unit 4 ch 20.3 ppt

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Unit 4 Ch 20.3 Ppt Electricity

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Unit 4 Ch 20.3 Ppt. Electricity. Electricity Electric Charge 1. Static electricity is the accumulation of excess electric charges on an object. a. More electrons = - negative charge b. More protons = + charge. 3. Law of Charges. a. Opposite charges attract. - PowerPoint PPT Presentation

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Page 1: Unit  4  Ch  20.3  Ppt

Unit 4 Ch 20.3 Ppt

Electricity

Page 2: Unit  4  Ch  20.3  Ppt

ElectricityA.Electric ChargeB.1. Static electricity is the

accumulation of excess electric charges on an object.

a. More electrons = - negative charge

b. More protons = + charge

Page 3: Unit  4  Ch  20.3  Ppt

3. Law of Charges a. Opposite charges attract. b. Like charges repel.4. Electric fields

a. Electric fields exert force on objects within the field. b. Weaker with distance.

Page 4: Unit  4  Ch  20.3  Ppt

5. Transferring electric charge a. Conductors: e¯ move easily. b. Insulators: hold e¯ tightly. c. Contact charging is done when two materials are rubbed together (best with insulators). d. Charging by induction is done when one charged object induces a charge on another.

Page 5: Unit  4  Ch  20.3  Ppt

6. Lightning a. Large static discharge between the earth and clouds. b. Lightning was found to be static electricity by Ben Franklin.7. Grounding a. Conductive path to Earth. b. Lightning rods & plumbing.

Page 6: Unit  4  Ch  20.3  Ppt

8. The electroscope can be used to detect electric charge

Page 7: Unit  4  Ch  20.3  Ppt

B. Electric Current1. The reason electric charge flows from one place to another is voltage.HIGH

LOW

a. Voltage is the difference in electrical potential between two places where e¯ are flowing. b. Voltage is the “push” that makes electric charges move. c. Measured in volts (V).

Page 8: Unit  4  Ch  20.3  Ppt

2. The flow of electric charge is called current. a. Current is measured in amperes, or amps (A). b. Voltage causes current.3. The amount of electric charge is measured in coulombs. a. 1 coulomb is the charge carried by 6.24 x 10^18 e¯. b. 1 amp is 1 coulomb per sec.

Page 9: Unit  4  Ch  20.3  Ppt

4. Batteries are e¯ pumps. a. They provide a voltage difference to a circuit. b. Types: wet-cells & dry-cells

Page 10: Unit  4  Ch  20.3  Ppt

5. Resistance a. Opposition to the flow of e¯. b. It changes electrical energy into thermal energy and/or light. c. Measured in ohms. d. Conductors have less resistance than insulators.

Page 11: Unit  4  Ch  20.3  Ppt

e. Wire resistance greater for: 1) Longer wires 2) Thinner wires 3) Higher temperatures

Page 12: Unit  4  Ch  20.3  Ppt

6. Ohm’s law

Voltage Difference Current = Resistance

I

V

R

Page 13: Unit  4  Ch  20.3  Ppt

C. Electrical Circuits1. A circuit is a conducting path.2. Series circuit a. One path b. Any break & all devices go out c. Current is the same throughout the circuit

Page 14: Unit  4  Ch  20.3  Ppt

3. Parallel circuit a. Multiple paths b. A break in one branch & the other branches stay on c. Voltage is the same in each branch, but current and resistance may be different

Page 15: Unit  4  Ch  20.3  Ppt

Comparison of series and parallel circuits

The same voltage battery

Notice the brightness of

the bulbs

Page 16: Unit  4  Ch  20.3  Ppt

4. Household circuits

a. Mostly parallel. b. 120 V in the U.S. c. More devices plugged in a circuit mean more current. d. More current means more heat in the wiring.

Page 17: Unit  4  Ch  20.3  Ppt

5. Electrical safety devices

a. Fuses - one time use. b. Circuit breakers - can be reset and reused.

Page 18: Unit  4  Ch  20.3  Ppt

D. Electric Power and Energy 1. Electrical power is the rate at which electricity is converted into another form of energy. a. Power = current x voltage b. Unit is the watt or kilowatt. 2. Electrical energy a. Energy = power x time b. Unit is the kilowatt-hour. (1000 watts for 1 hour) c. This is what we buy from the electric company.

Page 19: Unit  4  Ch  20.3  Ppt

E. Light Bulbs

1. Incandescent a. Have a tiny filament that resists the flow of electrons. b. The filament gets hot and glows to produce light. c. Very hot and inefficient.

Page 20: Unit  4  Ch  20.3  Ppt

2. Fluorescent

making it give off U-V rays. c. Phosphor absorbs U-V rays and glows to make light. d. Very cool, efficient, and last a long time.

a. Filled with gas and coated with phosphor. b. Electricity excites the gas