Download Inv 14

Name____________KEY___________________ Date__11/21/14___ Partner(s)_________________________
_________________________
Investigation 14
Electric Circuits
I.
Complete circuits
A.
Use one battery, one light bulb, and one piece of wire. Connect these together in a variety of ways.
Sketch each arrangement below.
Arrangements that do light the bulb
Arrangements that do not light the bulb
Every other connection except
for those shown
Every other connection except
for those shown
You should have found four different arrangements that light the bulb. Examine the arrangements
that light and do not light the bulb. State the requirements that must be met in order for the bulb to
light.
THERE MUST BE A COMPLETE PATH FOR THE CURRENT
FROM, ONE END OF THE BATTERY TO THE OTHER. THE
COMPLETE PATH MUST TRAVEL THROUGH THE BULB FROM
THE BASE TO THE SIDE SCREW PART OF THE BULB.
B.
When a student briefly connects a wire across the terminals of a
battery, the wire feels warm. Why does the wire get warm?
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1
2
THE WARMTH IS DUE TO THE HEATING OF THE WIRE
CAUSED BY THE CURRENT FLOWING THROUGH THE WIRE.
The student finds that the wire seems to be equally warm at points 1, 2, and 3. Based on this
observation, what might you conclude about the amount of current flow at each place in the wire?
THE HEAT IS DUE TO THE CURRENT. IF THE HEATING IS THE SAME AT POINTS 1, 2, AND 3,
THEN THAT MEANS THAT THE CURRENT IS THE SAME AT THOSE POINTS.
C.
Light a bulb using a battery and a single wire (One of your connections in part I, A.). Observe and
record the brightness of the bulb when objects made out of various materials are inserted between the
bulb and the battery. Try materials such as paper, various coins, pencil lead, eraser, your finger, etc.
bulb lights
bulb does not light
PENNY
PAPER
NICKEL
ERASER
ETC.
ETC.
What is similar about the objects that let the bulb light?
ALL ARE METALS
D.
II.
Single Bulb Circuit
A.
The diagram shows a circuit with a single battery and a single bulb. Note that a
complete and unbroken path is present that allows electrons to flow from the
negative end of the battery, through the bulb, then back to the battery entering
the positive end. Because there is only one path for the electrons, the electron flow
or the electric current is the same at all points in the circuit. That is, the amount of
current flowing past point A is the same as flowing past point B, and is also the
same flowing through the bulb.
B.
filament
Carefully examine a bulb. Two wires extend from the filament of the bulb into
the base. You probably cannot see into the base, however, you should be able
to make a good guess as to where the wires are attached. Draw where the
wires attach.
glass or
ceramic
A
B
The strength of the current depends on the impeding effect of the bulb – its resistance. If the
resistance increases, then what happens to the current flow?
CURRENT FLOW DECREASES
C.
If the current through the bulb is large, then that means a lot of energy is being delivered to the bulb
by the electron current. Will the bulb be brighter when the current is large or when the current is
small? Explain.
THE BULB WILL BE BRIGHTER WITH A LARGE CURRENT. THE MORE ENERGY DELIVERED,
THE MORE ENERGY MUST BE DISSIPATED – IN THIS CASE AS HEAT AND LIGHT.
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A
III. Bulbs in series
A two-bulb circuit with identical bulbs connected one after the other as shown.
Bulbs connected in this way are said to be connect in series.
A.
B
Notice that there is only one path for the electrons to take going from the
negative end of the battery, through the bulbs, and then back to the battery.
1.
In this circuit, is the current the same flowing past points A, B, and C? Do
you know why?
C
THE CURRENT IS THE SAME. THERE IS ONLY ONE PATH FOR THE
CURRENT.
2.
As a result of inserting a second bulb, does the resistance to the flow of current increase, decrease
or remain the same?
THE RESISTANCE IS INCREASES.
3.
In this case, does the current increase, decrease, or remain the same?
THE CURRENT DECREASES.
4.
If the brightness of the two bulbs is compared, then their brightness’s will be the same. Why?
BOTH BUBS HAVE THE SAME CURRENT PASSING THROUGH THEM.
5.
If you were to unscrew one of the bulbs from the circuit, what do you think will happen? Why?
THE CURRENT WILL STOP FLOWING. IT’S NECESSARY TO HAVE A COMPLETE AND
UNBROKEN PATH FOR CURRENT TO FLOW.
B.
We know that a bulb causes an impeding effect (or resistance) to the current in the circuit.
1.
Thinking of the bulb in this way, would adding more bulbs in series cause the impeding effect
(or total resistance) to increase, decrease, or remain the same as before.
THE IMPEDING EFFECT (OR RESISTANCE) WILL INCREASE.
2.
Formulate a rule for predicting how the current coming from the battery would change (i.e.,
whether it would increase, decrease, or remain the same) if the number of bulbs connected in series
were to be increased.
AS THE NUMBER OF BULBS IN SERIES INCREASES, THE CURRENT WILL DECREASE.
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IV. Bulbs in parallel
A
A two-bulb circuit with identical bulbs so that their terminals are
connected together is shown. Bulbs connected together in this way
are said to be connected in parallel.
A.
Notice that as the electron current leaves the negative end of the
battery, it reaches point B and divides, part going through the left
bulb and part going through the right bulb. Because the bulbs are
identical, we can assume the electron current through both bulbs is
the same and, therefore, the bulbs will be of the same brightness.
1.
B
If you were to unscrew the right bulb from the circuit, what will happen to the left bulb?
THE LEFT BULB WILL REMAIN LIT, AND ITS BRIGHTNESS WILL NOT CHANGE.
2.
If you screw the right bulb back in, its brightness will be the same as the left bulb, which means
that the current through both is the same. Where did the current come from?
THE CURRENT WAS SUPPLIED BY THE BATTERY.
4.
How does the amount of current coming from the battery when connected to a single bulb
compare to the current coming from a battery when connected to a two bulbs in parallel? (More
current delivered, less current delivered, or the same amount of current delivered?)
MORE CURRENT IS DELIVERED BY THE BATTERY WHEN CONNECTED TO TWO BULBS
IN PARALLEL.
5.
How does the current coming from the battery change (i.e., whether it would increase, decrease, or
remain the same) if the number of bulbs connected in parallel were increased?
THE CURRENT COMING FROM THE BATTERY WILL INCREASE AS THE NUMBER OF
BULBS INCREASES.
6.
How does the resistance of the circuit change (i.e., whether it would increase, decrease, or remain
the same) if the number of bulbs in parallel were increased?
THE RESISTANCE OF THE CIRCUIT DECREASES AS THE NUMBER OF BULBS
INCREASES.
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V.
Circuits – Conclusions
Circuits consisting of bulbs (resistances) can be connected to batteries in series or in parallel (or in any
combinations of series and parallel).
As we connect more and more bulbs in series to a battery, we know that the total resistance of the
circuit ______INCREASES_____________(increases, decreases, or remains the same), and the current
delivered by the battery _____DECREASES_________(increases, decreases, or remains the same).
As we connect more and more bulbs in parallel to a battery, we know that the total resistance of the
circuit ____DECREASES_______________(increases, decreases, or remains the same), and the current
delivered by the battery ___INCREASES____________(increases, decreases, or remains the same).
VI. Application of These Ideas to Your Home Electrical Circuits
The batteries in the circuits described above act very much like the voltage sources supplied to your home
by the electric company, except that the batteries deliver DC and the electric company delivers AC. This
voltage supplies the energy needed to power the electrical devices in your home. The bulbs in the above
investigation act like the electrical devices in your home.
A.
From what you found in this investigation, do you think that the electrical devices in your home are
connected in series or parallel? How do you know?
THE ELECTRICAL DEVICES IN MY HOME ARE CONNECTED IIN PARALLEL. I KNOW THIS
BECAUSE WHEN ONE ELECTRICAL DEVICE IS TURNED OFF (DISCONNECTED),THE OTHER
ELECTRICAL DEVICES REMAIN ON.
B.
Why is it dangerous to connect too many lights and electric devices to one electrical circuit?
AS THE NUMBER OF ELECTRICAL DEVISE ARE CONNECTED TO A CIRCUIT INCREASES,
MORE AND MORE CURRENT MUST BE DELIVERED. WHEN THIS HAPPENS, THE CURRENT
CAN BECOME SO LARGE THAT THE WIRE BEGINS TO MELT AND BURN THE INSULATION
(AND POSSIBLY THE HOUSE).
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