Unit 2 Electrical Quantities and Ohm’s Law · Electrical Quantities and Ohm’s Law A complete path must exist before electricity can flow through a circuit. A circuit with a complete
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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.
Unit 2
Electrical Quantities and Ohm’s Law
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.
Unit 2
Electrical Quantities and Ohm’s Law
Compare and contrast these two systems.
Unit 2
Electrical Quantities and Ohm’s Law
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.
Unit 2
Electrical Quantities and Ohm’s Law
Conventional current flow theory and electron flow theory.
Unit 2
Electrical Quantities and Ohm’s Law
Electrons moving from atom to atom.
Unit 2
Electrical Quantities and Ohm’s Law
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).
Unit 2
Electrical Quantities and Ohm’s Law
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.
Unit 2
Electrical Quantities and Ohm’s Law
A simple switch
closes and
opens an
electrical
circuit.
Unit 2
Electrical Quantities and Ohm’s Law
A short circuit has an unintended shorter pathway.
Unit 2
Electrical Quantities and Ohm’s Law
The basic principle of the instantaneous effect of
electric impulses.
Unit 2
Electrical Quantities and Ohm’s Law
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.
Unit 2
Electrical Quantities and Ohm’s Law
A volt or voltage is electrical pressure.
Unit 2
Electrical Quantities and Ohm’s Law
An ohm is the unit of resistance or opposition to the flow of
electricity.
Unit 2
Electrical Quantities and Ohm’s Law
The watt is the unit of electrical power.
Unit 2
Electrical Quantities and Ohm’s Law
Force equals flow rate times pressure.
Unit 2
Electrical Quantities and Ohm’s Law
Amperes times volts equals watts.
Unit 2
Electrical Quantities and Ohm’s Law
Common power units.
Unit 2
Electrical Quantities and Ohm’s Law
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
Electrical Quantities and Ohm’s Law
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
Electrical Quantities and Ohm’s Law
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
Unit 2
Electrical Quantities and Ohm’s Law
Using the Ohm’s law chart.
E = I x R I = E / R R = E / I
Unit 2
Electrical Quantities and Ohm’s Law
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
Electrical Quantities and Ohm’s Law
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
Electrical Quantities and Ohm’s Law
Metric Units
Unit 2
Electrical Quantities and Ohm’s Law
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