This excercise will help you determine **the relationship between voltage (V), amperage (I) and resistance (R)**. This relationship is called *Ohm's Law*

This experiment consists of modifying a circuit. The circuit is made up of four parts:

- a battery that outputs an amount of energy. This energy is called
*voltage*(**V**) and the unit of measurement is called*volts*. - a wire, which has
*resistance*(**R**). Resistance inhibits the amount of current running along the circuit. The greater the resistance, the lower the current. - a lightbulb which has an
*amperage*(**I**). The amperage of the lightbulb tells us how much energy the lightbulb requires to function. - a switch, which turns the system on and off.

The problem consists of two parts:

- Find the formula which describes Ohm's Law; that is, find the mathematical relationship between voltage (
**V**), amperage (**I**), and resistance (**R**). - Determine the amperage of the lightbulb.

The first part will be discovered through a trial-and-error experiment. You are given a circuit on which you may vary the voltage by choosing from a variety of batterys and the resistance by adding resistors to the circuit. You will then turn on the switch, allowing current to flow through the circuit. If the resistance is too low, the lightbulb will receive too much energy, and will explode. If the resistance is too great, the lightbulb will not receive enough energy, and will not light. If the resistance is just right, the lightbulb will light up.

If the lightbulb explodes or fails to light, turn off the switch (which automatically replaces the lightbulb) and try again.

First, concentrate on changing the resistance to get the lightbulb to turn on. Once you get a working circuit write down your values, change the value of the battery, and try again. You should begin to see the relationship between **V**, **I**, and **A**. You should then be able to derive what the Amperage of the lightbulb is.

Each battery and resistor has a value printed on it which reflects the objects voltage and resistance, respectively.

- To add batterys to the circuit, use the mouse to drag a battery from the toolbox (the box containing the various resistors and batterys) and drop it onto the larger battery on the circuit.
- To add resistors to the circuit, drag a resistor from the toolbox onto the empty box located on the circuit. Multiple resistors may be added to the circuit.
- To remove resistors, simply drag the resistor you wish to remove from the circuit and drop it anywhere outside of the resistor box.
- To turn the circuit on and off, click once on the switch.

Now that you know Ohm's law, you can apply it to a circuit where all values are known.

In this next circuit, the lightbulb has a different amperage than in the previous experiment. Furthermore, we will tell you what the amperage of the lightbulb is. Given this information, you should be able to complete the circuit correctly with one try.

Sean Russell ser@cs.uoregon.edu The source for the Java applet can be found here

Graphic images by Amy Hulse