[Unit 10.05] Potential Difference and...
Transcript of [Unit 10.05] Potential Difference and...
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Current ElectricityCurrent Current ElectricityElectricity
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Prepared in Dec 1998Second editing in March 2000
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At the end of this unit you should be able to :
1. show understanding that potential difference across a circuit component is measured in volt.
2. use the concept of e.m.f. is measured by energy dissipated by a source in driving a charge round a complete circuit.
3. show appreciation that volt is given by J/C.4. use the equation V = E/Q.5. use and describe the use of a voltmeter with
different ranges.
Learning objectivesLearning objectives
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Potential DifferencePotential DifferencePotential Difference• Potential difference also called as voltage or as
p.d.• The voltage (p.d.) across the bulb is the amount
of energy by each coulomb of charge.• Thus
• The term potential difference is used for the voltage between two points in a circuit.
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V = p.d. E = energy Q = Charge
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Potential DifferencePotential DifferencePotential Difference• The voltage (p.d.) across the bulb is the
amount of energy by each coulomb of charge.
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Electromotive ForceElectromotive Forcee.m.f.e.m.f.
• A cell (or a battery) pushes electrons round a circuit. It is a kind of electron pump.
• Different cells can exert different electrical pressures.
• For a higher electrical pressure, the electrons will flow out at a faster rate, i.e. a large current.
• This electrical pressure is called electromotive force ( e.m.f.).
• The SI Unit of e.m.f. is volt, V.
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Electromotive ForceElectromotive Forcee.m.f.e.m.f.
• Hence,
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e.m.f. = Energy supplied by the cellcharges flow through the cell
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ExampleExampleExample
• When 20 C of charge flows through a potential difference of 12 V, how much energy is involved ?
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– since E = VQ– = 12 x 20– = 240 J
– 240 J of energy is involved.
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VoltmeterVoltmeterVoltmeter• Voltmeter is used to measure the amount
of voltage across two points in a circuit.• It is always connected in parallel in the
circuit.• Its internal resistance has very high value.
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GCE OGCE O--LevelLevelPast Examination PaperPast Examination Paper
Science (Physics)
All rights go to University of Cambridge Examinations Syndicate and other sources
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Nov 1995O’ level Physics
15. How could the unit of potential difference, the volt, also be written?
A A/sB C/AC C/JD J/C
DHint:
V = E/Q
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GCE O Nov 1997
15. 50 J of energy are dissipated for every 10 C ofcharge passing through a resistance.Which instrument wold allow this to be measured ?
A an ammeter in series with the resistorB an ammeter in parallel with the resistorC a voltmeter in series with the resistorD a voltmeter in parallel with the resistor
DHint:V = E / Q
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November 1992
7. The diagram shows acircuit containing two identical lamps and a resistor. Each lamp is marked 1.5 V 0.4 A. This refers to theconditions when the lamps are a normal brightness. The lamps can be operated at the normal brightness by using a 6 V supply and a resistor., R.(a) What is the potential difference between Y and
Z? ______________________________ [1]1.5 V
hint