http://www.ck12.org Chapter 5. Energy
5.68 Electric Resistance
- Define resistance and identify the SI unit for resistance.
- List factors that affect resistance.
- Explain why resistance can be a help or a hindrance.
These athletes are playing rugby, a game that is similar to American football. The players in red and blue are trying
to stop the player in blue and black from running across the field with the ball. They are resisting his forward motion.
This example of resistance in rugby is a little like resistance in physics.
What Is Resistance?
In physics,resistanceis opposition to the flow of electric charges in an electric current as it travels through matter.
The SI unit for resistance is the ohm. Resistance occurs because moving electrons in current bump into atoms of
matter. Resistance reduces the amount of electrical energy that is transferred through matter. That’s because some
of the electrical energy is absorbed by the atoms and changed to other forms of energy, such as heat. You can see
an animation of resistance at the level of atoms and electrons at this URL: http://www.physics.org/explorelink.asp?i
d=1738&q=electricalresistance¤tpage=1&age=0&knowledge=0&item=3
Q:In the rugby analogy to resistance in physics, what do the players on each team represent?
A:The player on the blue and black team represents a moving electron in an electric current. The players on the red
and blue team represent particles of matter through which the current is flowing.
Factors That Affect Resistance
How much resistance a material has depends on several factors: the type of material, its width, its length, and its
temperature.