Lecture Demonstrations Laboratory

The Demonstrations Manual

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Electrostatics
Electric Fields And Potential
Capacitance
Current and Resistance
Electromotive Force And Current
DC Circuits: Ohm's Law; Resistivity of a Pencil; Resistive Heating of Nichrome Wire; Blowing a Fuse; Wheatstone Bridge; Wheatstone Bridge II; Circuit Analysis; RC Circuit; RC Time Constant (DECAY); Telephone model as simple DC circuit
Magnetic Materials
Magnetism
Inductance
Induction
Complex Circuits
Semiconductors And Tubes
Transmission Lines and Antennas

Resistivity of a Pencil

Purpose:

To show that the resistance of a piece of material (in this case graphite) is proportional to its length.

Procedure:

Connect the bulb, battery and pencil in series. The bulb can be dimmed or brightened by sliding one of the connectors along the exposed graphite of the pencil.

Comments:

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Equipment:

Light Bulb
D battery
leads
Pencil