Ch. 5.3Ch. 5.3

Energy in Electrical Energy in Electrical SystemsSystems

Moving Charges and Magnetic Moving Charges and Magnetic FieldsFields

• MovingMoving chargescharges, like those in an , like those in an electric current, produce electric current, produce magneticmagnetic fieldsfields..

• The magnetic field around a wire forms The magnetic field around a wire forms a circular pattern around the wire.a circular pattern around the wire.

• The The directiondirection of the magnetic of the magnetic fieldfield depends on the direction the depends on the direction the currentcurrent flows.flows.

• The The strengthstrength of the field depends on of the field depends on the amount ofthe amount of current current flowing. flowing.

Electromagnets - 1Electromagnets - 1• An An electromagnetelectromagnet is a temporary is a temporary

magnet made by placing a piece of magnet made by placing a piece of iron inside a current-carrying wire.iron inside a current-carrying wire.

• The strength can be increased by The strength can be increased by adding adding moremore turnsturns of wire or of wire or increasingincreasing the amount of current. the amount of current.

• The north and south The north and south polespoles of the of the electromagnet can be reversed by electromagnet can be reversed by reversingreversing the direction of the the direction of the currentcurrent..

Electromagnets - 2Electromagnets - 2

• Magnetic properties can be Magnetic properties can be controlled by controlled by varyingvarying the amount the amount of of currentcurrent..

• A A galvanometergalvanometer is a device that is a device that uses an electromagnet to measure uses an electromagnet to measure electric current.electric current.

Electric MotorsElectric Motors• An An electricelectric motormotor is a device that is a device that

changes electrical energy into changes electrical energy into mechanical energy.mechanical energy.

• An electric motor contains an An electric motor contains an electromagnetelectromagnet that is free to rotate that is free to rotate between two poles of a fixed between two poles of a fixed permanent magnetpermanent magnet..

A - Power SourceB – ElectromagnetC – Permanent Magnet

Electromagnetic InductionElectromagnetic Induction

• ElectromagneticElectromagnetic inductioninduction is the is the production of an electric production of an electric currentcurrent by moving a by moving a looploop of wire through a of wire through a magnetic field or moving a magnetic field or moving a magnetmagnet through a loop of wire.through a loop of wire.

Electric GeneratorsElectric Generators

• An An electricelectric generatorgenerator does just the does just the oppositeopposite of an electric motor. It of an electric motor. It changes mechanical energy into changes mechanical energy into electrical energy.electrical energy.

• This is accomplished by using This is accomplished by using electromagnetic electromagnetic inductioninduction – turning – turning a a coilcoil of wire in a strong of wire in a strong magneticmagnetic field.field.

Generating ElectricityGenerating Electricity• Electricity in the home comes Electricity in the home comes

from from powerpower plantsplants with huge with huge generators.generators.

• Coils of electromagnets in the Coils of electromagnets in the generators are connected to a generators are connected to a turbineturbine, which is a large wheel , which is a large wheel that rotates when pushed by that rotates when pushed by wind, water, or steam.wind, water, or steam.

Chapter 5.4Chapter 5.4

Energy in Thermal Energy in Thermal SystemSystem

Heat EnginesHeat Engines

•HeatHeat enginesengines are device that are device that convert heat energy into convert heat energy into mechanical energy. These mechanical energy. These include:include:– InternalInternal combustioncombustion enginesengines are are

engines that burn fuel inside the engine engines that burn fuel inside the engine in chambers or cylinders. An example in chambers or cylinders. An example is a car engine.is a car engine.

– ExternalExternal combustioncombustion engines burn the engines burn the fuel outside the engine and then fuel outside the engine and then transfer the heat to the engine. An transfer the heat to the engine. An example is a steam locomotive.example is a steam locomotive.

Four-Stroke EnginesFour-Stroke Engines• AutomobilesAutomobiles are four-stroke internal are four-stroke internal

combustion engines. The combustion engines. The fourfour strokes that strokes that power the automobile are listed below.power the automobile are listed below.– IntakeIntake StrokeStroke – Piston raises, takes in fuel – Piston raises, takes in fuel– CompressionCompression StrokeStroke – piston compresses – piston compresses

fuelfuel

in the cylinderin the cylinder– PowerPower StrokeStroke – – Spark plug ignites fuel,Spark plug ignites fuel,

forcing the piston upwardforcing the piston upward– ExhaustExhaust StrokeStroke – Piston moves downward,– Piston moves downward,

forcing exhaust out of the engineforcing exhaust out of the engine

Heat MoversHeat Movers

•HeatHeat moversmovers are devices that are devices that remove thermal energy from one remove thermal energy from one location and transfer it to location and transfer it to another location at a different another location at a different temperature. temperature.

• Examples of heat movers include Examples of heat movers include refrigeratorsrefrigerators and and heatheat pumpspumps..

Measuring TemperatureMeasuring Temperature

• We generally use two temperature We generally use two temperature scales, scales, CelsiusCelsius, which is commonly , which is commonly used for most used for most laboratorylaboratory work and work and the absolute temperature scale, the absolute temperature scale, which is also called the Kelvin scale. which is also called the Kelvin scale.

• The Celsius scale is based on the The Celsius scale is based on the freezing point and boiling point of freezing point and boiling point of waterwater. The 0° point is the freezing . The 0° point is the freezing point and the 100° point is the point and the 100° point is the boiling point.boiling point.

Measuring Temperature - 1Measuring Temperature - 1

• The zero point on the The zero point on the KelvinKelvin scale is scale is the point at which the the point at which the thermalthermal energyenergy of the substance is of the substance is zerozero. It . It is impossible to lower the is impossible to lower the temperature below this point and, temperature below this point and, therefore, the temperature is therefore, the temperature is referred to as referred to as absoluteabsolute zerozero..

• Each Each incrementincrement on this scale is on this scale is called a called a KelvinKelvin. The . The degreedegree symbol symbol is is notnot usedused with the Kelvin scale. with the Kelvin scale.

Celsius to Kelvin Celsius to Kelvin ConversionsConversions

• The The differencedifference between the Kelvin between the Kelvin and Celsius scales is and Celsius scales is 273273 increments, increments, so 0° C is 273 K and 100° C is 373 K.so 0° C is 273 K and 100° C is 373 K.

• To convert from Celsius To convert from Celsius toto KelvinKelvin, , addadd 273.273.

• From Kelvin From Kelvin toto CelsiusCelsius, , subtractsubtract 273. 273.

• 1212 C = ______ K 12 C = ______ K 12 C C + 273+ 273 = = 285285 K K

• 273 K = ______273 K = ______C 273K C 273K – 273– 273 = = 0°0° C C