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Electrical Force. Unit 1.3. 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.

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objectives
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.
gravitational force
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

electric charge
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)

+

-

gravity and electrical force
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
origins of electrical charge
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)
electrical force7
Electrical Force
  • Charles Coulomb and his law
    • 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 10-19 C

gravitational and electrical fields
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

electrical potential
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).
electrical potential10
Electrical Potential

Flow caused by “potential” difference

Fluid system

Electrical system

Current – Flow

sources of difference
Sources of Difference

A pump is a source of fluid pressure difference

A battery is a source of electrical potential difference

components of electrical systems
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

ac vs dc
AC vs. DC
  • Direct Current (DC) – charge flows in one direction.
    • Batteries
    • Solar Panels
  • Alternating Current (AC) – charge flows back and forth.
    • Alternators
    • Generators
batteries
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
connecting cells
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

ac circuits
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).
where does ac come from
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.
summary
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.
summary cont
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.
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