1. Electricity
Chapter 16

2. Electrical Charge and Force
Section 16.1

3. Introduction Turning the tv on Removing your hand from a hot pan
Speaking into the cell phone
All of these are carried by electrical pulses

4. Electric Charge
A property of matter that creates electric and magnetic forces and interaction
Example: Being shocked opening a metal door
Notice the electric charge as a shock

5. Electric Charge Like charges repel Opposite charges attract Positive
Negative
Example: Rub 2 balloons on your hair, put them close together they repel
So: Hair is positive, the balloons are negative, and both balloons have a negative charge so they repel

6. Electric Charge
Charge of an object depends on imbalance of protons and electrons
REVIEW!! (Write if you don’t remember!)
Everything is made of atoms
Atoms are made of protons, neutrons, and electrons
Protons (+), neutrons (neutral), electrons (-)
An imbalance causes a net charge

7. Electric Charge REVIEW (cont’d)
More electrons = a negative charged object
More protons = a positive charged object
SI Unit for electric charge is the Coulomb (C)
Net charge is always in multiples of 1.6×10-19

8. Electric Charge Conductors and Insulators
Cords to electrical items are wrapped in rubber or plastic but have metal wires in the center
Metal is an electrical conductor (material that charges move freely and carry a current)
Plastic is an electrical insulator (material that does not transfer current easily)
Protects people from shock, efficient

9. Electric Charge Objects can be charged by transferring electrons
Protons and neutrons are found in nucleus
Valence electrons can be transferred
Charging by friction
Slide into car and electrons from seat go to clothing; seat (+) and clothing is (-)
Charging by contact
Touching a door knob

10. Electric Charge Charges move w/in uncharged objects
Neutral object may have an end that is housing all the (+) particles and the other end has all the (-) particles, but still neutral

11. Electric Force
Force of attraction or repulsion between objects due to charge
Holds atoms together
Bonding of atoms
Holds proteins together

12. Electric Force Depend on charge and distance
The force between 2 objects is proportional to the product of the charges
Increase charge = increase the force
Electric force is inversely proportional to the square of the distance of 2 objects
Increase distance = decrease in force to ¼ of original value

13. Electric Force Acts through a field
Electric field- a region in space around a charged object that causes a stationary charged object to experience an electric force

14. Electric Force Field Lines (in reference to a + field)
Point out on (+)
Point in on (-)
Field lines never cross + -

15. Electric Force
Pg 536 Fig 7
Field lines show direction of electric field
Relative strength b/c of charge

16. Current
Section 16.2

17. Voltage and Current REVIEW
GPE depends on the objects position (move from high GPE to low GPE)
Electric potential energy- the ability to move an electric charge from one point to another
Depends on position in electric field

18. Voltage and Current
A (-) charge will move away from another (-) charge

19. Voltage and Current Potential difference is measured in volts (V)
1 J/C
Potential difference- between any 2 points the work that is done against electric forces to move a unit charge from one point to the other; called voltage

20. Voltage and Current
Cell- device that is a source of electric current b/c of a potential difference, or voltage, between the terminals
Example: battery- convert chemical energy to electric energy
Avg cell has a potential difference of 1.5 V
Electrolyte- solution that conducts electricity
Electrodes- conducting materials

21. Voltage and Current Voltage sets a charge into motion
Current- the rate that electric charges move through a conductor
SI Unit- amphere (A)
Direct current- charges move form 1 terminal to the next in the same direction

22. Voltage and Current
Conventional Current is the movement of a positive charge
Direction of the current is opposite to the direction that the electrons move

23. Electrical Resistance
Resistance- the opposition posed by a material or a device to the flow of current
Changes in current cause different watts of light bulbs to shine different
Caused by internal friction
Slows the movement of charges through a conducting material

24. Resistance Resistance can be calculated resistance= voltage/current
R=V/I
SI unit for resistance is ohm (Ω)
Resistor- special type of conductor used to control current

25. Resistances Conductors have low resistances
Basically, metal is not going to slow down the flow of an electric field

26. Resistance
Superconductors- materials that become conductors BELOW a certain temperature (called the critical temperature)
They have zero resistance
Used in:
Filaments
High speed express trains
Super magnets

27. Resistance
Semiconductors- intermediate between conductors and insulators
In pure state- insulators
Impurities added to semiconductors cause them to be conductors

28. Resistance Insulators have high resistance
Prevent the free flow of electric charge
Grounding- conducting wire ran between the charged object and the ground (safety reason)
If a charge is built up, it will be discharged to the Earth safely

29. Circuits
Chapter 16.3

30. Circuit Introduction
Electric circuit is a path through which charges can be conducted
Closed circuit- conducting path produced when a light bulb in connected across the terminals
Open circuit- no complete path, no charge flow, so no current
Voltage source is always part of conducting path

31. Resistors
Lightbulbs
Hair dryers
Stoves TV
Curling Iron

32. Open circuit
Closed circuit

33. Circuits Switches interrupt the flow of charges in a circuit
Switch is used to open or close a circuit
Ex: turn light on and off
Knife switch (see previous pic)
Up=open circuit (no flow)
Down=closed circuit (travel through bar)

34. Circuits Schematic diagrams are used to represent circuits
A graphical representation of a circuit that uses lines to represent wires and different symbols to represent components
Pg 548 Know table 2 symbols

36. Series and Parallel Circuits
Series circuits have a single path for current
Devices hooked into a series will have the same current to pass in all of them
However resistance maybe different
Therefore voltage in each device in a series circuit can be different

38. Series and Parallel Circuits
Parallel circuits have multiple paths
Circuit in which all of the components are connected to each other side by side
Current in each device doesn’t have to be the same
Sum of all the device currents=total current
Different resistances and different voltages

39. Parallel Circuit

40. Electric Power and Electrical Energy
Electrical energy- the energy that is associated w/charged particles b/c of their positions
Electric power is the rate at which electrical energy is used (for work) in a circuit
Electric power=current × voltage
P=IV
SI unit of power is Watts (W)

41. Electric Power and Energy
The power that is lost or “dissipated” by a resistor can be found
P=I2R=V2/R
Power bills are determined by measuring kilowatt-hours

42. Fuses and Circuit Breakers
When too much current is moving through a circuit, the resistance is lowered, and this is now unsafe
This is known as overloading which can cause a fire
Short circuit- when a an alternative pathway for current is created b/c a wire’s insulation breaks down

43. Fuses and Circuit Breakers
Fuses melt to prevent circuit overload
Fuses- metal ribbon w/low melting point, that melts when current becomes to great
“Blown fuse”- 20A fuse blows when the current exceeds 20A
Warning

44. Fuses and Circuit Breakers
Circuit breakers open circuits with high current
When a circuit overloads the circuit breaker opens the circuit
Can reset breakers, unlike fuses