4.2.3. Electromotive force and potential difference
A subsection of Physics, 5054, through 4. Electricity and magnetism
Listing 10 of 34 questions
Measurements are made of the current in a metal wire and the potential difference (p.d.) across it. shows a graph of the current against the p.d. for the wire. 0.1 0.2 0.3 0.4 current / A 0.5 p.d. / V State the relationship between the current and the p.d. for the metal wire. State how the graph shows that the temperature of the wire does not change in the experiment. Another wire of the same material has the same length as the original wire but has only half the cross-sectional area. 1. Compare the resistance of the new wire and the original wire. 2. On , draw the graph for the new wire. Three resistors are connected to a d.c. power supply, as shown in . The electromotive force (e.m.f.) of the power supply is 6.0 V. 6.0 V 24 Ω 20 Ω 80 Ω Calculate 1. the total resistance of the circuit, resistance = 2. the current supplied by the power supply, current = 3. the p.d. across the 20 Ω resistor. p.d. = The d.c. power supply is a battery that contains a number of cells. Each cell has an electromotive force (e.m.f.) of 1.5 V. 1. State what is meant by the electromotive force (e.m.f.) of a cell. 2. In the space below, draw a diagram to show how four of these cells are connected to make a battery of e.m.f. 6.0 V. Mark the positive terminal of the battery. 3. In another arrangement to produce a battery of e.m.f. 6.0 V, eight cells of e.m.f. 1.5 V are connected. In this arrangement, some cells are connected in series and some in parallel. In the space below, draw a diagram to show how the eight cells are connected to make the battery. State one advantage of using a battery made from cells in parallel rather than a single cell.
5054_s17_qp_22
THEORY
2017
Paper 2, Variant 2
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shows a wire of length l and cross-sectional area A. l A State how the resistance of the wire in depends on: l A. The cross-sectional area of a piece of metal wire is 7.5 × 10–4 cm2. The resistance of a 1.0 m length of the same wire is 6.4 Ω. The wire is made from metal W. shows a solid cube of side 1.0 cm. It is also made from metal W. 1.0 cm 1.0 cm 1.0 cm A B Calculate the resistance between the two opposite faces A and B of the cube. resistance = The wire in part is taped to a metre rule. shows that a 1.0 m length of the wire (resistance 6.4 Ω) is connected in series with a switch, a cell of electromotive force (e.m.f.) 1.2 V and a resistor of resistance 9.6 Ω. P 0 cm wire 1.2 V 9.6 Ω The switch is closed. Explain what is meant by electromotive force (e.m.f.). Calculate the potential difference (p.d.) across the 1.0 m length of the wire. p.d. = One input terminal of an oscilloscope is connected to the wire at point P, the 0 cm mark of the metre rule. The other terminal of the oscilloscope is connected to a sliding contact. Initially, this contact touches the wire at point P. The Y-gain setting on the oscilloscope is 0.20 V / cm. shows the screen of the oscilloscope with a horizontal trace across the middle of the screen. 1.0 cm 1.0 cm trace The sliding contact is slowly moved along the wire until it reaches the other end of the metre rule. Describe and explain what happens to the trace on the screen. A second, identical 1.2 V cell is connected in parallel with the cell in the circuit in . State one advantage of using two cells in parallel rather than a single cell. State and explain the effect on the trace in of adding the second cell in parallel.
5054_w20_qp_21
THEORY
2020
Paper 2, Variant 1
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The power supply in a circuit is made from several cells, each with the same electromotive force (e.m.f.). The cells are connected in parallel. Explain what is meant by ‘electromotive force’. State one advantage of using several cells in parallel rather than a single cell as the power supply. The power supply is connected in series to a resistor of resistance 4000 Ω and a thermistor. There is a voltmeter in parallel with the resistor. is the circuit diagram. V 4000 Ω power supply thermistor The temperature of the thermistor increases. Explain what happens to the reading on the voltmeter. The e.m.f. of the power supply is 1.5 V. Calculate the reading on the voltmeter when the resistance of the thermistor is 8000 Ω. reading =
5054_w22_qp_22
THEORY
2022
Paper 2, Variant 2
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Questions Discovered
34