1.3.2

Voltage in Electrical Systems

Define electric potential, or voltage.Differentiate between AC and DC.Identify the most common source of DC

voltage.Describe how to connect DC voltage sources

so that voltage will be added.

Objectives

Recall that a field is a model used to help understand and predict how forces are transmitted from one object to another.

Electric field – electric force per unit charge.

q

FE E Unit is Newton per

Coulomb (N/C)

Click on this link to go to an electric field simulation from Phet

Potential energy – energy of a particle associated with its position.

Electrical Potential

When charges are within an electric field an electrical potential difference is created.

Volt – unit of measurement for potential difference. (electrical potential, voltage)

Voltage is the prime mover in electrical systems (like pressure in fluid system).

Electrical Potential

Gravitational potential difference – ability to accelerate a mass between two heights.

GPE = mgh

Electric potential difference (or voltage) – ability to accelerate an electric charge between two points in an electric field.

V = E dUnits: N•m, or J Units: N•m/C, or J/C (or Volt, V)

Electrical Potential

Fluid system Electrical system

Flow caused by “potential” difference

Current – Flow

Recall, pressure is a prime mover in fluid sytems.

Voltage is a prime mover in electrical systems.

The flow of charge is called current. Current continues until the plates are neutral.

Pump is used to maintain pressure difference.

A battery is used to maintain a potential difference.

Voltage source (battery or generator)Conductors (wires or circuit board)Load (motor, lights, etc.)Control element (switch)

Components of Electrical Systems (fig. 1.37)

Voltage source

Control

Electrical Load

Electrical circuit

Load – an appliance or machine.Conductor – material through which charge can

easily flow.Control element – a switch that turns the current

in the system on or off.Electrical circuit – closed path for current flow

created by connecting voltage sources, conductors, control elements, and loads.

Voltage source

Control

Electrical Load

Electrical circuit

Two types of current (or charge) in electrical systems:Direct current (DC) – current flows in one

direction.Produced by batteries

Alternating current (AC) – current flows back and forth many time each second.Produced by alternators

Direct Current and Alternating Current

Direct Current (DC) – charge flows in one direction.BatteriesSolar Panels

Alternating Current (AC) – charge flows back and forth.AlternatorsGenerators

AC vs. DC

Cell – single unit that houses on or more chemicals.Electrons and ions are separated in a cell

creating a voltage.Voltage depends on the chemicals used

(Table 1.6).Battery – a collection of two or more cells

connected together.Battery is “dead” when voltage drops

below that required to drive the load.Types of cells (Figure 1.38)

Primary cell – one-time use.Secondary cell – rechargeable.

Can be added by connecting cells in series, connecting the positive terminal from one cell to the negative terminal of the next cell.Individual voltages of each cell adds together

(Figure 1.39).In the circuit, electrons move out of the

negative terminal/electrode (or cathode) and enter the positive electrode (or anode)

Connecting Cells to Add Their Voltages

ELECTRICAL SYMBOLS

Wire

Switch

Lamp

Load

Battery

AC power

A Simple DC Circuit

DC circuit

Use this Phet web site link for DC Circuit Construction to download and practice making DC circuits.

Click on this Phet web site link for DC Circuit Lab to get more practice with DC circuits

Positive and negative terminals change many times per second.

Majority at a rate of 60 cycles per secondCycling rate, called frequency.Measured in hertz, cycles per second (1/s,

or Hz).

AC Circuits

AC Circuit Demonstration

Click on this Phet web link on AC Current – click on the link, download the program and practice making AC circuits

Click on this Phet web link for the AC Current Lab simulation.

Electric field

q

FE E

Unit is Newton per Coulomb (N/C)

221

d

qqKFE

• SI unit for charge is the Coulomb (C).

• Elementary charge of one electron or proton is 1.60 x 10-19 C

• q1 and q2 are the charges on two objects.

• d = distance between charged objects

• K = constant = 9.0 x 109 N•m2/C2

Electrical force

V = E x d

E = electric fieldd = distanceUnit is volts

Voltage

Net Voltage Vnet = Vf – Vi

E = V/d Unit is V/mElectric field

distance

d = V/E Unit is meters

Charge

# of electrons x elementary charge 1 electron

Unit is Coloumb

Direct currentTotal voltage is the sum of all voltage sourcesVt = V1 + V2 + V3….Battery + battery + battery – conductor (wire) – load – wire.

Alternating currentTotal voltage is difference between the voltage sources on each side of the load.Vt = V on side one – V on side 2

Battery – conductor – load – battery in reversed position - conductor

ELECTRICAL SYMBOLSWire

Switch

Lamp

Load

Battery

AC power