# Physics Questions and Answers – Capacitors and Capacitance

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Capacitors and Capacitance”.

1. What is the dimensional formula of capacitance of a capacitor?
a) M1L2T-4I-2
b) M-1L-2T4I2
c) M-1L-2T6
d) M-2L2T4

Explanation: We know that Capacitance=Charge*(voltage)-1
Now charge=current*time=[I1T1].
voltage=electric field*distance, and electric field=force*(charge)-1
Since we know the dimensional formula of force is [M1L1T-2], therefore,
Electric field=[M1L1T-2] * [I1T1]-1=[M1L1T-3I-1].
Finally, voltage becomes=[M1L1T-3I-1] *L.
Hence, we conclude that dimensional formula of capacitance is [I1T1] * ([M1L1T-3I-1] *L)-1 that is M-1L-2T4I2.

2. When ‘n’ capacitors are connected in series the total capacitance(C) of the combination is given by ______
a) C=C1+C2+C3+C4+…..+Cn
b) C=C1*C2*C3*C4*…..*Cn
c) $$\frac {1}{C} = \frac {1}{C_1} + \frac {1}{C_2} + \frac {1}{C_3} + ……. + \frac {1}{C_n}$$
d) C=$$\frac {(C_1+C_2+C_3+C_4+……+C_n)}{n}$$

Explanation: The equivalent capacitance of the parallel plate capacitors connected in series is given by the sum of the reciprocals of the individual capacitances. That is mathematically,
$$\frac {1}{C} = \frac {1}{C_1} + \frac {1}{C_2} + \frac {1}{C_3} + ……. + \frac {1}{C_n}$$

3. What is the value of capacitance of a capacitor if it has a charge of 9C and voltage of 5V?
a) 1.8F
b) 45F
c) 4.5F
d) 8.1F

Explanation: Since we know that capacitance=$$\frac {charge}{voltage}$$.
Therefore capacitance=$$\frac {9}{5}$$=1.8F.

4. The total capacitance of capacitors connected in parallel is given by _____
a) product of the individual capacitors in parallel
b) sum of all the individual capacitors in parallel
c) sum of their reciprocals
d) product of their reciprocals

Explanation: The equivalent capacitance of the capacitors connected in parallel is given by sum of their individual capacitances, that is if there are n capacitors in parallel the total capacitance is given by, C=C1+C2+C3+C4+…..+Cn.

5. What is the total charge on the parallel plate capacitor shown? a) 2Q
b) $$\frac {Q}{2}$$
c) 0
d) $$\frac {-Q}{2}$$

Explanation: Since the total charge on a capacitor is given by sum of the charges on the two parallel plates, here charge on each plate is equal and opposite, hence –Q+Q=0. Therefore, the total charge on the capacitor is 0.

6. What happens to the capacitance when a dielectric material is inserted between the plates of a parallel plate capacitor?
a) Capacitance decreases
b) Capacitance remains same
c) Capacitance increases
d) Depends upon the material of the dielectric

Explanation: When a dielectric material is inserted between the plates of the parallel plate capacitor, the capacitance of the capacitor increases with a factor of K. That is C=KC0.

Sanfoundry Global Education & Learning Series – Physics – Class 12. 