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INVESTIGATING ELECTRIC CIRCUITS
OP 49 - 53
Investigation 1
The effect on current of adding bulbs in a series circuit
Apparatus 60 mA bulbs, 6 V battery/ power supply unit, switch, leads, ammeter
1.
Build the circuit shown in the diagram.
Ammeter
A
Switch
Bulb
Battery
2.
Close the switch. Record the current.
_______________________________________________________________________
3.
Predict the value of the current if you place a second bulb in series in this circuit
_______________________________________________________________________
4.
Build the circuit and test your prediction. Record the current.
_______________________________________________________________________
A
Ammeter
Ammeter
Bulb 1
Switch
Switch
Bulb 2
Battery
Battery
5.
Was your prediction correct? Explain. ________________________________________
_______________________________________________________________________
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Investigation2
Measuring voltages in a parallel circuit
Apparatus 60 mA bulbs, 6V battery / power supply unit, switch, leads, voltmeter
1.
Build the circuit shown in the diagram. Bulbs connected in this way are said to be in
parallel.
Switch
Battery
Bulb 2
Bulb 1
V
Voltmeter
Fig 3
2.
Close the switch. What do you notice about the brightness of the bulbs?
_______________________________________________________________________
3.
Gently unscrew bulb1. What effect, if any, does this have on the brightness of bulb 2?
_______________________________________________________________________
4.
Replace bulb 1 and gently unscrew bulb 2. What effect, if any, does this have on the
brightness of bulb 1?
_______________________________________________________________________
_______________________________________________________________________
5.
Replace bulb 2. Measure and record the voltage across the battery. __________________
6.
Predict the voltage reading across bulb 1 and explain your prediction.
_______________________________________________________________________
_______________________________________________________________________
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7.
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Predict the voltage reading across bulb 2 and explain your prediction.
_______________________________________________________________________
_______________________________________________________________________
8.
Measure and record the voltages across both bulbs.
Vbulb1 = _______________
9.
Vbulb2 = ____________________
If you predicted incorrectly, can you now explain your results?
_______________________________________________________________________
_______________________________________________________________________
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Investigation 3
Measuring currents in a parallel circuit
Apparatus 60 mA bulbs, 6 V battery / power supply unit, switch, leads, ammeter
1.
Build the circuit shown in the diagram. (bulbs in parallel).
A
Ammeter
Switch
Battery
Bulb 2
Bulb 1
Fig 4
2.
Close the switch.
3.
Measure and record the current from the battery: _______mA.
4.
Would you get the same reading if you placed the ammeter on the other side of the
battery? ________________________________________________________________
If you are unsure check it out.
5.
On the circuit diagram mark the position with an X where would you place the ammeter
to measure the current in bulb 1?
_______________________________________________________________________
6.
Predict what current you would expect in bulb 1.
_______________________________________________________________________
7.
Place the ammeter in the correct circuit position to test your prediction.
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8.
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Predict what current you would expect in bulb 2 and state why.
_______________________________________________________________________
9.
Place the ammeter in the correct circuit position (marked with a Y) to test your
prediction.
10.
Explain why your prediction was either correct or incorrect.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
11.
Add another bulb in parallel and predict the total current in the circuit. Test and record
your prediction.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
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