1. Electric Circuits 22-3

2. Controlling the Current Imagine a bucket with a hose at the bottom. If the bucket is raised, water will flow out of the hose faster than before. Increasing the height will increase the current.

3. Voltage and Resistance If the diameter of the tube is decreased, resistance is greater and the flow of the water decreases. In the same way, as the resistance in an electric circuit increases, the current in the circuit decreases.

4. Ohm’s Law A nineteenth-century German physicist, Georg Simon Ohm, carried out experiments that measured how changing the voltage in a circuit affected the current. He found a simple relationship among voltage, current, and resistance in a circuit that is now known as Ohm’s law.

5. Ohm’s Law According to Ohm’s law, when the voltage in a circuit increases the current increases. However, if the voltage in the circuit doesn’t change, then the current in the circuit decreases when the resistance is increased.

6. Series and Parallel Circuits For current to flow, the circuit must provide an unbroken path for current to follow. There are two kinds of basic circuits—series and parallel.

7. Wired in a Line A series circuit is a circuit that has only one path for the electric current to follow.

8. Branched Wiring Houses, schools, and other buildings are wired using parallel circuits. A parallel circuit is a circuit that has more than one path for the electric current to follow. If one path is broken, electrons continue to flow through the other paths.

9. Protecting Electric Circuits When the current becomes larger than 15 A or 20 A, a piece of metal in the fuse melts or a switch in the circuit breaker opens, stopping the current. To keep the wire from becoming hot enough to cause a fire, the circuits in houses and other buildings have fuses or circuit breakers.

10. Electric Power The rate at which electrical energy is converted into other forms of energy is electric power. In an electric appliance or in any electric circuit, the electric power that is used can be calculated from the electric power equation:

11. Electric Power The electric power is equal to the voltage provided to the appliance times the current that flows into the appliance. In the electric power equation, the SI unit of power is the watt.

12. Cost of Electric Energy Power is the rate at which energy is used, or the amount of energy that is used per second. Using electrical energy costs money.

13. Electrical Safety Electricity can have dangerous effects. In 1997, electric shocks killed an estimated 490 people in the United States.

14. Electric Shock A current can enter your body when you accidentally become part of an electric circuit. Whether you receive a deadly shock depends on the amount of current that flows into your body.

15. Lightning Safety If you cannot go indoors, you should take these precautions: ∙ Avoid high places and open fields. ∙ Stay away from tall objects such as trees, flag poles, or light towers.