Electricity

Part 2

Learning Objectives

• TLW know the impact of energy transfer and energy conversion in everyday life (TEKS 5)

• TLW evaluate, investigate and compare series and parallel circuits (TEKS 5.F)

Flow of Electricity• An electric charge has potential

energy• This potential energy is called

electrical potential energy• Electrical potential energy depends

on the position of the electric field• Remember – all charged objects

have an electric field

• Electrical potential energy = potential energy of a charged object due to its position in an electric field

• The electrical potential energy between two objects increases the closer they get

• The electrical potential energy decreases as the distance between two objects increase

Potential Difference• Potential difference is the change in

electrical potential energy of a charged particle

• The change occurs when a charge moves from one place to another in an electric field

• The SI unit for potential difference is volt symbol is (v)

• 1 volt (V) = 1 joule per coulomb

• Usually referred to as voltage

Batteries• A battery can convert chemical energy

into electrical energy• Batteries are sources of electrical

current because of the potential difference between the terminals

• One terminal is positive and one is negative

• This allows for an electrical current or the movement of charged particles

• Batteries range from 1.5V to 12V (car battery)

Positive Terminal

Negative Terminal

Flow of electrons• A voltage sets charges in motion• This creates a current = the rate at which

electric charges move• The SI unit for currents is ampere or amps –

symbol of i• Batteries are a direct current source

–Because the charges always move in the same direction (negative to positive)

• When the current is the movement of positive charges it is called conventional current

Resistance• Most electrical appliances in the US are designed for

the same voltage = 110 V– You have to use a converter if you travel to Europe

as they commonly use 220 V for appliances• But light bulbs come in different varieties

– So some are very bright and some are dim• Because they have different amounts of currents in

them (remember a current is the rate at which charges move)

• They have different currents because of their resistance

How Resistance works

• Resistance is caused by internal friction

• Friction slows the movement of charges down

• The filament in a light bulb is the resistance

–A 40 W light bulb has a higher resistance than a 100 W light bulb

More on Resistance

Review Vocab• Voltage – amount of potential energy that each

unit of electrical charge has (measured in volts - V)

• Current – rate of flow of electric charges (measured in amps - I)

• Resistance – measure of an objects ability to conduct electricity (measured in ohms – Ω - R)

• Power – measure of work done by electrical current (measured in watts – W)

Calculations• Resistance = voltage/current

R=V/I– The SI unit for resistance is ohm (Ω)

• Current = voltage/resistance

I=V/R– The SI Unit for current is amps (A)

• Voltage = current x resistance

V = I x R– The SI Unit for voltage is volts (v)

• Power = voltage x current

P = I x V– The SI Unit for power is watts (w)

Ohm’s Law• Ohm’s Law is a relationship between

voltage, current, and resistance

R

VI

Current (amps)

Voltage (volts, V)

Resistance (ohms, )More on Ohm’s Law

R

VI

V

I R

Magic Triangle for Electricity

Example 1A 1.5 volt battery is used in a flashlight that has a

light bulb with a 10 ohm resistor. How much current will flow through the light?

I = V .

R

I = 1.5 v

10 Ω

I = 0.15 A

Example 2A light bulb has 1 amp of current flowing through it

when a direct current of 10 volts is applied. What is the filament’s resistance?

R = V .

I

R = 10 v

1 A

R = 10 Ω

Example 3How much voltage does a battery have that

produces a current of 3 amps through a 3 ohm resistor?

V = I x R

V = 3 A x 3 Ω

V = 9 v

The Danger of Electric Shock

A CD player uses 2.5A

Electric Circuits

• Electric Circuits – a device that provides a complete pathway for the movement of charges

• A closed circuit = a complete path, creating current to flow

• An open circuit = no charge can flow, no current created

Parts to a circuit• Switch = allows the circuit to be open or closed;

“on or off”• Direct current source = creates the potential

difference; Ex. battery• Resistors = controls the current; how much is

flowing• Wire or conductors = connects the circuit

together• Electrical “object” = the reason for having the

circuit (the stuff you want to use/operate)

Schematic diagram• To draw a circuit a schematic

diagram is used

• Specific symbols represent each part of the circuit

Schematic Symbols• Direct Current source

• Switch

• Resistor

• Wire or conductor

• Bulb or lamp

Open

Closed

Series Circuit• A circuit that has only one path

for the electrons to take is called a series circuit

• If one object along the path is removed – the circuit will not work

• In a series circuit – the circuit either works or doesn’t

Parallel Circuits

• A circuit that allows electrons to flow through different pathways is called a parallel circuit

• If an object along the path is removed, the electrons can still flow through the circuit

• Most homes are wired on a parallel circuit

Fuses and Breakers• When too many things are “plugged

in” at one time, the circuit is overloaded

• This can lead to fires

• When worn out electrical cords are used – two wires may touch

–This creates another pathway for electrons to flow

–This is called short circuit

• Fuses are used to prevent circuit overload

• A fuse is a metal strip that melts when a current becomes too great

• ALWAYS find out why a fuse “blows out” before you replace it

• A circuit breaker acts as a switch

–A breaker is designed to open the circuit to prevent any more current from flowing

Independent Practice

• Calculations to determine voltage, current, and resistance

• Calculations to determine cost of electrical usage

Lab

• In Periodic Groups, read entire procedure for understanding– Lab to be assigned by teacher

• Set up experiment using scientific method

• Identify potential hazards, precautions to take, and any PPE needed