Resistors

• EM8.1 Measurement of Body Resistance

Connect a 1.5 V battery, a 4.7k resistor, a micro-meter, and a volunteer in series with each other. The volunteer is connected by means of holding two metals beakers connected to the circuit. Comparisons between the short circuit, the beakers held lightly, the beakers held tightly, and the volunteer's hands placed in the beakers filled with water.

NOTE: THIS WILL BECOME DANGEROUS WHEN THE CURRENT EXCEEDS 100mA.

• EM8.2 Physical Representation

This is a board with nails arranged in such a manner that when marbles are released at the top (when the board is tilted) they keep hitting a nail and having to change their direction of travel. This is a physical representation of electrons drifting through a medium and the resistance it encounters.

• EM8.3 Potentiometers

Connect the potentiometer, transformer and meter in series. Varying the D42 potentiometer will change the current.

• EM8.4 Resistance Dependence on Temperature

A power transformer is attached to one end of the exposed wire. The other is connected to the big demonstration meter, and that is finally attached to the transformer. Turn the power on and let the class see the current through the wire. Place the fan new the wire and turn it on. As the wire cools, the current increases.

Be careful not to put too much current through the coil as to not melt the coil or its plexiglass holder, for that will result in a rather unpleasant odor for the remainder of the class.

• EM8.5 Resistance of Light Bulbs

A variable DC power supply is connected in series with a light bulb and an ammeter. Varying the supply will change the current. Measuring the voltage across the light bulb by attaching a voltmeter in parallel with the light bulb, the resistance of the light bulb can be determined.

• EM8.6 Series/Parallel Circuit

Series/Parallel circuit is designed for use with a 10 Volt power supply or the Hand-Crank Generator. The two light bulbs can be wired in series or in parallel. The two knife switches enable students to switch on one bulb or both bulbs. Use with overhead document camera.