1. Chapter 20, Section 4 Electrical Safety Wednesday, January 20, 2010 Pages 666 -- 670

2. Objectives Identify the safety devices used to protect people from common electrical hazards. Describe how a lightning rod protects a building. Explain how the severity of an electric shock is related to current, voltage, and resistance.

3. Vocabulary Words Short circuit Third prong Grounded Lightning rod Fuse Circuit breaker

4. Becoming Part of a Circuit Short circuit is a connection that allows current to take an unintended path.  The unintended path in a short circuit offers less resistance than the intended path.  The current is high.  Potentially cause a fatal electric shock.

6. Exposed Wires An exposed wire is when the protective insulation around the wire wears off. Dangerous because current flows when there is voltage.

7. Resisting Current The soles of your shoes will normally provide a large resistance between your feet and the surface of Earth.  Result is the current would not be strong enough to cause serious injury.

8. Grounding Provides protection against shock.  Can be through grounding wires.  Current will go directly into Earth through a low-resistance grounding wire.

9. Third Prong Connects the metal shell of an appliance to the ground wire of a building.  A circuit is electrically grounded when charges are able to flow directly from the circuit into the ground connection in the event of a short circuit.

10. Lightning Rods A metal rod mounted on a roof of a building in order to protect it.  Connected to a grounding wire.  When lightning strikes the rod, charges flow through the rod, into the wire, and then into Earth.

11. Fuses and Circuit Breakers Fuses and circuit breakers are devices added to circuits.  Prevents circuits from overheating.

12. Fuses A device that contains a thin strip of metal that will melt if too much current flows through it.  Circuit is broken when the metal melts.  The flow of current is stopped.  A burned out fuse cannot be used again.

13. Circuit Breaker Safety device that uses an electromagnet to shut off the circuit when the current gets too high.

14. Electric Shocks The human body depends on electrical signals. Electrical pulses control certain functions in the human body. Electric currents from outside sources will interefere with the normal processes within your body.

15. Current in the Body Severity of the electric shock depends on the current. A current of less than 0.01 amp is almost unnoticeable. A current between 0.1 amp and 0.2 amp can be dangerous.

16. Resistance in the Body The current of an electric shock is related to voltage and resistance. The voltage is determined by the source of the shock. Resistance in the human body affected by many factors.  Conducting ability of body tissue.  Whether the skin is wet or dry.

17. Homework Workbook 20.4 (due 1/22) Worksheet 20.4 (due 1/22) Vocabulary quiz 20.4 (1/22)