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. 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 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.

Fg= Gm1m2

d2Where G = 6.67 x 10-11

N m2

kg2

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 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 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 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.

FE= Kq1q2

d2Where K = 9.0 x 109

N m2

C2

charges

Distance

SI unit = Coulomb (C)Elementary Charge - Charge on one electron or proton = 1.6 x

10-19 C

Gravitational and Electrical Fields

The fields are the space between two masses or charges and the effects within them.

Positive charge

Negative charge

Opposite plates

Opposite charges

Like charges

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 Potential

Fluid system

Electrical system

Flow caused by “potential” difference

Current – Flow

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

Voltage source (battery or generator)

Conductors (wires or circuit board) Load (motor, lights, etc.) Control element (switch)

Voltage

source

Control

Electrical Load

Electrical circuit

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 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 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

3.0 v

1.5 v

A Simple DC Circuit

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).

AC vs DC

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 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.) 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.