Electrical PrinciplesElectrical PrinciplesChapter 3Chapter 3

Resistance, Power, Coulombs, Ohm’s Resistance, Power, Coulombs, Ohm’s Law, Power Formula, Power – Current Law, Power Formula, Power – Current

Relationships, Impedance, Multimeters, Relationships, Impedance, Multimeters, Calculating-Measuring Energy and PowerCalculating-Measuring Energy and Power

Resistance and Ohm’sResistance and Ohm’s

Resistance and Ohm’sResistance and Ohm’s

ResistanceResistance is the opposition to current is the opposition to current flow by the dissipation of heat.flow by the dissipation of heat.The Resistor is a device that is included The Resistor is a device that is included within electrical and electronic circuits to within electrical and electronic circuits to oppose current flow by introducing a oppose current flow by introducing a certain value of circuit certain value of circuit Resistance.Resistance.Resistance is measured in Ohms and is Resistance is measured in Ohms and is represented by the Geek letter Omega, represented by the Geek letter Omega, the symbol for Omega is the symbol for Omega is ΏΏ..

Resistance and Ohm’sResistance and Ohm’s

The larger the resistance, the larger the The larger the resistance, the larger the value of Ohms and the more the resistor value of Ohms and the more the resistor will oppose current flow.will oppose current flow.

As the resistance in the circuit is increased As the resistance in the circuit is increased the current will decrease and, conversely, the current will decrease and, conversely, as the resistance of the resistor is as the resistance of the resistor is decreased the circuit current will increase.decreased the circuit current will increase.

Ohm’s LawOhm’s Law

In 1827 George Ohm proved there was a In 1827 George Ohm proved there was a direct relationship between Voltage (E), direct relationship between Voltage (E), Current (I), and Resistance (R) in an Current (I), and Resistance (R) in an electrical circuit. This relationship is electrical circuit. This relationship is known as Ohm’s Law.known as Ohm’s Law.

Ohm’s Law states that current in a circuit Ohm’s Law states that current in a circuit is proportional to the voltage and inversely is proportional to the voltage and inversely proportional to the resistance.proportional to the resistance.

Ohm’s LawOhm’s Law

R

E

IE = Voltage - VoltsI = Current - AmpsR = Resistance or Reactance (Impedence) - Ohms

Direction: Cover what you want and perform the mathematical process with what’s left over.Example: Cover E = I X R

Ohm’s LawOhm’s Law

Voltage/Current Relationship. Ohm’s Law Voltage/Current Relationship. Ohm’s Law states that if the resistance in a circuit states that if the resistance in a circuit remains constant, a change in current is remains constant, a change in current is directly proportional to a change in directly proportional to a change in voltage. Example: A heat shrink sealing voltage. Example: A heat shrink sealing gun connected to a variable power supply.gun connected to a variable power supply.

Ohm’s LawOhm’s Law

Current/Resistance Relationship. Ohm’s Current/Resistance Relationship. Ohm’s Law states that if the voltage in a circuit Law states that if the voltage in a circuit remains constant, a change in resistance remains constant, a change in resistance produces an inversely proportional change produces an inversely proportional change in current. The current in a circuit in current. The current in a circuit decreases with an increase in resistance, decreases with an increase in resistance, and the current in the circuit increases with and the current in the circuit increases with a decrease in resistance. Example: The a decrease in resistance. Example: The dimmer/brightness switch for lights inside dimmer/brightness switch for lights inside a car.a car.

Ohm’s LawOhm’s Law

In engineering applications, Ohm’s Law is In engineering applications, Ohm’s Law is used to solve for the proper values of used to solve for the proper values of voltage, current, or resistance during voltage, current, or resistance during circuit design and to predict circuit circuit design and to predict circuit characteristics before power is applied to a characteristics before power is applied to a circuit when two of the three electrical circuit when two of the three electrical values are know.values are know.

Ohm’s LawOhm’s Law

In troubleshooting applications, Ohm’s In troubleshooting applications, Ohm’s Law is used to determine how a circuit Law is used to determine how a circuit should operate and how it is operating should operate and how it is operating under power.under power.Resistance measurements can not be Resistance measurements can not be taken when a circuit is under load (power).taken when a circuit is under load (power).Current and Voltage can be taken when a Current and Voltage can be taken when a circuit is under load (power).circuit is under load (power).

PowerPower

PowerPower

Transforming energy from one form to Transforming energy from one form to another is called another is called workwork. The greater the . The greater the energy transformed, the more work that is energy transformed, the more work that is done.done.There are six basic forms of energy and There are six basic forms of energy and they are light, heat, magnetic, chemical, they are light, heat, magnetic, chemical, electrical, and mechanical energy.electrical, and mechanical energy.The unit for measuring The unit for measuring workwork is called the is called the Joule (J).Joule (J).

PowerPower

Power (P)Power (P) is the rate at which is the rate at which workwork is is performed and is measured by the unit performed and is measured by the unit called called Watt (W). Watts = Joules per Watt (W). Watts = Joules per second.second.The output The output Power, or power ratingsPower, or power ratings of of electrical, electronic or mechanical devices electrical, electronic or mechanical devices can be expressed in can be expressed in Watts (W)Watts (W) and and describes the number of describes the number of JoulesJoules of energy of energy converted every second.converted every second.

PowerPower

The output of The output of PowerPower of rotating machines of rotating machines is given in the unit is given in the unit horsepower (hp)horsepower (hp)..

The output of The output of PowerPower of heaters is given in of heaters is given in the unit the unit British Thermal Units per hour British Thermal Units per hour (BTU/h)(BTU/h)

The output of The output of PowerPower of cooling units is of cooling units is given in the unit given in the unit Ton of RefrigerationTon of Refrigeration..

PowerPower

Despite the different names, all can be Despite the different names, all can be expressed in the unit of expressed in the unit of Watts (W)Watts (W) by by using the following conversions:using the following conversions:

1 hp = 746 W1 hp = 746 W1 BTU/h = 0.293 W1 BTU/h = 0.293 W1 1 ton of refrigerationton of refrigeration = 3520 W = 3520 W

The amount of energy stored (The amount of energy stored (WW) is ) is dependent on the coulombs of charge dependent on the coulombs of charge stored (stored (QQ) and the voltage () and the voltage (VV) and can be ) and can be expressed mathematically expressed mathematically W = Q x V.W = Q x V.

PowerPower

PowerPower is the rate at which electric energy is the rate at which electric energy ((WW) is converted to some other form and ) is converted to some other form and can be expressed mathematically as can be expressed mathematically as P = I x V.P = I x V.

This formula states that the amount of This formula states that the amount of power delivered to a device is dependent power delivered to a device is dependent on the electrical pressure (or voltage on the electrical pressure (or voltage applied across the device) and the current applied across the device) and the current flowing through the device.flowing through the device.

Power FormulaPower Formula

The The Power FormulaPower Formula is the relationship is the relationship between Power (P), Voltage (E), and between Power (P), Voltage (E), and Current (I).Current (I).

P

E IP = Power -WattsE = Voltage - VoltsI = Current - Amps

Direction: Cover what you want and perform the mathematical process with what’s left over. Example: Cover E = I X R

Power FormulaPower Formula

The The Power FormulaPower Formula states that if the states that if the voltage in a circuit changes, the current in voltage in a circuit changes, the current in the circuit also changes. The power the circuit also changes. The power required from a circuit changes any time required from a circuit changes any time loads are added (power increases) or loads are added (power increases) or removed (power decreases).removed (power decreases).The The Power FormulaPower Formula is used when is used when troubleshooting and to predict circuit troubleshooting and to predict circuit characteristics before power is applied.characteristics before power is applied.

Combining Ohm’s Law and Combining Ohm’s Law and Power FormulaPower Formula

Ohm’s LawOhm’s Law and the and the Power FormulaPower Formula may be may be combined mathematically and written as any combined mathematically and written as any combination of Voltage (E), Current (I), combination of Voltage (E), Current (I), Resistance (R), or Power (P).Resistance (R), or Power (P).

Ohm’s LawOhm’s Law and the and the Power FormulaPower Formula are limited are limited to circuits in which electrical resistance is the to circuits in which electrical resistance is the only significant opposition to the flow of current. only significant opposition to the flow of current. This limitation includes all DC circuits and AC This limitation includes all DC circuits and AC circuits that do no contain a significant amount of circuits that do no contain a significant amount of inductance and/or capacitance – which we will inductance and/or capacitance – which we will learn about later.learn about later.

Combining Ohm’s Law and Combining Ohm’s Law and Power FormulaPower Formula

ReviewReview

Ohm’s Law states that current in a circuit Ohm’s Law states that current in a circuit is proportional to the voltage and inversely is proportional to the voltage and inversely proportional to the resistance.proportional to the resistance.The The Power FormulaPower Formula states that if the states that if the voltage in a circuit changes, the current in voltage in a circuit changes, the current in the circuit also changes. The power the circuit also changes. The power required from a circuit changes any time required from a circuit changes any time loads are added (power increases) or loads are added (power increases) or removed (power decreases).removed (power decreases).

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