Current ElectricityIntroductory Physics

Canadian Academy

Group Members A

Is this plausible Could you really power a house with static electricity

httpwwwyoutubecomwatchv=scUosAkxlvo

Current Electricity Construct and explain

Work in pairs or by yourself for these tasks With each question

bull Build it in the PhET simulationbull Build it in the lab if possiblebull Draw the circuit diagram and

answer the questions on the slide

httpphetcoloradoeduensimulationcircuit-construction-kit-dc

You should be able tobull Define current electricitybull Define resistance and state the factors that

affect resistance in a metal wirebull Define potential difference (voltage)bull Explain the effect of potential difference

and resistance on a currentbull Draw basic circuit diagrams involving

batteries lamps switches and wiresbull Define electrical power including the

relationship to voltage and current

Your finished work should be uploaded to SlideShare (or

Google Docs if it works) and embedded into a blog post

+ - + -

cell batterywire

junction

bulb lamp

cathode anode

switch

resistor

V A

voltmeter ammeter

Some basic circuit symbolsYou can use these to build the circuits on the next slides

What do these two components measure

electron flow

conventional current

Voltmeter measures the potential difference in charge between two points on a circuit while ammeter is used to measure the electrical current of a circuit

A

A simple series circuitDefine current electricity

bull It is a flow of electronselectrical charge and can be used to power objects (bulbs etc)

Label the direction of flow of electrons and the direction of the conventional current

bull Conventional currents incorrectly assume electrons flow from positive to negative (Shown in green arrow)

Use the non-contact ammeter to measure the current in the circuit

bull 090 amps

What happens if the cell is not included in the circuit Explain

bull Bulb is not lit because battery provides electron flow Chemical reactions in the battery causes electrons to build up and electrolyte prevents electrons from directly moving out from anode Instead when wires connect a path from cathode to anode electrons flow from the cathode (negative) to anode (positive)

Electrons flow from negative to positive but conventional current is the opposite (Shown with red arrow)

A

Switches and currentBuild this circuit

Measure the current with the switch in the open position

bull 0 amps

Close the switch and measure the current Explain your answer

bull 09 ampsBy closing the switch the circuit is completed and

allows electrons to flow as a current

Move the ammeter to different positions in the circuit and measure the current Does position matter

bull No electric flow remains constant

Are electrons lsquoused uprsquo in the circuit Are electrons lsquocreatedrsquo in the cell

Electrons can neither be created nor destroyed as reference to the Law of Conservation of Energy

A

Potential Difference (voltage)Modify the circuit to increase the potential difference by including two then three cells

What happens to the bulb bull The more cells the brighter the bulb

becomes

What happens to the current measurements 1 cell 09 amps2 cells 18 amps3 cells 27 amps

Explain your answers bull Batteries provide the electrical flow so with less

batteries there are less electrons to overcome resistance of bulb therefore reducing the amp reading

Define potential difference (voltage) bull It is the amount of energy per charge unit that is

needed for moving electrons to move through circuit

Complete the circuit diagram for three cells

Bulb

Resistance (incandescent bulbs or lamps)Go to the following applet and see resistance at a molecular level and how a light bulb workshttpmicromagnetfsueduelectromagjavafilamentresistance

Explain in your own words how moving charges cause a bulb to glow

The electrical flow moving from the battery through the light bulb creates collisions between the electrons of the flow and those of the bulb itself as well as atoms These impacts create resistance and as the electrons flow through the bulb this energy is used to light up the bulb (and also produce heat)

Resistance (incandescent bulbs or lamps)Build this circuit Add bulbs and record your observations

A

Bulbs (A) Observations

1 18 Bulb is very bright only one source of resistance

2 09 Bulbs create twice as much resistance therefore resulting amp reading is 18 divided by two

3 06 Bulbs create thrice as much resistance again causing the original (18) amp reading to be

divided by THREE now

4 045 Resistance of four bulbs create quadruple the amount of resistance so the amps generated for

one bulb is divided by four

5 036 Patternpatternpattern five times resistance= amps reading decreased by five times (18

divided by 5)Explain your findings in detail

There is an obvious pattern in that with eachadditional bulb the amp reading would decreaseproportionally to the increased resistance from bulbsTherefore the formula A=18B in which A equals the amp reading and B equals the number of bulbs can be used to demonstrate this inverse relationship So with increase of bulbs electron flow needs to overcome more resistance causing amps reading decreases

Remove all the bulbs to create a short circuit and measure the current if you can Explain There is very little resistance in the circuit therefore with the speedy movement of electrons it goes back to cell without being used in light bulbs etc therefore causing the electrons to heat up and cause a short circuit Resistance transforms energy to different types and uses some of it With no resistance no energy is used up and eventually heats up When it hits point of resistance in battery it causes frictional heat energy The amps reading was 1424861 amps

Conclusions Use your findings in the circuits so far to write your own Laws

Law of current in a loopldquoElectrons flow from negative to positive through the battery circuit must be completeldquo

Law of voltage and current (whatrsquos the relationship)

ldquo As the voltage increases within circuit current of electrons flows faster voltage is potential difference (what is the

mathematical relationship) Current = Voltage Resistanceldquo

Law of resistance and current (whatrsquos the relationship)

ldquo Potential difference (Voltage) is needed so that electrons can overcome resistance to flow in a circuit therefore the greater the resistance the less the current until resistance causes potential difference to reach 0 Resistance = Voltage

Current A good conductor lets electrons flow through smoothly while an insulators would cause greater resistanceldquo

Why is it dangerous to have too little resistance in a circuit

This would cause a short circuit See previous slide for more details This excessive electrical current can cause a rapid heat up of batteries fire and even explosion Someone could really hurt themselves

Parallel Circuits How many different routes can current take through this circuit

bull 2 routes

Close the lower switch only Observe the bulb and measure the current

bull

Close the upper switch only Observe the bulb and measure the current

bull 18 Amps

Close both switches Observe the bulbs and measure the current at different positions

bull 36 Amps

Observe the animation carefully What happens to the electrons at junctions -At junctions electron amps are divided by two to be equally distributed as energy to light the two bulbs therefore slowing electron flow until the second junction speeds electron flow again

Draw a circuit diagram for this set-up below

Law of Parallel Circuits

Law of parallel circuitsldquoWith each additional parallel path (and bulb) created the electron amps before the first junction

occurs gains 18 additional ampsldquo

Write your own Law based on observations

Now test your Law using a third bulb in parallel Draw the circuit diagram below and write your observations of the bulbs and of current

As my law predicted the number of amps before the first junction occurred was a 18 amp increase with the addition of 1 parallel path with a bulb As in my observations in the previous slide the electron amps were evenly distributed along the three circuit paths so that each bulb was fueled with the 54 amps divided by three 18 amps

More Parallel Circuits Close one switch at a time and record your observations

bull Bottom switch closed 09 amps bull Top switched closed 18 amps

Close both switches and record your observations bull Both switches closed 27 amps (before first

junction occurs)

Carefully observe the junctions What is happening Explain with reference to resistance and junctions Instead of 36 amps of electrical current as when two parallel circuits were made (with two bulbs on each path) only 27 amps were recorded This is because the first path (with the two bulbs) consists of a series circuit which means that both bulbs create greater resistance Originally 2 batteries can power a bulb using 18 amps of electrical current however in a series circuit the electrons need to overcome greater resistance with each added bulb Therefore with each additional bulb added in a series for this circuit the increasing resistance causes electrons to flow slowerdecreased amps The top path remains unaffected because of unchanged resistance thus the electrical current in this path is 18 amps Thus at the first junction the 27 amps of current split to provide the series path with 09 amps while providing the parallel path with 18 amps In this context parallel circuits are more efficient in using electricity

Do you need to modify your Law of Parallel Circuits

Draw a circuit diagram for this set-up below

Law of Parallel Circuits

Law of parallel circuitsldquo In the event that there is a series circuit occurring in one or more parallel paths of a parallel circuit those series paths will experience of a decrease of electrical flow proportional to the number of bulbs added in the series while

parallel paths with no series of bulbs always are charged by 18 amps (or

proportional to how many batteries are being used) ldquo

Modify your Law

As mentioned much earlier the inverse relationship between number of bulbs in a series circuit and amps of electrical charge can be expressed with the formula A=18B in which the number of amps are represented with variable A and B represents the number of bulbs However 18 assumes that the circuit contains two batteries

More ResistanceUse two cells and two bulbs in a circuit Use CTRL-click to adjust the resistance of the bulbs (one is 20 ohms (Ω) the other is 10Ω)

What is the difference between these two bulbs on a molecular levelbull The bulb with 10 ohms of resistance does not resist the flow of electrons in a circuit as effectively as the

bulb with 20 ohms of resistance Therefore the electrons of the current can move faster through the bulb and collide with the electrons and atoms of the bulb itself However in the bulb with 20 ohms of resistance there much more resistance experienced because electrons are more scattered This means that electrons from the current in a circuit cannot overcome the resistance as easily as the bulb with 10 ohms of resistance

Wire up the bulbs in two different circuits series and parallel Draw the circuits below Under each circuit record and explain your observations

Series Parallel

16

In the series circuit the bulb with greater resistance generated a brighter light than the bulb with 10 ohms less of resistance

Because the current remains constant between both bulbs the bulb with greater resistance needs to have a larger potential difference

In the parallel circuit the bulb with less resistance generated a brighter light than the bulb with 10 ohms more of resistance

Because the potential difference between both bulbs remains constant greater bulbs with lower resistance need to draw a larger current

Series

Parallel

Electrical PowerDefine electrical power and state its unit

bull It is the rate that electric circuit transfers electric energy Unit is in watts

What is the relationship between electrical power and lsquopowerrsquo as we have studied in the previous unit

bull Both are rates of using energy in a certain way Electrical power is the rate that an electric circuit transfers electric energy while the power studied in the previous unit refers to the rate that energy is used over time

Compare two methods of generating electrical power one fossil-fuel based and one renewable How do they work What are the benefits disadvantages of each

(See next page)

Electrical PowerDefine electrical power and state its unit

bull It is the rate that electric circuit transfers electric energy Unit is in watts

What is the relationship between electrical power and lsquopowerrsquo as we have studied in the previous unit

bull Both are rates of using energy in a certain way Electrical power is the rate that an electric circuit transfers electric energy while the power studied in the previous unit refers to the rate that energy is used over time

Compare two methods of generating electrical power one fossil-fuel based and one renewable How do they work What are the benefits disadvantages of each

(See next page)

18

Fossil-fuel based energy generation

PROSbull Cheaper than some renewable energy sourcesbull For example price for generating

electricity with black coal is around 2 yen per kilowatt hour compared to wind farm electricity which costs around 18 yen

bullCompact generators for easy portable usebull Natural gas oil coal etc

bullAbility to generate massive amounts of energy at a single place

bullPower plants that use gas tend to be super efficient

CONSbullEmission of carbon dioxide which pollutes the world causing the greenhouse effect and contributing greatly to global warming

bullBurning coal (also) causes sulfur to be released into the air which created acid rain

bullExtraction of crude oils can potentially be hazardous to underwater environment and create massive pollution if something like an oil spill were ever to happen (BP oil spill cough cough)

19

Renewable energy generation

PROSbullRenewable energy sources can be easily replenished and are not for one-time-use only

bull(Mostly) clean source for energy with no direct harm to environment like fossil fuel energy

bullPower plants generally require very few workers to operate which means low cost to operate and cheap maintenance

bullNo additional fuel costs such as for solar power and wind power

CONSbullNot always reliable and consistent in producing energybull Ie wind turbines may experience lack of

wind solar panels on a cloudy day

bullInvestment in setup before creation is high and costly

bullLimits to placementportability of generatorbull Hydropower near water solar power needing

sunny climate etc

ExtensionIf you finish with extra time

bull Check the Laws you have written against published information Do they concurbull Find out more about circuits and their components bull Find out about the difference between AC and DC

Direct currents (DC) describe currents that have a constant flow of electricity in one direction This kind of electricity can be produced from a battery in a circuit or a source with both positive and negative non-changeable terminals for electrons to travel through However alternating currents (AC) are currents with a changing flow of electrons This means that the source of electricity can either contain voltages that change from positive to negative polarity over time or can produce voltages with the ability to change polarity Therefore direct currents sustain current flow in one direction while alternating currents can change direction due to shifting polarity

In some aspects of using electricity AC and DC can both be used so AC may seem less useful For example when we use electricity to lessen a heat source the direction or charge of the current does not matter as long as the voltage and current are sufficient to produce the necessary heat But one important aspect of AC is that these currents are crucial to build electric generators motors or systems responsible for the distribution of power These devices run much more efficiently using AC than DC therefore AC is most commonly applied to projects requiring great amounts of electricitybull Build your own circuits and draw the circuit diagrams below

19

Renewable energy generation

PROSbullRenewable energy sources can be easily replenished and are not for one-time-use only

bull(Mostly) clean source for energy with no direct harm to environment like fossil fuel energy

bullPower plants generally require very few workers to operate which means low cost to operate and cheap maintenance

bullNo additional fuel costs such as for solar power and wind power

CONSbullNot always reliable and consistent in producing energybull Ie wind turbines may experience lack of

wind solar panels on a cloudy day

bullInvestment in setup before creation is high and costly

bullLimits to placementportability of generatorbull Hydropower near water solar power needing

sunny climate etc

ExtensionIf you finish with extra time

bull Check the Laws you have written against published information Do they concurbull Find out more about circuits and their components bull Find out about the difference between AC and DC

Direct currents (DC) describe currents that have a constant flow of electricity in one direction This kind of electricity can be produced from a battery in a circuit or a source with both positive and negative non-changeable terminals for electrons to travel through However alternating currents (AC) are currents with a changing flow of electrons This means that the source of electricity can either contain voltages that change from positive to negative polarity over time or can produce voltages with the ability to change polarity Therefore direct currents sustain current flow in one direction while alternating currents can change direction due to shifting polarity

In some aspects of using electricity AC and DC can both be used so AC may seem less useful For example when we use electricity to lessen a heat source the direction or charge of the current does not matter as long as the voltage and current are sufficient to produce the necessary heat But one important aspect of AC is that these currents are crucial to build electric generators motors or systems responsible for the distribution of power These devices run much more efficiently using AC than DC therefore AC is most commonly applied to projects requiring great amounts of electricitybull Build your own circuits and draw the circuit diagrams below

ExtensionIf you finish with extra time

bull Check the Laws you have written against published information Do they concurbull Find out more about circuits and their components bull Find out about the difference between AC and DC

Direct currents (DC) describe currents that have a constant flow of electricity in one direction This kind of electricity can be produced from a battery in a circuit or a source with both positive and negative non-changeable terminals for electrons to travel through However alternating currents (AC) are currents with a changing flow of electrons This means that the source of electricity can either contain voltages that change from positive to negative polarity over time or can produce voltages with the ability to change polarity Therefore direct currents sustain current flow in one direction while alternating currents can change direction due to shifting polarity

In some aspects of using electricity AC and DC can both be used so AC may seem less useful For example when we use electricity to lessen a heat source the direction or charge of the current does not matter as long as the voltage and current are sufficient to produce the necessary heat But one important aspect of AC is that these currents are crucial to build electric generators motors or systems responsible for the distribution of power These devices run much more efficiently using AC than DC therefore AC is most commonly applied to projects requiring great amounts of electricitybull Build your own circuits and draw the circuit diagrams below

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