1. Unit 2
ELECTRICITY

2. Electrostatics is the study Of electrical charges that
Can be collected and held in
One place.

3. If the positive charges and the Negative charges balance, an
Item is said to be neutral.
An insulator is something in
Which charge does not move easily.
A conductor is something in
Which charges move easily through.

4. Electrical forces must be strong, Because they easily produce
Accelerations larger than the
One caused by gravity.

5. There are 4 major rules to Remember about electrical forces:
There are two kinds of electrical
Charges, positive & negative.
Charges exert a force on other
Charges over a distance.

6. The force is stronger when the Charges are closer together.
And
Like charges repel, opposite
Charges attract.

7. When you charge something by Conduction, you are touching the
Object to transfer electrons.
When you charge something by
Induction, you are just getting
A charge close to something
To transfer charge.

8. Electricity did not become an integral Part of our daily lives until
Scientists learned to control the
Movement of electric charge.
This is known as current

9. Electric currents are responsible For many things; computers,
Cars, and every move you make.
Current is the rate at which
Electric charges move through
A given area.

10. Batteries and generators Supply energy to charge carriers.
Both batteries and generators
Contain a potential difference
(volts) across their terminals.
Batteries use chemical energy
And generators use mechanical
Energy.

11. Current can be direct or alternating.
In Direct Current (DC) the charge
Moves only one way through the
Wire. (like my electric truck)
In Alternating Current (AC), the
Charges are constantly changing,
Creating no real movement of
Electrons.
Our house current in the US is
60 Hz.

12. The SI unit for current is the Ampere (A).
The SI unit for charge is the
Coulomb (C).
So the Ampere is 1 C per second.

13. Click image to view the movie - stupid.

14. There are insulators and Conductors, but there are also
Not so good conductors.
The impedance of the motion of
Charge through a conductor
Is the conductor’s resistance.
Resistance is the ratio of the
Potential difference across
A conductor to the current
It carries.

15. Ohm’s law states that the Resistance is constant over a
Wide range of applied
Potential differences.
It is usually shown by…
V = IR
SI unit for resistance is the Ohm,
And is represented by Ω.

16. Resistance depends on length, Cross-sectional area, material,
And temperature.
Resistors can be used to control
The amount of current
In a conductor.

17. The plate on an iron states that The current in the iron is 6.4 A
PROBLEM...
The plate on an iron states that
The current in the iron is 6.4 A
When the iron is connected across
A potential difference of 120V.
What is the resistance of the iron?
R = 19 Ω

18. Electric power is the rate of Conversion of electrical energy.
P = IV
The SI unit is the Watt.

19. An electric space heater is Connected to a 120 V outlet. The
PROBLEM...
An electric space heater is
Connected to a 120 V outlet. The
Heater dissipates 3.5 kW of power
In the form of heat. Calculate
The resistance of the heater.
R = 4.1 Ω

20. An electric circuit is a Continuous path through which
Electric charges can flow.
There are two types of circuit
Connections…
Parallel & Series

21. A parallel circuit is one with Several current paths, whose
Total current equals the sum of the
Currents in its branches.

22. A series circuit is one in which Current passes through one
Device and then another.

24. Electric companies measure
Energy consumption in
Kilowatt-hours.
1 kW h = 3.6 X 106 J

25. Current moving through a resistor Causes it to heat up because
Flowing electrons bump into the
Atoms in the resistor.
These collisions increase the
Atoms’ kinetic energy and, thus,
The temperature of the resistor.

26. P = I2R V2 R P = V2 R E = t If we rearrange Ohm’s Law, and
The formula for power, we have
3 new formulas that we can use…
And for the thermal
Energy dissipated…
P = I2R V2 R
P = V2 R
E = t

27. Power Electrical Energy is usually converted to
Electromagnetic Energy (light),
Thermal Energy (heat),
or Kinetic Energy (motion).

28. A heater has a resistance of 10 Ω. It operates on 120 V.
PROBLEM...
A heater has a resistance of
10 Ω. It operates on 120 V.
What is the power dissipated by
The heater? What is the thermal
Energy supplied by the heater
In 10 s?
1.44 kW kJ

29. Circuit = the path that flowing electrons follow
If path is continuous, it’s a closed circuit
and electricity can flow.
If path is interrupted, it’s an open circuit
and electricity can NOT flow.

30. Series Circuits Current goes through one pathway only.
Same amount of current goes through each component (battery, resistor, etc.).
The total resistance of resistors in series = the sum of each resistance
(add them up).

31. In a series circuit, all of the Resistors are added together
In order to get the
Equivalent Resistance.
R = R1 + R2 + R3 + …
See that the equivalent resistance
Is greater than any individual
Resistor, therefore if the voltage
Does not change, adding more
Resistors always decreases current

32. Three 20 Ω resistors are connected In series across a 120 V generator.
PROBLEM...
Three 20 Ω resistors are connected
In series across a 120 V generator.
What is the equivalent resistance
Of the circuit? What is the current
In the circuit?
R = 60 Ω
I = 2.0 A

33. Parallel Circuits Current divides into 2 or more paths
Voltage drop across components is equal.
The sum of the current in each parallel path = the total current in (or out) of the circuit.

34. In a parallel circuit the resistance Is always smaller than any
One resistor because there are
More branches for the current
To flow through.
Equivalent Resistance for Parallel
1/R = 1/R1 + 1/R2 + 1/R3 + …

35. Three 15 Ω resistors are connected In parallel and placed across
PROBLEM...
Three 15 Ω resistors are connected
In parallel and placed across
A 30 V battery. What is the
Equivalent resistance? What is the
Current through the entire circuit?
What is the current through each
Branch of the circuit?
R = 5 Ω
I = 6 A
I = 2 A

36. Draw a circuit diagram of a series circuit and a
PROBLEM...
Draw a circuit diagram of a
series circuit and a
Parallel circuit that each contain
The following…
Battery, motor, 3 lights, and 2
Resistors.

37. There are many safety devices When dealing with electrical Circuits.
A short circuit is when the
Resistance is very small which
Makes the current very large.

38. When a short happens enough Thermal energy is produced to
Start a fire, or just melt the
Wires if you’re lucky.
A fuse is used to help stop a short
Before it gets too bad.
When a fuse is connected to the
circuit it will melt and “blow”
Before the wires do.

39. A circuit breaker is another kind Of fuse.
It breaks the circuit when the
Current gets too high and a
Switch flips. In order to fix
The circuit, all you have to do is
Flip the switch back.

40. An ammeter is a device used to Measure the current in a circuit.
It is added in series and
Has a low resistance.
A voltmeter measures the
Voltage of a circuit.
It is added in parallel and has
A high resistance (10 kΩ).
A multimeter measures both
And more.

42. Click image to view movie.
Electric Motor
Click image to view movie.

43. The wire coil in an electric motor is called the armature
The wire coil in an electric motor is called the armature. The armature is made of many loops mounted on a shaft or axle.
The magnetic field is produced either by permanent magnets or by an electromagnet, called a field coil.
The torque on the armature, and, as a result, the speed of the motor, is controlled by varying the current through the motor.

44. Electromagnetic Induction
After nearly ten years of unsuccessful experiments, Faraday found that he could induce electric current by moving a wire through a magnetic field.
Electromagnetic Induction
Click image to view the movie - stupid.

45. The difference in potential is called the induced EMF.
When you move a wire through a magnetic field, you exert a force on the charges and they move in the direction of the force.
Work is done on the charges. Their electrical potential energy, and thus their potential, is increased.
The difference in potential is called the induced EMF.

46. Electric Generators
The electric generator, invented by Michael Faraday, converts mechanical energy to electrical energy.
An electric generator consists of a number of wire loops placed in a strong magnetic field.
The wire is wound around an iron core to increase the strength of the magnetic field.
The iron and the wires are called the armature, which is similar to that of an electric motor.

47. The armature is mounted so that it can rotate freely in the magnetic field.
As the armature turns, the wire loops cut through the magnetic field lines and induce an EMF.
Commonly called the voltage, the EMF developed by the generator depends on the length of the wire rotating in the field.
Increasing the number of loops in the armature increases the wire length, thereby increasing the induced EMF.

48. Generators and motors are almost identical in construction, but they convert energy in opposite directions.
A generator converts mechanical energy to electrical energy, while a motor converts electrical energy to mechanical energy

49. Electrons can move more freely in semiconductors than in insulators, but not as easily as in conductors.
Atoms of the most common semiconductors, silicon (Si), and germanium (Ge), each have four valence electrons.

50. The conductivity of intrinsic semiconductors must be increased greatly to make practical devices.
Dopants increase conductivity by making extra electrons or holes available

51. If an electron donor with five valence electrons, such as arsenic (As), is used as a dopant for silicon, the product is called an n-type semiconductor.
If an electron acceptor with three valence electrons, such as gallium (Ga), is used as a dopant for silicon, the product is called a p-type semiconductor

52. Click image to view movie.
Diodes
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53. These diodes are called light-emitting diodes, or LEDs
When electrons reach the holes in the junction, they recombine and release the excess energy at the wavelengths of light
These diodes are called light-emitting diodes, or LEDs

54. Transistors and Integrated Circuits
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55. Questions?

56. THE END