l10_simple_circuits.doc

7/24/2019 l10_simple_circuits.doc

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Name_________________________________

Topics covered in this lab:

Circuits

Electric Current

Conductivity

Experiment 1: Single Bulb Circuits

Materials: Flashlight battery Light bulb

Wire

We begin our study of electric circuits by connecting a battery and a bulb together and

observing what happens We investigate the conditions under which the bulb lights

brightly! dimly or not at all

"btain one battery! one light bulb! and one wire Connect these in as many ways as you

can #$etch each arrangement on the ne%t page "n one side of the page! listarrangements in which the bulb lights "n the other side of the page! list arrangements in

which the bulb does not light

&ou should ma$e s$etches of at least four different arrangements that light the bulb 'oware they similar( 'ow are they different from arrangements in which the bulb fails to

light(

)se the space below to state what re*uirements must be met in order for a bulb to light

+iscuss as a class

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ARRANGEENTS T!AT ARRANGEENTS T!AT

"#G!T T!E B$"B %&N'T "#G!T T!E B$"B

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Experiment (: A odel )or the Electric Circuit

Materials:

./ 0attery

Light bulbs 'eavy hoo$up wires

1hin wire

2n arrangement of a bulb! battery and wire that allows the bulb to light is said to be aclosed electric circuit 1he terms complete circuit! or 3ust circuit are also used 1he word

4circuit5 was originally used to mean 4a circular route or course5

6n wor$ing with electric circuits! you may have noticed some regularity in the way theybehave 7erhaps you have begun to form a mental picture! or a model! that helps you

thin$ about what is happening in a circuit 6n this e%periment! we will begin the processof developing a scientific model for an electric circuit

2 scientific model is a set of rules that applies to a particular system that ma$es itpossible to e%plain and predict the behavior of that system We would li$e to build such a

model for electric circuits that will enable us to predict the behavior of any circuit of

batteries and bulbs 6f we connect several bulbs and batteries together in a circuit! we

would li$e to be able to predict which bulbs will light! which will be brightest! dimmestand so forth

Activit* 1:0riefly connect the terminals of a battery +ith the thin +ireuntil the wire

feels warm %on't maintain this connection )or more than , seconds at a time sincethe +ire +ill get ver* hot-+oes the wire seem to be the same temperature along itsentire length or are some sections warmer than other( What might this observation

suggest about what is happening in the wire at one place compared to another(

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Now ma$e a single bulb circuit using the ./ battery and hoo$9up cables you have been

provided #$etch your circuit below #how the wor$ing circuit with the bulb lit; to the

instructor before moving on Note the brightness of the bulb

When a wire or a light bulb is connected across a battery! we have evidence thatsomething is happening in the circuit 1he wire becomes warm to the touch< the bulb

glows 6n constructing a model to account for what we observe! it is helpful to thin$ interms of a flow around a circuit We can envision the flow in a continuous loop from one

terminal of the battery! through the rest of the circuit! bac$ to the other terminal of the

battery! through the battery! and bac$ around the circuit We have found that a light bulbincluded in this circuit will light

.e shall assume that the brightness o) the bulb is an indicator o) the amount o) )lo+

through the bulb- Brighter means more )lo+ /though 0t+ice as bright does not

necessaril* mean t+ice the )lo+2-

1he assumptions that something is flowing through the entire circuit including the bulb;and that a light bulb can be used as an indicator of the flow are both consistent with our

observations

Follow9)p =uestion:

, Can you tell from your observations thus far the direction of the flow through thecircuit( Why or why not( Can you thin$ of any way you might be able to figure

this out(

+iscuss the above activity as a class

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1here is a standard way to draw diagrams that represent electrical circuits #hown below

is a circuit diagram for a bulb attached to a battery:

Notice that the diagram indicates the way in which things are connected: 2 wire goes

from one side of the battery to one terminal on the bulb 2 second wire goes from the

other side of the battery to the other terminal on the bulb Wire up a circuit in this wayand verify that the bulb lights up

Consider the following dispute between two students:

#tudent ,: 4When the bulb is lit there is aflow of electric current from the battery to

the bulb. There is also an equal flow of

electric current from bulb back to thebattery5

#tudent -: 4There is only flow from the

battery to the bulb. We know this is sobecause a battery can light a bulb, but a

bulb cant do anything without a battery5

+o you agree with student , or student -( E%plain your reasoning +iscuss as a class

batterybulb

wire

wire

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Activit* (: #et up a circuit having two bulbs

connected one after the other! as shown inthe diagram to the right When bulbs are

connected one after the other in this way

they are said to be inseries

Compare the brightness of the two bulbs 7ay attention to large differences only @ small

differences may be due to the fact that no two bulbs are e%actly the same:

Compare the brightness of each of the bulbs in the above circuit with the brightness of the

bulb in the single bulb circuit of 2ctivity ,

#witch the order of the bulbs in the above circuit and see if this ma$es any difference:

6f one of the bulbs is unscrewed! what happens to the brightness of the other bulb(

'ow does the amount of electric current that flows from the battery in the series two bulbcircuit compare with the amount of electric current that flows from the battery in the

single bulb circuit( E%plain your reasoning +iscuss as a class

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Activit* 3: #et up a two9bulb circuit having the

terminals of the bulbs attached together as shown

in the diagram to the right When bulbs areconnected in this way they are said to be

connected inparallel

Compare the brightness of the two bulbs:

Compare the brightness of each of the bulbs in the above circuit with the brightness of the

bulb in a single bulb circuit:

#witch the order of the bulbs in the above circuit and see if this ma$es any difference:

6f one of the bulbs is unscrewed! what happens to the brightness of the other bulb(

'ow does the amount of electric current that flows from the battery in the parallel twobulb circuit compare with the amount of electric current that flows from the battery in the


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'ow does the amount of electric current that flows from the battery in theparalleltwo

bulb circuit compare with the amount of electric current that flows from the battery in the

seriestwo bulb circuit( E%plain your reasoning +iscuss as a class

6t sometimes helps to thin$ of the flow of electricity in wires and bulbs as being similar

the flow of water through pipes 6n this picture! a wire behaves li$e a big fat pipe throughwhich water flows very easily! and a bulb is li$e a s$inny pipe through which water flows

more slowly 6n the same way! electric current flows very easily through the wires used

when hoo$ing up a circuit! but faces more resistance when flowing through a bulb

&ou can thin$ of a battery as a pump 2 water pump pushes water through pipes by

creating pressure 2 battery pushes electric current through wires and bulbs by creating a

voltage Bust li$e pressure is a measure of how hard a pump can push water! voltage is a

measure of how hard a battery can push electric current

Notice that you need the water pipes to ma$e a complete 4circuit5 in order for water to$eep flowing &ou also cant have any lea$s 1hese things are true in electric circuits also:

&ou need a circuit for electricity to flow! and you cant 4lea$5 electricity anywhere

1o ma$e water flow through a narrow pipe we need pressure 6f we increase the pressure

we increase the flow 6f we ma$e the narrow pipe longer! its harder for the water to

move! and the flow becomes smaller

6n the same way! to ma$e electric current flow through a lamp we need voltage 6f we

increase the voltage we increase the flow and the lamp becomes brighter 6f we put two

lamps one after the other it becomes harder for current to flow! and the lamps becomedimmer

For electric circuits this is summariDed by Ohms Law:I = V/Rwhich says that thecurrentIthrough any part of a circuit is e*ual to the voltage Vpushing across that part of

the circuit divided by the resistanceRof that part of the circuit esistance is 3ust a

measure of how hard it is for current to flow li$e the s$inniness of the pipe;! and we will

investigate this more in E%periments 8 and >


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Activit* 4: &ou are about to set up the three9bulb circuit

shown in the diagram to the right

0efore connecting the circuit! thin$ carefully and answer

the following *uestions:

,; 7redict what you e%pect brightness of each of the three

bulbs 2! 0 and C; will be compared to each other

2 and 0:

2 and C:

0 and C:

'oo$ up the circuit! observe the brightness of the three bulbs! and compare them:

2 and 0:

2 and C:

0 and C:

E%plain in words how you thin$ the electric current flows through your circuit in order to

e%plain your observations 6t may help to thin$ of the water analogy

'ow does the amount of electric current that flows from the battery in the three bulbcircuit compare with the amount of electric current that flows from the battery in the


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Experiment 3: #nvestigating Resistance

Materials:

./ 0attery

Light bulbs 'oo$up Wires

/arious materials

)sing the materials provided! design a circuit that you thin$ could be used to compare the

resistance of various materials #$etch your idea below and tal$ to your 12 before going

any further

Classify your materials into different categories according to their effect on the bulb

Ma$e a list of the ob3ects in each category 2n ob3ect that allows the bulb to glow brightly

is called a conductor 2n ob3ect that ma$es the bulb go out is called an insulator

C&N%$CT&RS #NS$"AT&RS

What do most ob3ects that let the bulb light have in common( +iscuss as a class

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Experiment 4: Can Electricit* 5lo+ #n solutions6

Materials: ./ 0attery

Light bulbs

'oo$up Wires +istilled Water

#alt! sugar I ba$ing soda

2s in E%periment 8! design and build a circuit to compare the resistance of various

materials 1his time you are getting ready to dip the ends of the wires into various

solutions What do you thin$ will happen( +iscuss it with your group and 12 and write

your predictions below

Now! dip the ends into a cup of distilled water +oes the light bulb light up( +oes thisagree with what you predicted(

Now add some salt to the water +oes the light bulb light up( Loo$ carefully at the

region of the water around the wires Write your observations below

&ou are about to repeat the steps above using sugar and then using ba$ing soda Which

do you thin$ will ma$e the water conduct electricity(

+o the e%periments and note your results below

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6s plain water a good conductor( 6s salty water a conductor( What in the salt creates a

conducting solution( +iscuss this with your group and e%plain your ideas below +iscussas a class

Why is it dangerous to use an electrical appliance with a sin$ or tub full of water near

you! even if that water came from the tap( )se your observations in this lab to help you

to answer this *uestion

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l10_simple_circuits.doc

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