1. Electrical Force
Unit 1.3

2. Objectives
Explain the similarities and differences between Newton’s law of universal gravitation and Coulomb’s law.
Explain how the force between two like charges and the force between two unlike charges are different.
Describe how to create an electric field.
Define electric potential difference or voltage.
Differentiate between AC and DC .
Identify the most common sources of DC voltage.
Describe how to connect DC voltage sources so that voltages will add.

3. Gravitational Force
Newton’s universal law of gravitation Every object in the universe attracts every other object with a force that is directly proportional to the mass of each body and that is inversely proportional to the square of the distance between them.
m1m2
N m2
Fg= G
Where G = 6.67 x 10-11 d2
kg2

4. Electric Charge
Charge – the property of an object that causes electrical force.
Positive and Negative charges exist.
Like charges repel
Unlike charges attract (opposites attract) + -

5. Gravity and Electrical Force
Both are inverse square laws
Both give magnitude of the force one object exerts on another
Gravitational force is always attractive, but electrical force can be attractive or repulsive.
Gravitational forces govern large bodies
Electrical forces govern smaller bodies

6. Origins of electrical charge
Anatomy of an atom?
Protons – Positive charge
Neutrons – Neutral charge
Electrons – Negative charge
Normal atom has no net charge
Electrons can move in some substances
Principle of conservation of charge
The net electrical charge in an isolated system never changes. (hair and comb)

7. Electrical Force Charles Coulomb and his law q1q2 charges N m2 FE= K
The electrical force between two charged bodies is directly proportional to the charge on each body and inversely proportional to the square of the distance between them.
charges
q1q2
N m2
FE= K
Where K = 9.0 x 109 d2 C2
Distance
SI unit = Coulomb (C)
Elementary Charge - Charge on one electron or proton = 1.6 x C

8. Gravitational and Electrical Fields
The fields are the space between two masses or charges and the effects within them.
Opposite charges
Positive charge
Negative charge
Opposite plates
Like charges

9. Electrical Potential
When charges are within an electric field an electrical potential difference is created.
Volt – unit of measurement for potential difference. (electrical potential, voltage)
Voltage is the prime mover in electrical systems (like pressure in fluid system).

10. Electrical Potential Flow caused by “potential” difference
Fluid system
Electrical system
Current – Flow

11. Sources of Difference A pump is a source of fluid pressure difference
A battery is a source of electrical potential difference

12. Components of Electrical Systems
Voltage source (battery or generator)
Conductors (wires or circuit board)
Load (motor, lights, etc.)
Control element (switch)
Electrical circuit
Control
Voltage source
Electrical Load
conductors

13. AC vs. DC Direct Current (DC) – charge flows in one direction.
Batteries
Solar Panels
Alternating Current (AC) – charge flows back and forth.
Alternators
Generators

14. Batteries Cell – a single unit housing one or more chemical.
Battery – consist of several cells
How does it work?
Chemicals react and electrons are removed creating a potential difference (voltage)
Primary Cells – one time use batteries (cannot be recharged)
Secondary Cells – Can be recharged

16. Connecting cells
Electrodes – the positive and negative terminals on a battery (cell).
Positive electrode (red) called anode.
Negative electrode (black) called cathode.
Voltages add when cells are connected in series. - + - +
Battery
Battery
1.5 v
1.5 v - +
3.0 v

17. A Simple DC Circuit

18. AC Circuits
An AC voltage source reverses the positive and negative terminals many times per second.
The current flows one direction and then the other then the other…..
This changing of polarity or cycling is called frequency, measured in cycles per second (hertz).

19. AC vs DC

20. Where does AC come from?
The main source of 60hz current comes from electrical power plants, through power lines and into your homes.
Generally 110 – 120 volts
Some larger electrical devices need 220 – 240 volts.

21. Summary
Newton’s law of universal gravitation and Coulomb’s law are both inverse squares laws. The magnitudes of both forces decrease with the square of the distance between the masses and the charges.
Atoms are composed of proton, neutrons and electrons. Protons are positively charged, electrons are negatively charged, and neutrons have no charge.
The flow of electrons in an electrical system is a current.
Unlike charges attract, like charges repel.

22. Summary (cont.)
An electric field is a model of the alteration of space around one or more charges. You can use the field to predict the force exerted on a charge placed in a the field.
The potential difference, or voltage, between two points in a uniform electric field is the product of the field strength and the distance between the points.
Voltage is the prime mover in electrical systems.
A battery is a source of DC voltage. It can maintain a current in an electrical circuit.
Batteries or cells can be connected in series to increase voltage.