Re: If E= I*R, then what's a good experiment to check it out & learn hands on?

Di,

A simple experiment to verify Ohm's Law requires some resistors, 
batteries, and a multi-meter.

The multi-meter will allow you to measure the resistance of your 
resistors, the voltage at various points in your circuit, and the current 
in your circuit.  Use a 9V battery and get resistors that are around 
50Kohms (47Kohms is common, 10Kohms or 100Kohms would be fine also).  The 
voltage and current levels are all very safe.  Be careful not to leave the 
circuit hooked up for a long time because it could drain the battery.  If 
your battery gets weak, the measurements you make may not make sense.  You 
should be able to make all of the circuits by twisting wires together.  
You don't need to do any soldering.

I would suggest building the following circuits and making the following 
measurements:

1)  Build a series circuit.  This is done by connect the leg of one 
resistor to the leg of the other resistor and the two "free" legs to the 
plus and minus terminals of the battery.

Measure the individual resistances, R1 and R2, with the ohmmeter setting 
of your multimeter.  Then measure the total resistance.  Verify that it 
equals. R1 + R2.  

Attach the battery and measure the voltage across both resistors (total 
voltage), and the voltage across each of the resistors (V1 and V2).  How 
are the voltages related?

Predict the amount of current you expect to see in the circuit using Ohm's 
Law.  Wire the multi-meter in series into your circuit and measure the 
actual current.  How close does your measurement agree.  Wire your multi-
meter into another position in your circuit.  Is the current at this point 
the same or different from the previous point?

NOTE:  Do not measure across the terminals of your battery with the multi-
meter in the ammeter setting.  This could damage the meter.


2)  Build a parallel circuit.  This is done by connecting the legs of the 
resistors together and then have both sets connected across the battery.

Again, measure the individual resistances and total resistance (RT).  In 
this case, you should find the following:

  1      1      1
---- = ---- + ----
 RT     R1      R2 

Measure the voltage across the total circuit and each of the resistors.  
How are these voltages related?  

Using Ohm's Law, predict total current, and the current in each of the 
resistors.

Measure the current in the total circuit and in each of the resistors.  
How are these currents related?  How do they compare to your predictions?

One of these circuits is a Current Divider, and the other is a Voltage 
Divider.  Can you determine which is which and why?


Please contact me if you have any questions, or if the above isn't clear.

Chris Seaman
Alcoa Technical Center
christopher.seaman@alcoa.com