1. Chapter 20

2. I. Electric Charge
Electric charge – an electric property of matter that creates a force between objects

3. 1. opposites attract
2. like charges repel
3. conductors allow charge flow (insulators do not)

4. 3. Conductors allow charges flow (insulators do not)
Ex. Appliance Cords
4. Objects can be charged by the transfer of electrons
Ex. You slide across the fabric car seat some electrons can be transferred form on material to another (charged by friction)

5. II. Electric Force
Force of attraction or repulsion between objects due to charge
1. Electric force depends on charge and distance
2. Electric force acts through a field
Electric field – the region around a charged object in which other charged objects experience

6. Like charges field lines

7. Opposite charges

8. D. Static Electricity and Charging
Charge can be transferred by friction, by contact, and by induction
Law of conservation of charge : The total charge in an isolated system is constant

9. 1. Charging by friction

10. 2. Charge by contact

11. 3. Charge by induction

12. Current I. Voltage and Current
Electrical potential energy – potential energy of a charged object due to its position in an electric field
1. Potential Difference is measured in volts (often called voltage)

13. 2. There is voltage across the terminals of a battery

14. 3. Cell Device that is a source of electric current
They convert chemical energy to electrical energy
They contain electrolytes( conduct electricity)
They contain 2 electrodes with different conducting materials

15. 4. Voltage
Sets charges in motion
Current – rate that electric charges move through a conductor
SI unit for current = Ampere (Amp)

16. II. Electrical Resistance
Light bulbs 40W or 100W shine differently because of the amounts of current

17. 1. Different current is due to their resistance
Resistance- ratio of the voltage across a conductor to the current it carries
R = V/ I or Resistance = voltage/current
SI units
Resistance= ohm (Ω)
Voltage = Volts (V)
Current = Amperes ( amp)

18. Example R=V/I
What resistance would produce a current of 150 ampere with a potential difference of 5000 volts?
R = 5000/50
R = 33.3Ω

19. Example 2 R=V/I
A 12 volt battery produces a current of 30 amperes. What is the resistance?
R = 12/30
R = 0.04Ω

20. Example 3 R=V/I
Find the current when a 12-volt battery is connected through a resistance of 36 ohms.
I = V/R
I = 12/36
I= .333 amps

21. 3. Conductors have low resistance
4. Some materials become superconductors below a certain temperature.
Critical temperature- falls below a -272°C and -123°C
Superconductor : niobium, tin, mercury, oxygen

22. 5. Insulators have high resistance
Grounding is an important part of electrical safety. (provide a pathway for the current to leave the charged object)
6. Semiconductors- in pure state they are insulators

23. I. Circuits
Electric circuit- device connected so that it provides one or more complete paths for movement

24. II. Series Circuits
Series- describes a circuit or portion of circuit that provides a single conducting path

25. III. Parallel Circuit
Describes components in a circuit that are connected across common points providing two or more separate conducting paths

26. Identify the following as series or parallel

27. IV. Electric Power and Electric Energy
1. Power = Current x Voltage
Or P = IV
SI UNITS:
Power = Watts
Current = amperes
Voltage = Volts

28. Example 1. P = IV
A 6- volt battery produces a current of 0.05 amps. What is the power in the circuit?
P = 6 x 0.05
P = 0.3

29. V. Fuses and Circuits Breakers
2. Electric companies measure energy consumed in kilowatts and hours
1kW x hour = 3.6 x 106 J
V. Fuses and Circuits Breakers
Two or more wires touch = short circuit

30. V. Fuses and Circuits Breakers Two or more wires touch = short circuit
1. Fuses – an electrical device containing a metal strip that melts when current becomes too great

31. 2. Circuit Breaker
Device that protects a circuit from current overloads

32. IV. Electric devices
A. Electronics convey information with electrical patterns called analog and digital
1. Analog signals – smooth varying signal produced by continuously changing the voltage or current in a circuit
2. digital signals – encodes information as a string of 1’s and 0’s. Works like Morse code. Digital is more reliable than analog