A capacitor in a circuit is initially uncharged. The switch is closed at time format('truetype')%3Bfont-weight%3Anormal%3Bfont-style%3Anormal%3B%7D%3C%2Fstyle%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22Times%20New%20Roman%22%20font-size%3D%2218%22%20font-style%3D%22italic%22%20text-anchor%3D%22middle%22%20x%3D%222.5%22%20y%3D%2216%22%3Et%3C%2Ftext%3E%3Ctext%20font-family%3D%22math17f39f8317fbdb1988ef4c628eb%22%20font-size%3D%2216%22%20text-anchor%3D%22middle%22%20x%3D%2218.5%22%20y%3D%2216%22%3E%3D%3C%2Ftext%3E%3Ctext%20font-family%3D%22Times%20New%20Roman%22%20font-size%3D%2218%22%20text-anchor%3D%22middle%22%20x%3D%2235.5%22%20y%3D%2216%22%3E0%3C%2Ftext%3E%3C%2Fsvg%3E){kind=small}
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Which of the following graphs shows how the potential difference 
across the capacitor, the charge 
on the capacitor, and the current 
in the circuit change with time 
?
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A capacitor of capacitance C discharges through a resistor of resistance R.
Which one of the following statements is true?
the time constant will decrease if C increases
the time constant will increase if R increases
the time constant will increase if R decreases
the time constant will increase if C decreases
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A capacitor in a circuit is initially fully charged. The switch is opened at time .
Which of the following graphs shows how the potential difference across the capacitor, the charge on the capacitor, and the current in the circuit change with time ?
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What is the capacitance of a capacitor in a circuit with a time constant of 90 s when it is discharged through a 300 kΩ resistor?
3.3 kF
0.3 mF
3.3 F
0.3 F
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What is the final current in a circuit after a capacitor of 450 mF is discharged through a 200 Ω resistor in 1 minute? The initial current is 0.7 A.
0.14 A
0.69 A
0.36 A
0.57 A
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A 650 µF capacitor is charge to a pd of 25 V. It is then discharged through a 120 kΩ resistor.
What is the time taken for the pd to fall to 20 V?
5 s
45 s
30 s
17 s
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The graph shows how the charge on a capacitor varies with time as it is discharged through a resistor.
What is the time constant for the circuit?
5.50 s
12.5 s
20.0 s
4.70 s
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A capacitor of capacitance 20 μF is fully charged and the potential difference across its plates is 4.0 V. It is then connected into the circuit as shown.
The switch S is closed at time t = 0 s. Which one of the following statements is incorrect?
The time constant of the circuit is 12 s
After a time equal to the time constant, the charge on the capacitor is 29 µC
After a time equal to twice the time constant, the charge remaining on the capacitor is 
where 
is the charge at time t = 0
The initial charge on the capacitor is 80 µC
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A 1600 µF capacitor C, initially uncharged, is then charged by a battery with an emf of 40 V.
What potential difference does the resistor reach after 3 minutes?
34.8 V
0.094 V
35 V
5.2 V
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When a capacitor discharges through a resistor, the current is 50 % lower in 12 s.
What is the time constant of the capacitor–resistor circuit?
17 s
6.0 s
3.0 s
10 s
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A voltage sensor and a datalogger are used to record the discharge of a 120 mF capacitor in series with a 834 Ω resistor from an initial pd of 7.5 V. The datalogger is capable of recording 1000 readings in 20 s.
Which line, A to D, in the table gives the pd and the number of readings made after a time equal to the time constant of the discharge circuit?
| potential difference / V | number of readings |
A B C D | 2.8 6.1 2.8 6.1 | 5000 5000 200 200 |
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A capacitor of capacitance 500 µF is attached to a potential difference of 15 V and a resistor R. It charges to a potential difference of 12 V in 0.7 s.
What is the resistance of R?
700 Ω
630 Ω
520 Ω
870 Ω
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A capacitor is charged through a 1000 kΩ resistor as shown in the graph below
What is the potential difference across the capacitor after a time equal to one time constant?
73 V
46 V
35 V
12 V
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Switch S in the circuit is held in position 1, so that the capacitor C becomes fully charged to a pd V and stores energy E.
The switch is then moved quickly to position 2, allowing C to discharge through the fixed resistor R. It takes 53 ms for the pd across C to fall to 
.
What period of time must elapse, after the switch has moved to position 2, before the energy stored by C has fallen to 
?
159 ms
106 ms
190 ms
128 ms
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An uncharged 7.4 nF capacitor is connected to a power supply and becomes fully charged. The potential difference across the capacitor is equal to 1.5 V after 0.3 s and it has a time constant of 0.8 s.
How many electrons are transferred to the negative plate of the capacitor at the end of the charging process?
3.3 × 1011
1.1 × 1011
2.2 × 1011
6.6 × 1011
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