Looking for constructive crit.

russrmartin · Dec 14, 2005

Hey guys. I have an interview at a Technical College in which I need to to a 15 presentation on a subject of my choice. Sort of an "how I would teach" if you will. I chose to use Ohms Law for it's simplicity. I have prepared a Powerpoint for a visual aid and was hoping some of you would give it a look and see if there is anything in it that is irrelevant, or should be included. Please try to view this with the mindset you had when you were first learning this, would you find anything confusing, etc. Thanks in advance for your input.

Russ

Alan Case · Dec 14, 2005

The volts, ohms and resistance definitions could be a bit hard to follow if you are teaching to people straight off the street.
I saw a good analogy of water pressure as the voltage, resistance as the size of the hose and current as the litres flowing out the hose.
Makes it easy to explain to beginners.
Regards Alan Case

russrmartin · Dec 14, 2005

Thanks Alan. Now that you brought that up, I remember my instructor actually using the same analogy, and it does work well. I will incorporate it into my powerpoint. Thanks.

Russ

gas · Dec 14, 2005

When I have had students that couldn't quite grasp what Ohm had to say I used the hose thing. It seems like everyone has experienced pressure drop from a long garden hose.

keithkyll · Dec 14, 2005

In your heater example, that would need to be 240 volts DC. Use automotive circuits as a better example, or a flashlight.
Show the 2 circle charts E/IR and P/IE. Show how you cover up the unknown value to "see" the equation needed.

Get in depth with a real world example:
What happens when the ground opens on a car's tailight?
Why does a fuse blow?
Calculate how long a battery will last (amp-hour rating)

Keith

Lancie1 · Dec 14, 2005

Good point Keith. Actually the basic formula works for single phase AC also, but not 3-phase AC.

The waterflow-to-current flow comparison must be older than Moses! It is a necessary nugget of knowledge for electrical instructors.

russrmartin · Dec 15, 2005

All good suggestions. I will try and update the PP and post the results sometime tomorrow. Thanks again.

Russ

SimonGoldsworthy · Dec 15, 2005

The heater example may cause some debate as ohms law is only valid if the temperature coefficient of the material is zero. In a heater the resistance will be different when cold and hot. Just a note in case someone decided to take some practical measurements and question the results.

As you are using power point, you could also incorporate a picture of a circuit showing a battery, voltmeter, ammeter and resistor showing where they are inserted and what they are reading.

The basic definition of ohms law is as follows:

Ohm determined that the current that flows through a wire is proportional to its cross sectional area and inversely proportional to its length

and it is from this that the I=V/R formula was derived. Just some more background information in case you are quizzed by the interview board.

keithkyll · Dec 15, 2005

The way I was taught: "It takes one Volt of Electromotive force to pass one Ampere of current through one Ohm of resistance".
I think Mr. Volta and Mr. Ampere were part of this too?

gbradley · Dec 15, 2005

I always liked the Ohms law circle.

Looks like you've got a nice start.
Good luck!

Leadfoot · Dec 15, 2005

Looks right nice.

Remember at this point you are not trying to "cause learning to happen". You are just demonstrating your ability to attempt to make it happen.

Any time you can use something that the students are familiar with to associate works really well. I always try to do that.

Jiri Toman · Dec 15, 2005

Actually the basic formula works for single phase AC also

Ohms law does not work for AC currents because it does not take into account reactance which is always present in AC circuits.
Derivative of Ohms called general law is used instead.

TimothyMoulder · Dec 15, 2005

An example my teacher gave was pushing a stalled car.

Voltage = how hard you push
Resistance = road condition (uphill, flat, downhill)
Current = how fast the car moves.

Pushing uphill will require more force to generate the same speed than you would need on a flat, and downhill would require less.

One of those universal experiences we've all had at some point...

TM

rsdoran · Dec 15, 2005

I will go with Lancie on this, Ohms law basically applies the same to single phase AC ckts. Technically a resistive load will only "see" AC which is equivalent to DC (RMS)...ie 120vac = 120vdc in a resistive ckt.

It can get more involved than that but a minor change to the formula; For an AC circuit Ohm's law can be written V = I * Z, where V and I are the oscillating phasor voltage and current respectively and Z is the complex impedance for the frequency of oscillation.

Ohm and Kirchoff still apply to basic AC ckts;
http://www.patchn.com/AC/AC_1.html

I am not familiar with "Derivative of Ohms called general law" so could you provide more information on the subject please. I always thought complex numbers (vectors etc) were used in AC ckts.

Jiri Toman · Dec 15, 2005

Ron,

You have actually stated the general law. You are right if you have purely resistive load the ohms law still applies to AC, however there is no such thing as 100% pure resistive load, capacitance and
reactance will be present even if infinitesimal.
Complex numbers or j-notation (j = square root of -1) are used
to calculate Z. Seeing that you are a full time engineering student now, I suggest that you learn that really well. Circuit analysis
classes require knowledge of complex numbers.
Understanding differences in what reactive impedance and capacitive impedance do in terms of phase shifting of current/ voltage is one thing that many people get confused about.

Looking for constructive crit.

russrmartin

Member

Alan Case

Lifetime Supporting Member

russrmartin

Member

gas

Member

keithkyll

Member

Lancie1

Lifetime Supporting Member

russrmartin

Member

SimonGoldsworthy

Member

keithkyll

Member

gbradley

Lifetime Supporting Member

Leadfoot

Member

Jiri Toman

Member

TimothyMoulder

Member

rsdoran

Lifetime Supporting Member

Jiri Toman

Member

Similar Topics