1. ELECTRICITY

2. Electric Charge Electrons negatively charged
property of matter that creates electric and magnetic forces and interactions.
electric charge depends on the imbalance of its protons and electrons.
Electrons negatively charged
protons positively charged
neutrons are neutral (no charge).
Like charges repel
opposite charges attract.

3. E l e c t r i c c h a r g e L i k e c h a r g e s r e p e l .
O p p o s i t e c h a r g e s a t t r a c t .

4. Electric Charge
Negatively charged objects have more electrons than protons.
Positively charged objects have fewer electrons than protons.
SI unit:
coulomb, C.

5. Electric Charge electrical conductor:
material in which charges can move freely and that can carry an electric current.
electrical insulator:
material that does not transfer current easily.
Objects can be charged by the transfer of electrons.
outermost electrons can be easily transferred from one atom to another.
Charging by friction
when one material gains electrons and becomes negatively charged, and the other loses electrons and becomes positively charged.

6. INDUCED CHARGES polarization
Alignment of charges at surface of an object producing an electric charge
Positive & negative charges on opposite sides

7. Charging by Contact
charge a neutral object by touching it with a charged object.
The transfer of electrons to the metal doorknob gives the doorknob a net negative charge.
When a negative rod touches a neutral doorknob, electrons move from the rod to the doorknob.

8. Static Electricity Static Discharge
movement of electrons to relieve a separation in charge

9. Electric Force
force of attraction or repulsion between objects due to charge.
atomic and molecular level is responsible for most of the common forces we can observe.
Electric force depends on charge and distance.
is proportional to the product of charges on objects.
is inversely proportional to square of distance between two objects.

10. Electric Force
region in space around a charged object that causes a stationary charged object to experience an electric force.

11. ELECTRIC FIELD LINES
point in direction of electric force on a positive charge.
around a positive charge point outward.
around a negative charge point inward.
Electric field lines never cross one another.
show both direction of an electric field and relative strength due to a given charge.
More lines are drawn for greater charges to indicate greater force.

12. Electric Field Lines

13. Electric Field Lines

14. CURRENT

15. ELECTRICAL POTENTIAL ENERGY
ability to move an electric charge from one point to another.
EPE of moving charge decreases because electric field does work on charge.
EPE depends on distance between two charged objects for both an attractive and a repulsive electric force.

16. Electrical Potential Energy
The electrical potential energy between two negative charges decreases as the distance between them increases.

17. Electrical Potential Energy and Relative Position
The electrical potential energy of a charge depends on its position in an electric field.

18. POTENTIAL DIFFERENCE
work that must be done against electric forces to move a unit charge from one point to the other.
measured in volts, V
VOLT
equivalent to one joule per coulomb (1 J/C).
aka voltage.

19. Voltage and Current Cell:
device that is a source of electric current because of a potential difference (voltage) b/w terminals.
Positive & negative.
Batteries convert chemical energy into electrical energy.

20. VOLTAGE Measure of energy available to move electrons.
Electrical potential difference b/w two points.
sets charges in motion.

21. CURRENT rate that electric charges move through a conductor. SI unit:
ampere, A.
1 amp = 1 C/s
battery is a direct current source b/c charges always move from one terminal to other in same direction.
Conventional current
= movement of positive charge.
direction of current in a wire is opposite direction that electrons move in that wire.

22. Electrical Resistance
opposition posed by a material or a device to the flow of current.
caused by internal friction
which slows the movement of charges through a conducting material.
SI unit:
ohm, Ω.
1 Ω = 1 V/A
Resistor:
special type of conductor used to control current.

23. R V I OHM’S LAW Resistance = voltage/current
V: potential difference (V)
I: current (A)
R: resistance R V I

24. R V I R = 160  I = V ÷ R V = 120 V I = (120 V) ÷ (160 ) I = ?
A light bulb with a resistance of 160 Ω is plugged into a 120 V outlet. What is the current flowing through the bulb?
GIVEN:
R = 160 
V = 120 V
I = ?
WORK:
I = V ÷ R
I = (120 V) ÷ (160 )
I = 0.75 A I V R

25. Practice with Ohm’s Law
Volts
Amps 4
100 25 15
150 10 2 30 9 45 5 6 48 8

26. Electrical Resistance
Conductors
have low resistances.
Superconductors
Certain metals & compounds have zero resistance when their temperature falls below a certain temperature (critical temperature).
Semiconductors
intermediate to conductors and insulators.

27. CIRCUITS

28. What Are Circuits? Electric circuit:
set of electrical components connected so that they provide one or more complete paths for the movement of charges.
closed path through which electrons can flow
Switches control the flow of charges in a circuit.

29. SCHEMATIC DIAGRAMS
graphical representation of a circuit that uses lines to represent wires and different symbols to represent components.

30. SCHEMATIC DIAGRAMS
A - battery C - light bulb
B - switch D - resistor

31. Series Circuits current travels in a single path
one break stops the flow of current
current is the same throughout circuit
lights are equal brightness
each device receives a fraction of the total voltage
get dimmer as lights are added

32. Series Circuit

33. Parallel Circuits current travels in multiple paths
one break doesn’t stop flow
current varies in different branches
takes path of least resistance
“bigger” light would be dimmer
each device receives the total voltage
no change when lights are added

34. Parallel Circuit

35. Household Circuits Combination of parallel circuits
too many devices can cause wires to overheat
Safety Features:
fuse
electrical device that contains a metal strip that melts when current in circuit becomes too great. metal melts, breaking circuit
circuit breaker
a switch that opens a circuit automatically when the current exceeds a certain value;
bimetallic strip bends when hot, breaking circuit

36. Electric Power and Electrical Energy
energy that is associated with charged particles because of their positions.
SI unit:
watt (W).

37. POWER EQUATION
Electrical Power
rate at which electrical energy is converted to another form of energy
P: power (W)
I: current (A)
V: potential difference (V) P V I

38. V P I I = 0.01 A P = I · V V = 9 V P = (0.01 A) (9 V) P = ? P = 0.09 W
A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use?
GIVEN:
I = 0.01 A
V = 9 V
P = ?
WORK:
P = I · V
P = (0.01 A) (9 V)
P = 0.09 W P I V

39. Electrical Energy
energy use of an appliance depends on power required and time used
E: energy (kWh)
P: power (kW)
t: time (h) E t P

40. t E P P = 700 W = 0.7 kW E = P · t E = (0.7 kW) (10 h) t = 10 h
A refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day?
GIVEN:
P = 700 W = 0.7 kW
t = 10 h
E = ?
WORK:
E = P · t
E = (0.7 kW) (10 h)
E = 7 kWh E P t