Discover: Resisting My Circuit

Resistors can be useful in electric devices.


Conductors, insulators, and resistors are used for building electrical devices and the circuits that control them. For example, think about a simple desk lamp. The lamp has an insulated plastic cord to protect the user from short circuits.  The lamp has wires that conduct electricity from the lamp to wires that lead to a switch that might be located on the wall. When the lamp is switched on, the bulb acts as a resistor in the circuit. It takes some of the current and turns it into light. 

Resistors have a special place in electrical circuits because they allow the user to control the amount of current.  Every electronic device has resistors.  


Resistors
  • protect people from high voltage shocks 
  • protect devices such as lamps from being damaged by large currents 
  • lower the voltage  
  • convert electricity into another form of energy (heat or light)

One example of a good resistor is graphite. It allows current to flow, but it cannot flow well. If electricity has to travel through a graphite resistor, the current is reduced.

What happens when we add a resistor to a circuit?

Materials
  • Electricity Kit Items: 1 connecting wire, AA battery holder, lightbulb, lightbulb holder
  • Not included in Electricity Kit:
    2 AA batteries, tape, piece of paper, thick rubber band, ruler, #2 pencil

  Video

Watch Paper Circuit! The graphite in pencils is an adequate conductor to allow you to build circuits by drawing on paper!
Pencil Graphite as a Variable Resistor


  Notebook

Click on the icon to download the instructions for this activity. Save to your Electricity Notebook.

  Check Your Answers

Once you have completed this activity, check your answers below. 

Graphite Resistor Observation Chart

 Placement of Connecting Wires What Did You See?
Connecting wires far apart on pencil rectangle
The bulb (or LED) glows dimly.
Connecting wires close together on pencil rectangle
The bulb (or LED) glows brightly.
Connecting wires moved slowly back and forth on pencil rectangle
The bulb (or LED) alternates between glowing dimly and glowing brightly.

Explanation

The graphite from the pencil is a resistor.  It conducts electricity, but it does that poorly.  When electricity must travel through more graphite, it meets with more resistance and less electricity flows, making the light dimmer.