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Section 1 Electric Charge and Static Electricity

Law of Electric Charge

• Charges Exert Force Atoms are composed of particles with electric charge. The law of

electric charges states that like charges repel and opposite charges attract.

Chapter 17




Chapter 17




Charge It!

• Friction Charging by friction happens when electrons are “wiped” from one object onto

another.

• Conduction Charging by conduction happens when electrons move from one object to

another by direct contact.

• Induction Charging by induction happens when charges in an uncharged metal object are

rearranged without direct contact with a charged object.

Chapter 17




Charge It!, continued

Chapter 17



Charging by Contact

Chapter 17

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Visual Concept





Static Electricity

Chapter 17

• Static electricity is the electric charge at rest on an object.

• Electric Discharge static electricity as charges move off an object. Ex: Include touching

a doorknob after walking on carpet. One of the most dramatic examples of electric

discharge is lightning.




Chapter 17



Section 2 Electric Current and Electrical Energy

Electric Current

• The rate at which charges pass through a given point. Measured amperes, or amps (A)

Chapter 17

• The amount of energy released as a charge moves between two points in the path of a

current. Measured in Volts (V)

Voltage




Voltage, continued

• Voltage and Electric Current As long as there

is a voltage between two points on a wire,

charges will flow in the wire. The size of the

current depends on the voltage.

• Varying Nature of Voltage Different devices

need different levels of voltage.

Chapter 17




Resistance

• Resistance is the opposition to the flow of electric charge.

• Resistance and Material Good conductors, such as copper, have low resistance. Poor

conductors, such as iron, have higher resistance.

Chapter 17




Generating Electrical Energy, continued

• Thermocouples Thermal energy can be

converted into electrical energy by a

thermocouple.

• Photocells A photocell converts light

energy into electrical energy.

Chapter 17



Section 3 Electrical Calculations

Connecting Current, Voltage, and Resistance

• Georg Ohm (1789 –1854) studied the resistances of materials. He measured the current

that resulted from different voltages applied to a piece of metal wire.

• Ohm’s Law Ohm found that the ratio of voltage to current is a constant for each material.

This ratio is the resistance of the material.

Chapter 17

R =V

I, or V = I R




Electric Power

• What Is Electric Power? The rate at which electrical energy is changed into other forms of

energy is electric power. Electric power is calculated using the following equation:

Chapter 17

• Watt: The Unit of Power The unit for power is the watt (W). Another common unit of

power is the kilowatt (kW). One kilowatt is equal to 1,000 W.

power = voltage current, or P = V I




Electric Power, continued

• Power Ratings When you read the wattage label

on a light bulb, you are reading the bulb’s power

rating. The power rating describes the rate at which

an electric device uses electrical energy.

Chapter 17




Measuring Electrical Energy

• The amount of electrical energy used in a home depends the power of the electrical

devices in the house and the length of the time that those devices are on. The equation

for electrical energy is as follows:

Chapter 17

electrical energy = power time, or E = P t




Measuring Electrical Energy, continued

• Measuring Household Energy Use Different amounts of electrical energy are used

each day in a home. Electric companies usually calculate electrical energy by multiplying

the power in kilowatts by the time in hours.

• How to Save Energy Every appliance uses energy. Replacing items that have high

power ratings with items that have lower ratings is a way to save energy.

Chapter 17



Parts of an Electric Circuit

• Forming a Loop An electric circuit is a complete, closed path through which electric

charges flow.

• All circuits need three basic parts: an energy source, wires, and a load.

Chapter 17 Section 4 Electric Circuits



Section 4 Electric CircuitsChapter 17



Parts of an Electric Circuit, continued

• A Switch to Control a Circuit Sometimes, a circuit also contains a switch. A switch is

used to open and close a circuit.




Types of Circuits

• Series Circuits A series circuit is a circuit in which all parts are connected in a single loop.

• Uses for Series Circuits Series circuits are useful in wiring burglar alarms. If any part of the

circuit fails, there will be no current in the system and the alarm will sound.




Types of Circuits, continued

• Parallel Circuits A parallel circuit is a circuit in which loads are connected side by side.

• Uses for Parallel Circuits Almost all appliances are built with parallel circuits so that they

will keep working if part of the system fails.




Household Circuit Safety

• Circuit Failure Broken wires or water can cause a short circuit. In a short circuit, charges

do not go through one or more loads in the circuit.

• Fuses A fuse has a thin strip of metal. Fuses keep charges from flowing if the current is too

high.




Household Circuit Safety, continued

• Circuit Breakers A circuit breaker is a switch that

automatically opens if the current is too high. Charges

stop flowing.

• Electrical Safety Tips Do not overload circuits by

plugging in too many electrical devices. Do not use

electrical devices near water.




Interpreting Graphics

Use the diagram below to answer the questions that follow.

Chapter 17 Standardized Test Preparation



1. Opening which switch will turn off only light bulb

2?

A switch 1

B switch 2

C switch 3

D switch 4




2. Opening which switch will turn off exactly

two light bulbs?

F switch 1

G switch 2

H switch 3

I switch 4




3. If only switches 2 and 3 are open, which of the

following will happen?

A All three bulbs will remain lit.

B Only bulb 1 will remain lit.

C Only bulb 3 will remain lit.

D All three bulbs will turn off.




4. Which of the following statements is false?

F Bulb 2 will be off when bulb 1 is off.

G Bulb 3 will be on if any other bulb is on.

H Bulbs 1 and 3 can be on when bulb 2 is

off.

I Bulb 3 can be on when bulbs 1 and 2 are

off.


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