1C : ircuits checkpoints
1. What is electric current?
2. What units are used to measure current?
3. Which materials allow current to flow easily?
4. Which materials prevent the flow of electric current?
5. What is a circuit?
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1. What is potential difference (voltage)?
2. What is a battery?
3. How is the capacity of a cell measured?
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1. What is the direction of flow of conventional current?
2. Can the behaviour of electronic circuits be analysed by assuming current flow in this direction?
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1. Which part of the torch limits the flow of current?
2. What units are used to measure resistance?
3. What symbols are used to represent current, potential difference (voltage), and resistance?
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1. If the potential difference (voltage) across a wire is constant, reducing the resistance of the wire causes the current to . . . ?
2. If the potential difference (voltage) across a wire is increased, without changing its resistance, the current will . . . ?
3. Calculate the resistance of a lamp filament if 150 mA of current flow when the lamp is connected to 3 cells in series (4.5 V).
4. In the circuit below, which switches should be closed . . .
(A) to light lamp L1 only?
(B) to light lamp L2 only?
(C) to light lamps L1 and L2?
5. What would happen to lamps L1 and L2 if switches S1, S2 and S3 were all closed at the same time? Why should closing all three switches be avoided?
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1. What are the important features of ammeters, voltmeters and ohmmeters?
2. Which type of meter is used most often?
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1. A flow of charged particles, usually electrons.
2. Amps and milliamps.
3. Conductors, the metal parts of the torch.
4. Insulators, the plastic parts of the torch.
5. A closed conducting path.
back to CHECKPOINT A
1. The push provided by a cell or battery which causes current to flow. (It can also mean the difference in energy across the lamp.)
2. An arrangement of two or more cells connected in series or parallel.
3. In amp-hours, Ah, or milliamp-hours, mAh.
back to CHECKPOINT B
1. From positive to negative.
back to CHECKPOINT C
1. The thin wire of the filament.
2. Ohms, W, kilohms, kW, and megohms, MW.
3. I : current, V : voltage, R : resistance.
back to CHECKPOINT D
|3.||(150 mA=0.15 A)|
4. Switches which need to be closed . . .
(A) to light lamp L1 only: S1 and S3.
(B) to light lamp L2 only: S1 and S2.
(C) to light lamps L1 and L2: S1 only.
5. Both lamps would go out. Closing all three switches is a bad idea because this short circuits the power supply. A large current will flow and the cells will overheat and may explode!
back to CHECKPOINT E
1. An ammeter is used to measure current. The circuit must be broken so that the meter can be connected in series. An ammeter must have a very low resistance.
A voltmeter is used to measure potential difference. The circuit does not need to be changed because the meter is connected in parallel. A voltmeter must have a very high resistance.
An ohmmeter is used to measure resistance. The component must be removed from the circuit altogether for a measurement to be made.
2. A voltmeter (signals in electronic circuits usually produce voltage changes).
back to CHECKPOINT F
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