gauge the
understanding.
You had great applications to everyday life and things in our
class.
For a high school science class, it would be great to come up
with more
applications to students' lives.
There was a lot of concepts in your demo. It might be a little
hard to
cover all the concepts all in one demo. However, all three parts
were
related to each other.
Glad




that I included all of these great things:
getting them hooked,
breaking up demo into different parts,
having assessments throughout the demonstration,
stating applications to everyday life.
Having more connections would be better and reducing the
number of concepts I include would help.
************************************************
[Message 4 from Stacy Tanaka in course SED525S METH TCH SCIENCE
(14922 Fa07)]
- Herr
A suggestion for an everyday life application is the idea of microwaves
and cancer. I think this site had a little bit on it.
http://www.cancer-health.org/Brain_cancer.html
Cool presentation!
Making a connection between microwaves and cancer would be
interesting. More time would be needed and this could be
done as a follow up to this demonstration, or maybe making
it a homework assignment to check out would get them more
engaged.
************************************************
[Message 3 from Eric Holt in course SED525S METH TCH SCIENCE
(14922 - Fa07)]
- Herr
Have you thought about doing the demo first? I have this image of the
8th graders
all
freaking out b/c they think you are going to blow up the classroom.
Then they will
be
interested in why it does not.
Someone else mentioned doing the demonstration first instead
of talking first. For 8th graders, this would be very
important. For high school students, I think they could
handle the introduction first before the demonstration, as
long as it does not take too long for the intro.
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All of my comments are pooled together here for flow of reading:
I love the hula hoop idea from Kali, by having students step
through the hula hoop to help them see the concept of light
waves being able to fit through the holes in the microwave
door just like a person fitting through a hula hoop.
I did not realize that my voice is monotone and having a
more exited voice will help me.
I see now that I tried to put too much into it and taking
out the analogy with the weight and pulley will help to
allow more time to better explain why the bulbs light up.
I was actually thinking during the presentation that
everyone was anxious to see what I was going to do with the
microwave oven and so doing the demonstration right away
would help the students to become engaged right away and be
curious about how it worked.
I think that I was not really checking for understanding
because I felt the pressure of time, however, it is really
important to do and I will try to remember to always do
that, even at the expense of time.
This is the second comment about the tone of my voice being
monotone and so it really must be true. I can only hope
that I don’t come across that way to my own students,
however, if students in this class are detecting it, then
it probably is happening with my own students too. I agree
that I had too much information and felt rushed the whole
time. I should shorten it by taking out some of the
details and focusing on fewer topics.
A flexible camera hooked up to the t.v. would help students
to see better into the microwave oven. This is something I
use in my own classroom at South Pasadena High School.
I appreciate the positive comments as well as the “negative”
comments.
I really believe that stating the goals of a demonstration
is important for students recollection and understanding.
Maybe for sake of time, I could have reduced the goals from
three to one or two.
I was actually thinking that it would be interesting to get
into how microwave heat things. Especially since most
people believe that the food is heated from the inside out
when in fact it is heated from the outside in.
Alex gave a very good safety comment, which I should model
for my students. That is that I should change the water
every time I heat the water so that it does not get
superheated.
Great comment about showing the whole microwave in the
picture with the paper clip, so that students see the whole
perspective. I had difficulty trying to get the detail or
magnification I needed, while also showing the whole
microwave oven. Maybe a second picture would help.
Again, this is a good comment about making student
connections to the real world, e.g. to MB and kB with
computers, so that students see the connection to something
they are familiar with.
This is the second time someone said to check for
understanding and to slow down a bit making my presentation
more clear. I guess I was in a hurry and I should not
compromise my presentation that way.
Glad
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that I included all of these great things:
getting them hooked,
breaking up demo into different parts,
having assessments throughout the demonstration,
stating applications to everyday life.
Having more connections would be better and reducing the
number of concepts I include would help.
Making a connection between microwaves and cancer would be
interesting. More time would be needed and this could be
done as a follow up to this demonstration, or maybe making
it a homework assignment to check out would get them more
engaged.
Someone else mentioned doing the demonstration first instead
of talking first. For 8th graders, this would be very
important. For high school students, I think they could
handle the introduction first before the demonstration, as
long as it does not take too long for the intro.