Unit 2 Electrical Quantities

Unit 2

Electrical Quantities

and Ohm’s Law

Unit 2

Electrical Quantities and Ohm’s Law

Objectives:

• Define a coulomb.

• Define an ampere.

• Define a volt.

• Define an ohm.

• Define a watt.

Unit 2


Objectives:

• Compute electrical values using Ohm’s

law.

• Discuss basic types of circuits.

• Use the Ohm’s wheel charts.

Unit 2


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)

Unit 2


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.

Unit 2


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

Unit 2


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


Review:

1. A coulomb is a quantity measurement of

electrons.

2. An ampere (A) is one coulomb per second.

3. Either the letter I, which stands for intensity

of current flow, or the letter A, which stands

for amperes, can be used in Ohm’s law

formulas.

Unit 2


Review:

4. Voltage is referred to as electric pressure,

potential difference, or electromotive force.

An E or a V can be used to represent

voltage in Ohm’s law formulas.

5. An ohm (Ω) is a measurement of resistance

(R) in an electric circuit.

Unit 2


Review:

6. The watt (W) is a measurement of power in

an electrical circuit. It is represented by

either a W or a P (power) in Ohm’s law

formulas.

7. Electric measurements are generally

expressed in engineering notation.

Unit 2


Review:

8. Engineering notation differs from the

standard metric system in that it uses steps

of 1000 instead of steps of 10.

9. Before current can flow, there must be a

complete circuit.

10. A short circuit has little or no resistance.

Unit 2 Electrical Quantities

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