Lab Day-11.2.17

Radio antenna tour (depending on weather)
Note wavelength, shape, focusing and overall size
Inverse square law: butter gun
dB and focusing: 3 dB (laptop antenna) vs 30 dB (dish antenna)

java and html5 sims (see previous weblog)

Review sims-see pages

Determine the efficiency of the microwave oven.
Look up Watts
Heat a mass of water in an insulated cup
Measure temperature change
Calculate energy captured as heat
Calculate energy expended
Calculate efficiency


ch 24: Electromagnetic Waves/Radiation

First, let's start with the radio from last chapter:

Recall that this created an oscillating electric current between the L and C. Recall also that this mirrored a similar mass/spring system. Make sure to keep these in mind.
Now, try this:
Download file "radio-waves_en.jar"

Play with the frequency of the charge up and down the antenna, and notice how the fields around the antenna change

Check out this image of current in the wire/antenna:

Notice the sine wave pattern of the electric current.
Now for the field this creates:

Make sure to verify this using your right hand rule.
Notice in the middle frame how the B field is always 90° to the E field.
This is the hardest part of EMR to understand...
Note also that Maxwell found this:

Connecting electricity (the Eo part) with magnetism (the uo part). This is true for all EMR from light to radio waves (not sound or earthquakes though, they are not EMR, but are compression waves in a medium)
Since the E field creates the B field which creates the E field, Light and other EMR needs no medium, but the speed of this radiation depends on Eo and uo for that medium, so the speed of light IN A VACUUM is about 3 ee8 m/s

One more tough bit: E/B =c
Think this over: if the fields are creating each other, then their ratio has to remain constant (look at the picture above).


Recall from your study of waves that:

Velocity = frequency x wavelength
or in the case of light and EMR:

Easy, now we can calculate the wavelength of any EMR wave.
Example: pick your favorite radio station. Find the frequency (FM is fun). Your car antenna should be 1/4 of the wavelength to receive this station best. How long should your car antenna be?

Repeat this with a frequency of 2.4 gHz. What will be the wavelength? Why is this interesting?

The EMR spectrum (VERY interesting):

Keep in mind that as frequency increases, wavelength decreases (their product is a constant, c).
Keep in mind also that higher frequencies have higher energies (you have not learned this yet, but compare IR light to UV light-which one will give you a sunburn).

Also: the higher the frequency, the less the impact of diffraction (travel around corners), so 2.4 gHz needs to be line of sight, while HF radio (14 mHz) can bend a bit.

3 ISM bands: 900 mHz, 2.4 gHz, 5.8 gHz

Radio is a cool example of this: FM radio is frequency modulation:

While AM radio is amplitude modulation:

Interestingly, the signals from your ear to your brain are also FM. Why?

More bits:
Intensity is not power, but they are related. You may find this with other wave phenomena like earthquakes. In the case of EMR, we use these formulae:
for the E field version

for the B field version,
and combined:

While you may never see these on an AP exam, if you go into physics in college, they will certainly show up. Notice where Eo and uo show up in each.

Fun with spectra:
Microwaves (ovens, ISM band wifi)
Radar (square wave pulses)
UV, ozone layer, three types of UV
cosmic rays

Each of these travels at about 3 ee 8 m/s.
Look up the blue glow in nuclear reactors, called Cherenkov radiation...

Determine the efficiency of the microwave oven.
Look up Watts
Heat a mass of water in an insulated cup
Measure temperature change
Calculate energy captured as heat
Calculate energy expended
Calculate efficiency

Download file "microwaves_en.jar"
Download file "molecules-and-light_en.html"
Download file "color-vision_en.html"


LC circuits, radio


Download file "circuit-construction-kit-ac_en.jar"

Download file "circuit-construction-kit-ac-virtual-lab_en.jar"

Try creating a "tank circuit" with a battery, switch, capacitor and inductor. Charge the capacitor, then open the switch.
Monitor the current and voltage in your tank circuit, and change the voltage of the battery, values for C and L. Calculate a resonant circuit and notice the amplitude of the sine wave (AC) you can create. Explore!

Here's how it works in a radio:
If you add headphones and a diode (rectifier) you can listen to AM radio (yes, it is really that simple):

(b) is the AM (amplitiude modulated) radio wave
(c) is the wave after the rectifier (diode) only allows the positive side to pass
(d) is the music you want to hear

1. create an LC circuit, charge it, and notice the frequency of the oscillation
2. design an LC circuit with specific L and C values, predict frequency and see if this matches what you see in the simulation
3. drive your designed circuit with AC voltage, sweeping below, at and above the resonant frequency, note the amplitude of the waves in the "tank" circuit

Next: Electromagnetic Radiation (EMR)
First, some simulations:

Download file "radio-waves_en.jar"

Download file "faradays-law_en.html"


Chapter 23 Induced EMF (finally)

Flux comes from the latin word for "flow"
Think of a water flume (square pipe) of width w and height h. Area = w x h
Units for this would be m x m or m^2
Now add the velocity of the water, which would be in meters/second (m/s)
Flux would be the area x velocity, or m^2 x m/s
What units would we have for flow then?
m^3/s which is really like a volume per second unit...
Now, imagine holding your hand in this water current: flat hand vs. sideways hand: which has more resistance?

In electromagnetism, we use B as the velocity part, and area is still the area part:

Note that the B is the field, A is the area, and cos theta is the angle FROM NORMAL. (like the hand in the water)
So if theta is 0°, then Cos theta is 1 (max exposed area, think of yourself in a windstorm)


If the flux changes FOR ANY REASON, this will generate an electric current (flow) in a conductor. N in this case is the number of turns of wire seeing this changing flux.

n.b. (nota bene): Flux can change by changing the angle, the area exposed, OR the magnitude of the B field.

Lenz's law: Just like F -ma or Le Chatelier's principle (the law of equilibrium) in chemistry...
Things resist the change exerted on them:
F = ma Masses resist a force making them accelerate. If no acceleration, there is no force (remember?)
Le Chatelier's principle: (look this up)
Eddy Currents and magnetic damping:
Generated current is shorted out in the material

Magnetic stove tops: same deal, they only work with certain cookware (iron or steel, not aluminum)

Small omega (looks like w) means rotational velocity in radians per second
Be careful in calculations with this, make sure your calculator us usually set for degrees

emf = 2Blvsinwt

But since most generators have many turns of wire, and may have an area we can describe:

emf = NABwsinwt

Or, since emfo is NABw,

emf = emfo sinwt

This is confusing stuff, since rotation was months ago...
Recall that:
t = t
v = w
a = alpha
x = theta in radians

Much more interesting are transformers:
If you magnetically couple a coil with another coil, and pass AC through one, it will induce AC current in the second one:

If the number of turns in the secondary is 2x the turns in the primary, this will be a "step up" transformer, and double the voltage there.
Since P = iV, if the voltage is 2x, then the current is x/2:

23.8-Electrical safety
Grounding: three wire plugs vs. fat one side plugs-why?
GFI or GFCI plugs-find one, test it out
How does it work?
Why will my GFCI outlets all fire if I use my radio transmitter nearby?

23.9 Inductance
L is the symbol, inductance is the ability of a coil (inductor) to create a magnetic field.

The best way to imagine this is to go back to SHM (simple harmonic motion):
Mass is like the inductor (L)
Spring constant is like a capacitor (C)
Friction is like a resistor (R)
Velocity is like current (i)
we call these combinations LRC circuits for this reason...

The energy we can store in a mass-spring system is 1/2kx^2 for the spring part and 1/2mv^2 for the KE part , remember?
The energy we can store in an inductor is like the 1/2mv^2 part of the spring mass system:

Inductors in circuits act like a mass in a system: they resist any change in position or velocity (e.g. acceleration)

Once current stabilizes, inductors (L) act like wires, conducting like a wire.

Capacitors are the opposite, they act like a broken wire when the current stabilizes (in series).

When these components are in parallel, they can block or pass AC current (this is how your graphic equalizer works)

See power supply, graphic equalizer, speaker crossover network, noise filter...

An AC term involving L and C, ALWAYS dependent on frequency:
Reactance is like "AC resistance"

Inductive reactance:

Note that as f approaches zero (DC), "resistance" becomes zero, like a straight piece of wire.

Capacitive reactance:

Note that as f approaches zero (DC), "resistance" becomes infinite, like a broken wire.

Resistors have no change from DC to AC, regardless of frequency

If we combine all three of these, we get something called impedance, which you may have seen on speakers or headphones:

Note that if there is no XL or Xc, the formula becomes Z = R
There are cool vector diagrams of this you might enjoy online...
Another way Z = R could be if XL = Xc:

Do the math on this, and you'll see that:

Invert this for period:

Period =
Does this remind you of a pendulum?

Mass on a spring?


ibook ch 22 notes

Review: E fields vs. B fields
Rowboat in wind example: turns until in line with wind (parallel to field lines)
Cyclotron bubble chamber (liquid hydrogen)
5 particles, same velocity, 5 curves-why?
cyclotron radius: mv2/r = qvB, so r = mv/qB If all v are same, same B field, then depends on m/q or q/m in physics speak (charge to mass ratio). List m/q for proton, neutron, electron, positron, antiproton.
Owen Chamberlain:


E = Blv
Plane example, hall effect
Can measure very small magnetic fields, or propel charged liquids (Magneto hydrodynamics)
All based on the right hand rule F = qvB

F= BiL (my favorite): force on a current carrying wire, related to Hall effect, dependent on right hand rule again

Torque = ni(AxB) or niABsin theta
Can be either a rectangle or a circle, basis for all motors, AC or DC

Field around a current carrying wire
B = u/2π i/r (long wire)
This is Ampere's law

If the wire is in a loop:

If you have many turns, we call this a solenoid (looks like a pipe):

Notice the next right hand rule: thumb is direction of current, fingers show the direction of the B field

Where n is the number of turns, I is the current.

If two wires with current in them are near each other, their magnetic fields will interact, forcing them together or apart:

Next, if you have identical current going in opposite directions, between the conductors the fields will cancel:

The Ampere is defined by these relationships:

Magnetocardiogram (MCG)
Magnetoencephalogram (MEG)


iBook ch 22 notes

  • what is a CME? why should we care?
  • what is EMP? how is it similar to CME? why should we care?
  • ferromagnets vs. electromagnets
  • dipoles vs. monopoles (theoretical)
  • domains
  • curie temp
  • electromagnet: right hand rule around a loop
  • magnetic field lines: B field
  • Right hand rule: F= qvB(sin theta)
  • more complex: cyclotron formula


Magnetism discussion questions

  1. Explain why sailors used magnetic compasses while the Arab voyagers did not. Hint: one travels on the desert.
  2. Look up the various ways modern airlines navigate. Why do they use one and not the other?
  3. Explain why we don’t see the Aurora Borealis in Hawaii, except when there is severe solar weather.
  4. Use the stream analogy to explain magnetic field lines.


Physics Final review

Download file "physics exams toto.pdf"


Waves and sound lab

We will have several days to complete this lab, so don't panic. You may do these segments in any order, in groups of two or less (no mega-groups).

Speed of sound:
  • Using the water tubes, measure the resonant length for three different frequency tuning forks.
  • Calculate the speed of sound for each
  • Average these
  • Question: what would happen to the wavelength if the temperature rose?
Standing waves:
  • Using the slender springs, create a standing wave a few meters apart. Notice the frequency.
  • Send a pulse along this stretched spring and measure the time it takes to travel from one end out and back. Calculate the velocity of the pulse.
  • Using this velocity and the distance apart, predict the frequency you would need to shake the end to create a single standing wave.
  • Repeat this for a double standing wave.
  • Question: Otis is sitting on a dock in the bay (ha ha ha). He notices waves that are 10 meters apart. If these waves are traveling at 2 m/s, what is their frequency?
Transverse and longitudinal waves:
  • Using the slinky, create a longitudinal wave pulse. Notice the time it takes to reach the other end.
  • Calculate the longitudinal velocity of this wave.
  • Using the same slinky, the same distance apart, calculate the velocity of a transverse wave.
  • Are these similar or different?
  • Question: longitudinal waves can go through solids or liquids. Transverse waves can only go through solids (ocean waves are a different case). Look up seismology online and find out how scientists know that parts of the earth are solid and others liquid.



Our study of waves will involve the following worksheets created by Mr. Bleckel:
Download file "Waves2017.pdf"

Download file "waves2 2017.pdf"

Download file "Introtowaves.pdf"

We'll go over these in class Tuesday 4.18.17, and will use class time Thursday and Friday to work on the labs

Email me if you have any questions


Astro questions 4.9.13

Please email me your responses by Sunday night:

1. Explain the limitations of using parallax to determine star distances
2. Use three star names in arabic to illustrate why so many star names are in arabic. Explain why this is so.
3. Using red shift, explain why we know how old the universe probably is
4. Explain the first few seconds of the big bang, and why this is bringing physicists and astronomers together in the same quest.
5. What tools are physicists using to explore this?
6. How were telephone engineers instrumental in determining the age of the universe?
7. How did retrograde rotation explain the rotation of the planets?
8. How does the main sequence help us find the age of stars and their temperature?
9. If we know the temperature of a star, how can we find "Goldilocks" planets?
10. Explain how Keck has been so good at finding exoplanets.

let me know how I can help.


Honors physics astro notes

tyco brahe
goldilocks planets
ships with no sea
hoku ula


Lab: Electrical equivalent of heat

We use electricity to heat water many times in our lives: cooking, cleaning, bathing and so on. How efficient are these heating methods? That's what you are going to determine, using two methods: a hot plate and a microwave oven.

The Hot Plate part:
Measure a certain amount of water ( 200 mL) in a beaker and put on the hotplate.
Put a temp sensor in the water and measure temp for a few minutes to stabilize the temperature.
Once you are confident it has equilibrated, plug the hot plate into a Kill-a-watt unit, which is plugged into the 120Volt outlet.
Turn on the hotplate, and start recording the temperature. A good interval might be every few seconds for at least 2 minutes.
Calculate the slope of the graph, including the units.

Stuff you need to know:
The amount of energy needed to change the temperature is:
Q = mc∆T
Q = energy in Joules
m = mass of water in grams (1 ml = 1 cc = 1 cm2 = 1 gram for water)
c = specific heat of water = 4.18 J/g ˚C
∆T = temperature change in °C

From the Kill-a-watt unit
  • What was the power reading on the hot plate while you were heating the water? This is usually measured in Watts, or joules/sec

From the data:
  • What was the measured slope of the graph, in what units?
  • At what rate was the electrical energy transformed into heat?
  • Calculate the efficiency of the hot plate.
The Microwave part:
Measure about 200 grams of water in a glass beaker.
Using a temp sensor, record the temperature of the water, as you did above.
Plug the microwave into a kill-a-watt unit
Set the microwave oven to 50% power.
Heat the water for two minutes.
Measure the change in temperature, record.

  • What was the change in temperature for the water?
  • How much energy was absorbed by the water?
  • How many seconds did the microwave heat the water?
  • How many Watts were used by the microwave oven?
  • Multiply the Watts x seconds, this should be the number of joules
  • How efficient is the hot plate?

1. List at least three ways energy is lost in the microwave heating
2. what are three reasons not to use a microwave to cook with
3. How would you make the hot plate more efficient?
4. What makes the hot plate so inefficient?
5. About how much energy is wasted in cooking in our country?


Honor Physics Astro 1.0

We're now moving into the part of your Honors Physics course I've been looking forward to: the study of Astronomy and Astrophysics. What's the difference you ask? That's one of your first questions.
I'll post questions here each week, which will be due the Sunday before we have meetings on Tuesday morning. Why Sunday? It gives me a chance to read your responses and give you feedback before we discuss in our Tuesday meetings.
Here's how we'll start:
Using Wikipedia, look up each of the following, and explain in your own words. Include the following:
a. how recently was this discovered
b. where is research on this most active now
c. why is this relevant to your life
d. what parts of what you have learned in physics are useful in understanding these

The topics:
sideral time
age of the universe
heat death of the universe
background radiation from the big bang
the big bang
optical telescope
radio telescopes
black hole
red giant
neutron star
main sequence
white dwarf
brown dwarf

Please email my your responses by March 24, the Sunday before classes resume.
Let me know if you have any questions.


Semester video projects

Physics Semester video project




vectors and scalars

average velocity

position time graphs


velocity-time graphs



two dimensional motion

projectile motion



action= reaction






Spring energy

Work-energy theorem




circular motion

centripetal force





Welcome to Physics!
Here's your syllabus
Download file "Physics syllabus 2013_gm.docx"

Welcome to Physics/Physics Honors


Jerry Bleckel, Greg McKenna, Dr. Bill Wiecking,,,

The Course

Physics is an introductory survey course that covers everything in a traditional high school physics course. This year, we will study motion, forces, energy, matter, waves, electricity, magnetism and modern physics.


Active Physics by Eksenkraft, Third edition. Publisher: It’s About Time, Herff Jones Education Division. The text can be found as a .pdf file at We will supplement this textbook with the excellent online site and other videos that can be found on We will likely use this often to supplement the lectures in class.

What you’ll need to bring to class

scientific calculator other than your phone/tablet

3-ring binder for taking notes, storing handouts, etc. with lined paper

straightedge, colored pencils, other tools.

Classroom Procedures

1. On the way into class, pick up the daily worksheet at the desk nearest the door.

2. All cell phones and electronic devices need to be shut off and put away.

3. When the class begins, students are to be in their seats with their homework on the desk space in front of them. We will go over questions about the homework as well as any questions about the lectures.

4. During group work, students are expected to talk quietly with members of their own group.

5. When help is needed during a test, during seatwork, or during group work, students are to raise their hands for teacher assistance. While waiting, students should continue to try to answer the question on their own.

6. Tardy students must drop their tardy note on the desk as they enter.

7. When absent, students are expected to do the assignments in the syllabus except in unusual cases. It is expected that you will write or call me in such circumstances.

8. Questions of a personal nature, such as questions about points given for a particular assignment, should be brought up individually with the instructor before or after class.

9. If you lose handouts and other papers from class, it is your responsibility to make copies from other students. Papers from recent classes can usually be found in a folder by the door.


On, you can find your grades, assignments, and quizzes. We will register for this the first day of school. Your parents will have the opportunity to access Engrade as well.

Grades and Exams

There will be “evening quizzes” each day there is homework. You can find the quizzes in your Engrade account. Check the calendar each day. They will be short, usually 3 multiple-choice questions.

We will have daily quizzes, usually at the end of each class period. These daily quizzes will be short and review the work done during the class period. The daily quizzes will first be scored using the following table:



C Complete

J Justified

E Small errors

P partially justified

I Incorrect

N Not justified

Once the daily quizzes are returned, you will have the task of correcting and explaining your mistakes for each problem. (If you receive a score of C/J no correction will be necessary). You will then give yourself a grade for the quiz and return it. I will either agree or disagree with your grade, and enter it in the Engrade grade book. Note: Daily quizzes may also be on the lab investigations. Students may NOT re-take quizzes. Be ready each day.

Formal Labs

You will most likely do one formal lab write-up each quarter, possibly two. They will be graded in the Correctness/Process format above.


Tests will be given at the end of each unit. Our tests will be based on practice problems that you will already have had a chance to master.

Grading Percentages

Evening quizzes 10%

Daily quizzes (including lab investigations) 10%

Labs (investigations) 10%

Lab formal write-ups 20%


Homework/Class Work

We’ll be trying something new this year. Your homework will mostly consist of watching short videos on and doing a few “easy” questions as well as a complex question or two (once we are able). In class, we will review these videos, practice solving problems and/or do lab investigations. The Engrade homework/quizzes will be CLOSED by 8:30 a.m. the day of class to enable the instructor to view the results prior to class.


As you may have noticed, our class is called “Physics/Physics Honors.” All five sections of the course will be treated the same. If you desire to take the challenge of Physics Honors, you will be required to design, create, and execute a science fair project in the fall and winter. In the spring, once the science fair is complete, we will move to another project, most likely astronomy. We will be meeting every Tuesday from 8 – 8:30 a.m. in room 41a. Our first meeting is August 28 in room 41a.

Emergency Procedures

In the event of an emergency, exit the room via either door and gather as a class at the bottom of the hill. Remain quiet and await further instructions.

Final Note

Messrs. Bleckel, McKenna, and Wiecking are all available to help any student, even if they are not your primary teacher.