10 question-answer on capacitors | Learn Physics

10 question-answer on capacitors

1.       A parallel plate air capacitor has a capacitance 10µF. If the distance between the plates is trebled and a dielectric medium is introduced, the capacitance becomes 72µF. the dielectric constant of the medium is:

(a)    4

(b)   9

(c)    12

(d)   2

Ans: (c)

2.       Three capacitors of capacitances 4µF, 6µF and 12µF are connected first in series and then in parallel. What is the ratio of equivalent capacitance in the two cases:

(a)    2 : 3

(b)   1 : 11

(c)    11 : 1

(d)   1 : 3

Ans: ( b)

3.       The plates of a parallel plate capacitor are charged up to 100 volt. A 2  mm thick slab is inserted between the plates, then to maintain the same potential diff., the distance between the capacitor plates is increased by 1.6 mm. the dielectric constant of the slab is:

(a)    5

(b)   1.25

(c)    3

(d)   2.5

Ans: ( a)

4.       When a capacitor is connected to a battery

(a)    An alternating current flows in the circuit

(b)   No current flows at all

(c)    A current flows for some time and finally it decreases to zero

(d)   Current keeps on increasing and reaches maximum after some time.

Ans: ( c)

5.       The energy of a charged capacitor resides in

(a)    The electric field only

(b)   The magnetic field only

(c)    Both the electric and magnetic field

(d)   Neither in the electric nor in the magnetic field

Ans: ( c)

6.       Three capacitors each of capacitance 1 µF are connected in parallel. To this combination, a forth capacitor of capacitance 1µ F is connected in series. The resultant capacitance of the system is:

(a)    4µF

(b)   4/3 µF

(c)    2µF

(d)   3/4µF

Ans: (d)

7.       When a metal plate is introduced between the two plates of a charged capacitor and insulated from them, then

(a)    The metal plate divides the capacitor in to two capacitors connected in parallel to each other

(b)   The metal plate divides the capacitor in to two capacitors connected in series to each other

(c)    The metal plate is equivalent to a dielectric of zero dielectric constant

(d)   The metal plate is equivalent to a dielectric of infinite dielectric constant

Ans: (b,d)

8.       The potential gradient at which dielectric of the condenser just gets punctured, is called

(a)    Dielectric constant

(b)   Dielectric strength

(c)    Dielectric resistance

(d)   Dielectric number

Ans: (b)

9.       If a dielectric is introduced between the elements of condenser, kept at a constant potential difference, then the charge on condenser

(a)    Increases

(b)   Decreases

(c)    Remains constant

(d)   Either ‘b’ or ‘c’

Ans: ( a)

10.   A capacitor works in

(a)    A.C. circuits

(b)   D.C. circuits

(c)    Both ‘a’ and ‘b’

(d)   Neither ‘a’ nor ‘b’

Ans: (a)