Chapter 20, Section 4Electrical Safety

Wednesday, January 20, 2010

Pages 666 -- 670

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.

Vocabulary Words

Short circuitThird prongGroundedLightning rodFuseCircuit breaker

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.

Exposed Wires

An exposed wire is when the protective insulation around the wire wears off.

Dangerous because current flows when there is voltage.

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.

Grounding

Provides protection against shock. Can be through

grounding wires. Current will go directly

into Earth through a low-resistance grounding wire.

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.

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.

Fuses and Circuit Breakers

Fuses and circuit breakers are devices added to circuits. Prevents circuits from

overheating.

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.

Circuit Breaker

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

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.

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.

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.

Homework

Workbook 20.4 (due 1/22)Worksheet 20.4 (due 1/22)Vocabulary quiz 20.4 (1/22)