### How Can You Resist?

Do you see the small blue and silver cylinder near the bottom of this mercury-vapor light bulb? It’s an electrical device called a resistor.

#### The Back Story

- A resistor is a device used to regulate the amount of electric current in a circuit. Resistors are used in light bulbs and appliances to limit the amount of current that reaches them. They work by resisting the flow of current through the circuit.
- Resistors come in different sizes. Which size does a device need? You can use Ohm’s law to find out.
- Ohm’s law states the relationship among voltage, current, and resistance in a simple electric circuit. For a better understanding of these relationships, experiment with this applet: http://www.physics.uoguelph.ca/phyjlh/Fendt/phe/ohmslaw.htm

#### Can You Apply It?

At the link below, learn more about Ohm’s law and how to use it. Then answer the questions that follow.

- State Ohm’s law and represent it with a formula.
- What SI units are used for the variables in the formula for resistance in question 1?
- How many ohms of resistance does a resistor need to provide for a 12-volt circuit to carry 6 amps of current?
- How much current does a 120-volt circuit carry if it contains a resistor that provides 10 ohms of resistance?
- What do you think might happen to an appliance in a circuit if the wrong resistor is used so the appliance gets too much current?