PSAA CurriculumPSAA Curriculum

UnitUnit

Physical Science SystemsPhysical Science Systems

Problem AreaProblem Area

Energy and Power SystemsEnergy and Power Systems

Generating an Generating an Electromotive ForceElectromotive Force

LessonLesson

What is needed to produce energy?What is needed to produce energy?

Can electricity be produced with two nails Can electricity be produced with two nails and a piece of fruit?and a piece of fruit?

MultimeterMultimeter

What electrical What electrical measurements can measurements can be taken with this be taken with this meter?meter?

What are some What are some practical uses for practical uses for these these measurements?measurements?

Learning ObjectivesLearning Objectives

Generate an electromotive force by means of chemicals, magnetism, heat, and solar radiation.

Construct a primary cell and understand its function.

Learning ObjectivesLearning Objectives

Explain the function of a voltmeter and construct a voltmeter circuit, which is the same type as used in commercial voltmeters.

Properly connect a voltmeter to a circuit and measure voltage in a circuit.

TermsTerms

Ammeters

Cell

Conductor

D’Arsonval meter movement

Electricity

Electromotive force

Electrons

Linear scale

Magnetic field

Multimeters

Nonlinear scale

Solar Cell

Square-law scale

Voltmeter

What different methods can be What different methods can be used to generate an electromotive used to generate an electromotive

force?force?Electricity is a form of energy present when electrons move through a complete path.

Electrons are negatively charged atomic particles that normally revolve around the nucleus of an atom.

The force that causes the electrons to move through the path is voltage or electromotive force.

The path the electrons follow through easily is a conductor.

What different methods can be What different methods can be used to generate an electromotive used to generate an electromotive

force?force?The most popular commercial method of generating an electromotive force is by means of magnetism.

A coil of wire has a moving magnetic field passed through it and thus produces an electromotive force.

This type of generation occurs in an alternator in an automobile or in the large generators used to produce electricity for the home.

MagnetismMagnetism

In 1820, Danish physicist, Hans Oersted discovered that a compass needle could be deflected by an electric current.

Until that time, it was generally thought electricity and magnetism were completely different.

Magnetism (cont.)Magnetism (cont.)

In order for there to be a reading on a voltmeter, for example, a force must act upon the charges that are moving along the magnetic field lines. If the charge is not moving or is moving in the

same direction as the magnetic fields, then there is no force.

But, if the charge is moving across the field lines, then the charge has force acting upon it and an electrical current can be measured.

Magnetism (cont.)Magnetism (cont.)

Hans Oersted showed that electricity can have an effect on magnetic fields, but it wasn’t until 1832 that Michael Faraday showed that magnetic fields could have an effect on electrical currents.

This is called the complementary effect and is demonstrated in this experiment.

What different methods can be What different methods can be used to generate an electromotive used to generate an electromotive

force?force?

Emf (electromotive force) by chemical reaction was discovered by Anastasio Volta who invented the first battery by discovering that certain combinations of metals produced an electromotive force.

Electromotive Force (Emf)Electromotive Force (Emf)

Emf by heat is demonstrated by the use of a thermocouple, a device that consists of the junction of two dissimilar metallic conductors, such as, copper and iron.

An emf is induced when the conductors are maintained at different temperatures.

Electromotive Force (Emf)Electromotive Force (Emf)

Emf by solar radiation is demonstrated by the photovoltaic cell.

This solar cell has the capacity to convert light directly into electricity without having a heat engine (defined as any device that changes thermal energy into mechanical work) involved.

Emf by magnetism was discussed earlier in this lesson.

Solar CellSolar Cell

What is a primary cell? How does a What is a primary cell? How does a cell generate electromotive force?cell generate electromotive force?

Chemical reaction is one of the six basic forms of energy (Others include friction, magnetism, pressure, heat, and light).

Chemical energy is converted into electrical energy by a device known as a cell.

Two or more cells connected form a battery.

Primary CellsPrimary Cells

Primary cells can be recharged using only new materials while secondary cells are rechargeable without replacing materials used to make the cell.

The lead-acid storage battery is a type of secondary cell.

How does a cell generate How does a cell generate electromotive force?electromotive force?

Each cell in the battery has two groups of coated lead plates known as electrodes.

The positive plate is made of lead peroxide and the negative plate is made of lead.

The electrodes are separated from each other and immersed in a liquid solution called an electrolyte.

How does a voltmeter function and How does a voltmeter function and how can we construct a voltmeter how can we construct a voltmeter

circuit?circuit?A voltmeter circuit contains a d’Arsonval meter (similar to a galvanometer) and an extremely high ohm resistor in series with the meter.

How does a voltmeter function?How does a voltmeter function?

A linear scale on the meter has readings divided into equal portions.

A nonlinear scale on the meter is marked off by uneven spaces.

Voltmeters indicate the amount of voltage present in the circuit, ammeters measure current flow through the conductor, and ohmmeters indicate electrical resistance.

How does a voltmeter function and How does a voltmeter function and how can we construct a voltmeter how can we construct a voltmeter

circuit?circuit?Multimeters are capable of measuring more than one characteristic of a circuit, i.e. voltage, amperage, and resistance. Multimeters usually show both linear and nonlinear scales. A square-law scale is a type of nonlinear scale which increases by squares. Each larger scale marking indicates that the measured value is multiplied by itself.

How does a voltmeter function and How does a voltmeter function and how can we construct a voltmeter how can we construct a voltmeter

circuit?circuit?d’Arsonval meter movement is the portion of the meter consisting of a fixed permanent magnet and a moving electromagnetic coil. The voltmeter is calibrated to show the amount of voltage which would cause an amount of current to flow through the carefully selected resistance of the voltmeter. The voltmeter is current sensitive. The extent of the movement of the meter pointer is directly proportional to the amount of current flowing through the meter.

How is a voltmeter used to properly How is a voltmeter used to properly measure voltage in a circuit?measure voltage in a circuit?

A voltmeter is always connected in parallel in a circuit.

It is put across a resistor or voltage source.

The multiplier resistor allows for varying degrees of accuracy when using a multimeter for ampere, ohms, and volt readings.

Connecting a Voltmeter in Connecting a Voltmeter in parallel to a test circuit. parallel to a test circuit.

What is a voltage drop?What is a voltage drop?

Voltage drops occur in power lines running from the transformer to the circuit box and in the wiring inside a building. A small amount of power is always lost as electricity flows through the wires.The energy loss is measured as voltage drop. The voltage drop is calculated by multiplying the current times the resistance.

Review/SummaryReview/Summary

What different methods can be used to What different methods can be used to generate an electromotive force?generate an electromotive force?

What is a primary cell?What is a primary cell?

How does a cell generate electromotive How does a cell generate electromotive force?force?

Review/SummaryReview/Summary

How does a voltmeter function and how How does a voltmeter function and how can we construct a voltmeter circuit?can we construct a voltmeter circuit?

How is a voltmeter used to properly How is a voltmeter used to properly measure voltage in a circuit?measure voltage in a circuit?

What is a voltage drop?What is a voltage drop?