# Electrical Force Unit 1.3.

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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. 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. m1m2 N m2 Fg= G Where G = 6.67 x 10-11 d2 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 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

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 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 Flow caused by “potential” difference
Fluid system Electrical system 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) Electrical circuit Control Voltage source Electrical Load conductors

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 1.5 v - + 3.0 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.