Chapter 17: Introduction to Electricity
Review

1. Definitions: a) law of electric charges
(like charges repel and opposite charges attract) b) electric force
(the force between charged objects), c) electric field
(space surrounding electrically charged particles), d) electrical conductor
(a substance in which charges can roam), e) electrical insulator
(a substance in which charges do not roam), f) static electricity
(an electric charge at rest on an object), g) electric discharge
(the loss of static electricity as charges run off of an object), h) electric current
(the rate at which charges pass through a specified point),

Definitions i) voltage
(potential difference between two points in a circuit), j) resistance
(the opposition to the flow of electric charge), k) electric power
(the rate at which electrical energy is converted into other forms of energy), l) series circuits
(all parts are connected in a single loop), m) parallel circuits
(loads are connected-side-by side).

2. The three ways of charging an object
1. Conduction : electrons move between objects by direct contact
2. Induction : rearrangement of charges in an uncharged object without direct contact
3. Friction transfer of charge through rubbing/wiping

3. Electrical insulator and conductors
• Examples of insulators: plastic, rubber, glass, wood, etc.
• Examples of conductors: copper, aluminum, mercury, etc.

• AC current: charges continually change direction
Applications: houses ( AC changes direction 120 times a second )
• DC current: charges flow in the same direction.
Applications: batteries

5. The relationship between voltage, resistance and current
• If voltage increases, current also increases
• Resistance increases as current goes down
(voltage must be constant)

6. Resistance, thickness, length, and temperature
• Resistance decreases with thickness
• Resistance increases with length
• Resistance increases with an increase in temperature
(virtually at low temperature there is no resistance) e.g. superconductors

Ohm’s law:
V = I * R electrical power: P = V * I electrical energy ( E = P * t )

17.3: Ohm’s Law
Current vs. Voltage
Current(A)
1.5
1
0.5
2.5
2
0
0 5 10 15 35 40 45 20 25
Voltage (V)
30
•
Current is proportional to voltage
50

10. Components of an electrical circuit
1. energy source
2. wire
3. load