27 past paper MCQs on Charging and Discharging of a Capacitor, from the Electrostatics unit of MDCAT Physics. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.
1.By increasing the area of the plates and decreasing the distance between them, the capacitance of a capacitor: (MDCAT 2020)
Correct answer: (a) increases
$C=\varepsilon_0A/d$ rises with the area and falls with the separation.
2.A capacitor is charged with a battery and the energy stored is $U$. After disconnecting the battery, another capacitor of the same capacity is connected in parallel to the first one. The energy stored in each capacitor is: (MDCAT 2022)
Correct answer: (b) $U/4$
The charge is shared equally, and $E=Q^2/2C$ with half the charge is a quarter of the energy.
3.A capacitor of capacitance $C$ has a charge $Q$ and stored energy $W$. If the charge is increased to $2Q$, the stored energy will be: (MDCAT 2022)
Correct answer: (b) $4W$
$E=Q^2/2C$ goes as the square of the charge.
4.The SI unit of the capacitance of a capacitor is the: (MDCAT 2024)
Correct answer: (c) farad
One farad is one coulomb per volt.
5.The energy stored in a capacitor is: (NUMS MDCAT 2025)
Correct answer: (b) QV/2
The charge builds up as the voltage rises, so the stored energy is $\tfrac12QV$, not $QV$.
6.The unit of RC in case of charging a capacitor is: (SZABMU MDCAT 2025)
Correct answer: (b) Seconds
Ohms times farads give seconds, which is why $RC$ is called the time constant.
7.The S.I unit of capacitance of a capacitor is: (UHS MDCAT 2024)
Correct answer: (c) Farad
Capacitance is measured in farads, one farad being a coulomb per volt.
8.In the case of a parallel plate capacitor, when the distance between the two plates is reduced to half and the area of the plate doubled, the capacitance (KMU MDCAT 2024)
Correct answer: (a) Increases four times
$C=\varepsilon A/d$ gains two from the area and two from the halved separation.
9.If the dielectric material between the plates of the capacitor is removed, what happens to the electric field between the plates? (KMU MDCAT 2024)
Correct answer: (c) The electric field increases
The dielectric was weakening the field; with the charge unchanged, taking it out lets the field rise.
10.Capacitance of a capacitor increases with a decrease in: (KMU MDCAT 2024)
Correct answer: (d) Plate separation
$C=\varepsilon A/d$, so the closer the plates the greater the capacitance.
11.A capacitor can be fully charged because time required is: (NUMS MDCAT 2024)
Correct answer: (d) Infinity
The charge approaches its final value asymptotically, so strictly it is never quite reached.
12.If electric field intensity between capacitor plates doubles, energy stored becomes: (NUMS MDCAT 2024)
Correct answer: (d) Quadruple
The energy density goes as the square of the field, so doubling the field gives four times the energy.
13.A capacitor of capacitance 'C' has a charge 'Q' and stored energy is 'w'. If the charge is increases to '2Q'. The stored energy will be: (UHS MDCAT 2023)
Correct answer: (b) 4W
$U=Q^2/2C$ goes as the square of the charge, so twice the charge stores four times the energy.
14.The capacitance of capacitor does not depend on: (SZABMU MDCAT 2023)
Correct answer: (d) Thickness of plates
$C=\varepsilon A/d$ carries the area, the separation and the medium, but not how thick the plates are.
15.While studying charging and discharging of a capacitor, Rc = Resistance × Capacitance is known as: (NUMS MDCAT 2023)
Correct answer: (b) Time constant
$RC$ has the dimension of time and is called the time constant of the circuit.
16.In parallel combination of two capacitors, their equivalent capacitance is equal to: (NUMS MDCAT 2023)
Correct answer: (a) C1 + C2
Capacitors in parallel share the same voltage, so their capacitances add.
17.To store the electric charge the ultra-capacitors use _______ effect. (UHS MDCAT 2023)
Correct answer: (b) Double layer
An ultracapacitor stores charge in the electrical double layer at the electrode surface.
18.The device used to store a charge is called: (PMC MDCAT 2022)
Correct answer: (b) Capacitor
A capacitor stores charge, and with it energy.
19.In the combination of capacitors in series, the capacitors are connected: (PMC MDCAT 2022)
Correct answer: (b) side by side
Capacitors in series are joined end to end, so the same charge passes through all of them.
20.In parallel plate capacitor Capacitance depends on: (PMC MDCAT 2022)
Correct answer: (d) Cross-sectional area
$C=\varepsilon A/d$ carries the area and the separation, not the charge or the voltage.
21.Parallel combination of two capacitor C1 and C2 Is: (PMC MDCAT 2022)
Correct answer: (a) C1+ C2
Capacitors in parallel share the same voltage, so their capacitances add.
22.Energy stored in a capacitor is given by: (NUMS MDCAT 2022)
Correct answer: (a) E = ½ cv^2
The stored energy is $\tfrac12CV^2$.
23.Q.64 It stores electrical potential energy: (NUMS MDCAT 2022)
Correct answer: (a) Capacitor
A capacitor stores charge and with it electrical potential energy.
24.Consider two capacitors with capacitance 2µF and 4µF. With which type of connection will the 4µF capacitor have a greater amount of stored energy than the 2µF capacitor? (PMC Practice 2021)
Correct answer: (b) Parallel
In parallel both hold the same voltage, and $\tfrac12CV^2$ is larger for the larger capacitance.
25.Ohm multiplied by farad is equivalent to: (PMC MDCAT 2020)
Correct answer: (a) Time
Ohms times farads give seconds, which is why $RC$ is a time constant.
26.In what form is the energy stored in a charged capacitor? (PMC MDCAT 2020)
Correct answer: (b) electrical potential
The work done in charging it is stored as electrical potential energy in the field between the plates.
27.If the length, width and separation between the plates of a parallel plate capacitor is doubled then its capacitance becomes: (UHS MDCAT 2016)
Correct answer: (a) Double
$C=\varepsilon A/d$: four times the area over twice the separation is twice the capacitance.