Grade 9 Science ­ Chapter 9.notebook

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Grade 9 Science

Unit 2: Characteristics of ElectricityChapter 9

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Series Circuits In a series circuit, there is only one path for the current to travel

Bulbs connected in series: when one goes out, they all go out

Like the lights on your Christmas tree!!

As you add more bulbs, the brightness of the bulbs decreases because the voltage is affected

Adding more bulbs increases the resistanceand in turn decreases the total currentin the circuit

Grade 9 Science ­ Chapter 9.notebook

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Series Circuits

Nov 29­8:46 AM

Parallel Circuits A parallel circuit is a circuit with several different paths

Bulbs connected in parallel: when one goes out the others areunaffected

The lights in your house!!!

As you add more bulbs, the brightness is unaffectedbecause the voltage is unaffected

Resistance does not increase ‐ adding resistors (bulbs) in parallel will decrease the total resistance, this will increase the total current leaving the battery

No current is created or destroyed,only split up!

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Parallel Circuits

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Series Circuit Parallel Circuit

# of Pathways Single Multiple

Effect of removing a load

All the bulbs stop working: a break in the

circuit

All bulbs continue working: no break in

circuit

Voltage DropIncrease # of bulbs = decrease in voltage

Increasing bulbs has no effect on voltage

CurrentIncrease # of bulbs = decrease in current

Increase # of bulbs = increase in current

ResistanceIncrease # of bulbs = increase in resistance

Increase # of bulbs = decrease in resistance

Connecting cells to form a battery

Voltage increases to the sum of the voltage in the

cell

Voltage remains the same as the voltage in individual cells

Series vs. Parallel Circuits Page 294

Grade 9 Science ­ Chapter 9.notebook

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Series vs. Parallel Circuits Series ex: Flashlights

Parallel ex: Lighthouse

Flashlight cells are connected in series, this gives them a higher voltage (why?), which increases the current, which makes the bulb brighter

But what happens if one cell burns out??

Parallel connections are used when it is difficult to assess the circuit to change a battery or make repairs. In lighthouses the bulbs need to work for a long time and have low maintenence. Therefore, we use a parallel circuit so that the bulbs aren't as bright and will help the battery and the bulbs last longer!!

Nov 29­9:38 AM

Technologies for Safe Use of ElectricityCircuit Breakers: Act as a switch that can cut off all the power coming into your house

Fuses: Contains a metallic conductor that melts when excessive current heats it up

Grounding Terminals: allows excess current to flow in to the ground instead of giving you the shock

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Electrical EnergyElectrical Energy: the ability to do work, measured in Joules (J)

Electrical energy costs depend on 3 factors:1) Voltage Drop: describes how the supplied energy by the source (battery) is reduced as the electric current moves through the other elements of the circuit ‐ Electric Potential Difference2) Electrical Current3) Time

Electrical Power: the rate of change in electrical energy OR the rate at which work is done or energy is transformed, measured in Watts (W)

Power Rating: a measurement of how much electrical energy an electrical device consumes every second it is in use

Dec 2­8:23 AM

Calculating Power, Voltage, and Current

V

P

I

Let's use our trusty triangle!!

V = voltage (V)

P = power (W)

I = current (A)

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Calculating Energy Consumption

E

P t

Let's use our trusty triangle!!

E = energy transferred (J)

P = power (W)

t = time (s)

Bookwork: Read Calculating Energy Consumption on page 308 and then do the 3 Practice Problems

Dec 4­8:19 AM

Activity 9‐2B on Page 310

Page 313: 1‐7 & 9‐11

Kilowatt‐HourWhen talking about electrical energy used, we often hear or see kilowatt‐hours being used rather than joules. This is because a joule is a very small unit (1 watt x 1 second)

A kilowatt‐hour is 3 600 000 times larger than a joule

1 kilowatt‐hour is equal to 1 kilowatt (1000 watts) times 1 hour (3600 seconds)

The unit for kilowatt‐hours is kWh (yes, it has to be written this way!!!)

E

P t

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Electrical EfficiencyElectrical energy may be converted into other forms such as:

1) Light2) Heat3) Sound

Efficiency is the percent (%) of energy that is converted to a useful form

Efficiency = useful energy output total energy input

We have to realize that fluorescent bulbsare more efficient than incandescent bulbs

Do the practice problems on page 318and 319

x100

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EnerGuide LabelsEnerGuide Labels details how much energy an appliance uses in a year and compares to other appliances

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Reducing Electrical Consumption

Ways that we can reduce the amount of electricity we consume are:

‐ Improve insulation in the home‐ Turn off lights when not in use‐ Use energy efficient light bulbs‐ Air dry clothes when possible

Remember the STSE?? Electricity Conservation: The New Trend

Dec 3­10:59 AM

Energy GeneratorsElectrical Generators are made up of a coil of wire and a magnet

Electrical GeneratingStations

1) Hydroelectric2) Thermal3) Nuclear

Getting Power...

Transformers areelectrical devices that change voltage so thatit can be used byhomes (120V and 240V)

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Problems??1) Safety2) Cost of production3) Degree of environmental impact

Alternate Energy Sources‐ Wind generators‐ Solar energy‐ Fuel cells

Constraints on Alternates:‐ Cost‐ Availability of materials‐ Properties of materials

Read pages 330‐334 for more information

Bookwork: Page 336‐337 ‐ all questions