Circuits are designed to control the transfer

of Electrical Energy

Chapter 9:

Page

1 path 1 path several pathsseveral paths

SERIES vs PARALLEL

One bulb goes out they ALL go out!

One bulb goes out they ALL go out!

One bulb goes out the others do NOT!

One bulb goes out the others do NOT!

SERIES PARALLEL

SERIESSERIES PARALLELPARALLELThe sum of the

Voltages lost on the loads equals the Total voltage supplied by the source

Vsource = Vloads total

The sum of the Voltages lost on the loads of a single path equals the total voltage supplied by the source

VOLTAGE

SERIESSERIES PARALLELPARALLELCells in series

increase voltage but battery life is shortened

Cells in parallel keep same voltage as single cell but battery life is lengthened

CELL EFFECTS

SERIESSERIES PARALLELPARALLEL

Same throughout Pathways differCurrent entering a

junction point = current leaving

Highest current on paths with less resistance

CURRENT

SERIESSERIES PARALLELPARALLEL

Resistors in series increase total resistance (therefore current I decreases – slows down flow)

Resistors in parallel will decrease the total resistance of the circuit (therefore current increases-faster flow)

RESISTANCE

Protecting Household Circuitspage 296

CIRCUIT BREAKERSBimetallic strip heats up and bends to prevent excessive current from entering the home

FUSEContains a metal conductor which melts when excessive current runs through it and thus breaks the circuit. It needs to be replaced to restart the circuit.

GROUNDING TERMINALS

The round prong on an electrical plug, prevents shock by allowing excess current to flow to the ground

RESISTORS IN SERIES AND PARALLEL

LAB 9-1F PAGE 300

Core Lab

Electrical Energy

-the ability of moving electrons to do work

- measured in Joules (J)

Section 9-2 page 304

The Power of Electricity

Video clips

ELECTRICAL POWER

POWER How fast Energy

changes from one form to another

heat E

electrical E light E sound E

Measured in watts (W)

1W = 1J/1s

Electrical Energy Costs

Depends upon 3 factors

1.Voltage Drop

2.Electrical Current

3.Time

POWER RATING

A measurement of how much electrical energy an electrical device consumes per second of use

Calculating Energy Consumption

E = energy (J)P = power (W)t = time (s) E

P t

E = ? P = 60 W

t = 25 min E = Pt

Convert time to seconds: t = 25 min x 60 sec = 1500 sec

1 min

E = (60 W)(1500 sec) = 90,000 J or 9 x 104 J

Example: How much electrical Energy is consumed by a 60W light bulb if it is left on for 25

min?

A LARGER Unit for Energy

Recall:1 Joule = 1 Watt × 1 second

For home usage increase W to kW and sec to hr

New larger units: kW∙h kilowatt-hour

Energy labels on appliances are in kW∙h

To calculate the cost of electrical usage in the home:

Multiply the kW∙h used by the rate charged by the electrical

company per kW∙h.

Current rate = $0.10/kW∙h

COST OF ELECTRICITY

Cost = (energy rating)(rate per kW∙h)

Stove A=(504 kW∙h)($0.10/ kW∙h)=$50.4 a year

Stove B=(735 kW∙h)($0.10/ kW∙h)=$73.5 a year

Stove A is more energy efficient!

Example: Which will save you more money on your yearly electrical bill, stove A which

has an energy rating of 504 kW∙h or stove B with a rating of 735 kW∙h per year of

average use?

Efficiency is the % of energy that is converted to a useful form.

Efficiency = useful energy output × 100% total energy input

Section 9.3 page 314

Electrical Energy in the Home

Efficiency = E output x 100% E input

= 4500J x 100% 7000J

=64.3%

The bulb has an efficiency of 64.3 %

Example: How efficient is a bulb that uses 7000 J to produce 4500J of light?

EnerGuide Labels

Details how much energy an appliance uses in a year in kW∙h and compares to other appliances

Electricity and the Environment

Section 9.4 Page 324

MECHANICAL ENERGY is energy of motion, it requires moving parts

A GENERATOR converts Mechanical Energy into

Electrical Energy

Examples include: Windmills, Hydroelectricity, Geothermal power, Nuclear power

A GENERATOR consists of a coil of wire and a magnet - one moves in relation to the other to generate

electricity

3 Types of Generators:

1. Hydroelectric –uses falling WATER to turn a turbine

2. Thermal Energy – uses heat from BURNING FOSSIL FUELS to boil water and the resulting steam turns a turbine

3. Nuclear Energy – uses heat from a NUCLEAR REACTION to boil water and the steam turns a turbine

The electrical energy generated is transmitted over LARGE distances using HIGH voltage and low current.

How does Electricity get to our homes?

Electrical device that changes voltage

Step UP increase voltage for transmission

and

Step down decrease voltage for use in our homes where it is provided as 120V and 240V

service.

Transformers

When Deciding what Energy source are appropriate for an area, several factors need to be considered:

SafetyCost of production

Degree of environmental

damage

Wind Energy

Solar Energy

Fuel Energy

Alternate Energy Sources include:

1. COST

2. AVAILABILITY OF MATERIALS

3. PROPERTY OF MATERIALS

New Energy Development is Limited by such factors as: