Electricity & Magnetism: Pencil Lead Stripe

PIRA Class: 5D15.12

Purpose:  

To qualitatively demonstrate how a conductor's resistance is proportional to its length.  

Description: 

A pencil lead and its drawn line are part of a simple circuit. As the line is drawn longer and longer, the resistance of this circuit is observed to increase, or alternately the current is observed to decrease.

1. Connect a 6 volt battery to a thickly drawn line (~3 cm. long), and use a multimeter to measure resistance of the line.

2. Extend the length of the line while observing the change in the circuit's resistance.

ALTERNATES:

- To demonstrate a conductor's width and resistance inverse proportionality, double the thickness of the line and the resistance will decrease.

- Draw (curved) lines side by side to demonstrate how parallel circuits will generally have decreased resistance.

NOTE: The thickness and width of these hand drawn lines is difficult to control. Do not expect multimeter readings that can quantitatively compared. 

Equipment: 

Graphite pencil, paper, multimeter

Location:

Shelf 514