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19.1. Capacitors and capacitance
A subsection of Physics, 9702, through 19. Capacitance
Listing 10 of 23 questions
State two uses of capacitors in electrical circuits, other than for the smoothing of direct current. 1. 2. The combined capacitance between terminals A and B of the arrangement shown in is 4.0 μF. A B & & +F +F Two capacitors each have capacitance C and the remaining capacitors each have capacitance 3.0 μF. The potential difference (p.d.) between terminals A and B is 12 V. Determine the capacitance C. C = μF Calculate the magnitude of the total positive charge transferred to the arrangement. charge = μC Use your answer in to state the magnitude of the charge on one plate of 1. a capacitor of capacitance C, charge = μC 2. a capacitor of capacitance 3.0 μF. charge = μC
9702_s16_qp_42
THEORY
2016
Paper 4, Variant 2
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Explain what is meant by the capacitance of a parallel plate capacitor. Three parallel plate capacitors each have a capacitance of 6.0 μF. Draw circuit diagrams, one in each case, to show how the capacitors may be connected together to give a combined capacitance of 9.0 μF, 4.0 μF. Two capacitors of capacitances 3.0 μF and 2.0 μF are connected in series with a battery of electromotive force (e.m.f.) 8.0 V, as shown in . 3.0 μF 2.0 μF 8.0 V Calculate the combined capacitance of the capacitors. capacitance = μF Use your answer in to determine, for the capacitor of capacitance 3.0 μF, 1. the charge on one plate of the capacitor, charge = μC 2. the energy stored in the capacitor. energy = J
9702_s18_qp_42
THEORY
2018
Paper 4, Variant 2
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State two different functions of capacitors in electrical circuits. 1. 2. Three uncharged capacitors of capacitances C1, C2 and C3 are connected in series with a battery of electromotive force (e.m.f.) E and a switch, as shown in . E C1 plate P charge +q C2 C3 When the switch is closed, there is a charge + q on plate P of the capacitor of capacitance C1. Show that the combined capacitance C of the three capacitors is given by the expression 1 . C C C C = + + A student has available four capacitors, each of capacitance 20 μF. Draw circuit diagrams, one in each case, to show how the student may connect some or all of the capacitors to produce a combined capacitance of: 60 μF 15 μF.
9702_s19_qp_41
THEORY
2019
Paper 4, Variant 1
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State two different functions of capacitors in electrical circuits. 1. 2. Three uncharged capacitors of capacitances C1, C2 and C3 are connected in series with a battery of electromotive force (e.m.f.) E and a switch, as shown in . E C1 plate P charge +q C2 C3 When the switch is closed, there is a charge + q on plate P of the capacitor of capacitance C1. Show that the combined capacitance C of the three capacitors is given by the expression 1 . C C C C = + + A student has available four capacitors, each of capacitance 20 μF. Draw circuit diagrams, one in each case, to show how the student may connect some or all of the capacitors to produce a combined capacitance of: 60 μF 15 μF.
9702_s19_qp_43
THEORY
2019
Paper 4, Variant 3
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Define capacitance. An isolated metal sphere of radius R has a charge +Q on it. The charge may be considered to act as a point charge at the centre of the sphere. Show that the capacitance C of the sphere is given by the expression C = 40R where 0 is the permittivity of free space. In order to investigate electrical discharges in a laboratory, an isolated metal sphere of radius 63 cm is charged to a potential of 1.2 × 106 V. At this potential, there is an electrical discharge in which the sphere loses 75% of its energy. Calculate the capacitance of the sphere, stating the unit in which it is measured, capacitance = the potential of the sphere after the discharge has taken place. potential = V
9702_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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Define capacitance. A capacitor is made of two metal plates, insulated from one another, as shown in . metal plate insulation Explain why the capacitor is said to store energy but not charge. Three uncharged capacitors X, Y and Z, each of capacitance 12 μF, are connected as shown in . 12 ȝF 12 ȝF Z Y 12 ȝF X A B A potential difference of 9.0 V is applied between points A and B. Calculate the combined capacitance of the capacitors X, Y and Z. capacitance = μF Explain why, when the potential difference of 9.0 V is applied, the charge on one plate of capacitor X is 72 μC. Determine 1. the potential difference across capacitor X, potential difference = V 2. the charge on one plate of capacitor Y. charge = μC
9702_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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Define capacitance. A capacitor is made of two metal plates, insulated from one another, as shown in . metal plate insulation Explain why the capacitor is said to store energy but not charge. Three uncharged capacitors X, Y and Z, each of capacitance 12 μF, are connected as shown in . 12 ȝF 12 ȝF Z Y 12 ȝF X A B A potential difference of 9.0 V is applied between points A and B. Calculate the combined capacitance of the capacitors X, Y and Z. capacitance = μF Explain why, when the potential difference of 9.0 V is applied, the charge on one plate of capacitor X is 72 μC. Determine 1. the potential difference across capacitor X, potential difference = V 2. the charge on one plate of capacitor Y. charge = μC
9702_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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State two functions of capacitors connected in electrical circuits. 1. 2. Three capacitors are connected in parallel to a power supply as shown in . V C1 C3 C2 The capacitors have capacitances C1, C2 and C3. The power supply provides a potential difference V. Explain why the charge on the positive plate of each capacitor is different. Use your answer in to show that the combined capacitance C of the three capacitors is given by the expression C = C1 + C2 + C3. A student has available three capacitors, each of capacitance 12 μF. Draw circuit diagrams, one in each case, to show how the student connects the three capacitors to provide a combined capacitance of 8 μF, 18 μF.
9702_w13_qp_43
THEORY
2013
Paper 4, Variant 3
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Define capacitance. Use the expression for the electric potential due to a point charge to show that an isolated metal sphere of diameter 25 cm has a capacitance of 1.4 × 10–11 F. Three capacitors of capacitances 2.0 μF, 3.0 μF and 4.0 μF are connected as shown in to a battery of e.m.f. 9.0 V. 4.0 μF 2.0 μF 3.0 μF 9.0 V Determine the combined capacitance of the three capacitors, capacitance = μF the potential difference across the capacitor of capacitance 3.0 μF, potential difference = V the positive charge stored on the capacitor of capacitance 2.0 μF. charge = μC
9702_w16_qp_42
THEORY
2016
Paper 4, Variant 2
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Questions Discovered
23