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PHYSICS GRADE 12 REVISION 2008

WORK SHEET 10

1) A battery of negligible internal resistance is connected to a resistor network as shown. A current of 50mA is drawn from the battery.

Determine the reading of each of the three meters

(a) Reading on ammeter A:

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(b) Reading on Voltmeter V1

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(c) Reading on Voltmeter V2

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(d) Effective resistance of the resistor network.

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2) (a) A thick wire is connected in series with a thin wire of the same material and a battery. In which wire do the electrons have the greater drift velocity? Explain your answer.

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(b) A battery is connected in across a large resistor and a small resistor is connected in parallel. The current through the resistors are different.Which resistor has the higher dissipation of power? Explain your answer.

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3) (a) Give the units of resistivity in terms of base units,

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(b) A copper wire has a cross sectional area of 0.62 mm2. If the resistivity of copper is 1.7x10-8 Ωm, find the resistance of copper wire of length 2.0m.

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(c) A wire has a resistance of 12.0 Ω. It is stretched to twice its length. What is the new resistance?

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4) A steady current of 500mA passes through a torch bulb for 12 minutes.

(a) Calculate the charge which flows through the bulb in this time.

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(b) The torch bulb is now connected to a battery of negligible internal resistance. The battery supplies a steady current 0.25A for 30 hours. In this time the energy transferred in the bulb is 120KJ. Calculate

(i) The potential difference across the bulb.

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(ii)Power of the bulb,

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5) A circuit is set up to take some measurements and to plot a graph which shows how the current in 12V 36W electric filament lamp varies with the potential difference across it.(a) Draw a circuit diagram to show all the electric components.

(b) Sketch and label the graph you would expect to obtain.

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(c) Explain the change in resistance as voltage increases.

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6) A copper wire has a cross-sectional area of 0.20x10-6 m2. Copper has 1.0x1029 free electrons per cubic meter.(a)Calculate the current through the wire when the drift speed of the electron is

0.94mms-1.

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(b) The wire is 5.0m long. Copper has a resistivity of 1.7x10-8 Ωm. Calculate the resistance of the wire.

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(c)Calculate the potential difference across the wire.

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(d) A second wire with the same dimensions is made from a material that has a greater resistivity than copper. Explain how, if at all current will differ from that in the copper wire when the same P.d. is applied across it.

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(e) The number of free electrons per cubic meter in this wire is the same as that in the copper wire. Compare the drift velocities of the free electrons in the two wires.

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