Unit 2 Electrical Quantities and Ohm’s Law · Electrical Quantities and Ohm’s Law A complete...

Unit 2

Electrical Quantities and Ohm’s Law

A coulomb is a quantity measurement for

electrons.

One coulomb contains 6.25 x 1018

electrons, or 6,250,000,000,000,000,000

electrons.

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The ampere is a measurement of the amount of

electricity that is flowing through a circuit.

One ampere (A) is defined as one coulomb of

electricity flowing past a given point in one

second.

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Compare and contrast these two systems.

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There are two theories about current flow.

Electron flow theory describes current flow from

negative to positive.

Conventional current flow theory states

electrical current flows from positive to

negative.

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Conventional current flow theory and electron flow theory.

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Electrons moving from atom to atom.

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Electrical sources are divided into two basic

types:

– Direct Current (DC) which is unidirectional

(one way).

– Alternating Current (AC) which is

bidirectional (two way, or back and forth).

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A complete path must exist before electricity can

flow through a circuit.

A circuit with a complete path for electrical flow is

called a closed circuit.

If the circuit path is incomplete or broken, this is

called an open circuit.

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A simple switch

closes and

opens an

electrical

circuit.

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A short circuit has an unintended shorter pathway.

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The basic principle of the instantaneous effect of

electric impulses.

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The impulse of electricity can travel faster than light. It would take light 1.3 seconds to travel around the earth 10 times. If a wire were wrapped around the earth 10 times, when the switch was closed the light would come on almost instantly.

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A volt or voltage is electrical pressure.

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An ohm is the unit of resistance or opposition to the flow of

electricity.

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The watt is the unit of electrical power.

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Force equals flow rate times pressure.

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Amperes times volts equals watts.

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Common power units.

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Ohm’s law states that in a DC (Direct

Current) circuit, the current is directly

proportional to the voltage and inversely

proportional to the resistance.

E (volts) = I (amps) x R (ohms)

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Ohm’s Law Symbols:

P is the symbol for Watts.

E is the symbol for Volts.

I is the symbol for Amperes.

R is the symbol for Resistance or Ohms.

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Ohm’s Law states that it takes one volt to push

one ampere through one ohm.

E = Volts

I = Amps

E = I x R

I = E / R

R = E / I

R = Resistance

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Using the Ohm’s law chart.

E = I x R I = E / R R = E / I

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Adding P (watts) to the Ohm’s law chart.

P = E2 / R

P = E x I

P = I2 x R

R = E / I

R = P / I2

R = E2 / P

I =

I = P / E

I = E / R

E =

E = I x R

E = P / I

RP

PR

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Remember:

E = EMF, or voltage

I = intensity of current, or amperage

R = resistance in ohms

P = power in watts

E (volts) = I (amperes) x R (ohms)

P (watts) = I (amperes) x E (volts)

Unit 2


Metric Units

Unit 2


Unit 2 Electrical Quantities and Ohm’s Law · Electrical Quantities and Ohm’s Law A complete...

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