Capacitor And Capacitance MCQ - Practice Questions & Answers

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Capacitor is considered one of the most asked concept.
16 Questions around this concept.

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A light bulb, a capacitor, and a battery are connected together as shown here, with switch S initially open. When the switch S is closed, which one of the following is true

The bulb will light up for an instant when the capacitor starts charging

The bulb will light up when the capacitor is fully charged

The bulb will not light up at all

The bulb will light up and go off at regular intervals

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A 400 $\mu C$ capacitor is charged at a steady rate of 100 $\mu C$ /sec. The potential difference across the capacitor will be 10 V after an interval of

5 sec

20 sec

25 sec

40 sec

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Concepts Covered - 1

Capacitor

A capacitor is a passive two-terminal electrical component used to store energy electrostatically in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). The conductors can be thin films of metal, aluminum foil or disks, etc. The 'nonconducting' dielectric acts to increase the capacitor's charge capacity. A dielectric can be glass, ceramic, plastic film, air, paper, mica, etc. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.

Capacitance: Capacitance is the ability of a capacitor to hold an electrical charge. Capacitors are components in an electrical circuit that can store a charge and are considered one of the three fundamental electronic components along with inductors and resistors.

For an isolated capacitor, capacitance is defined as the ratio of the charge to the potential of a capacitor.

$C=\frac{Q}{V}$

As Q increases V also increases because potential depends on the charge.

$Q\propto V \\ \ \ \ \ \ Q=CV$

Therefore Capacitance is a constant quantity.

Unit of Capacitance-

$S.I unit\; -\; \frac{C}{V}=\; farad\left ( f \right )$

Smaller S.I unit is $mf\; ,\; \mu f\: ,\: nf\: and\: Pf$

$C.G.S\: -\: Stat\: farad \ \ and \ \ \ 1F=9\times 10^{11}stat farad$

$\dpi{100} Dimension = M^{-1}L^{-2}T^{4}A^{2}$

If V=1V, C=Q. Hence, we define the capacitance of an conductor as the charge required to rise the potential of the conductor by 1V. In the SI system, the unit of capacitance is farad.

CAPACITANCE OF A SPHERICAL CONDUCTOR OR CAPACITOR:

A single conductor can also act as a capacitor. For this, let a charge q be given to a spherical conductor of radius R, then potential on it is

$V=\frac{1}{4 \pi \varepsilon_{0}} \frac{q}{R}$
The other conductor is supposed to be at infinity, whose potential will be taken as zero. So the potential difference between the sphere and the conductor at infinity becomes V-0=V.

$C=\frac{q}{V}=4 \pi \varepsilon_{0} R$