© examsnet.com
Question : 35
Total: 35
A capacitor is a system of two conductors separated by an insulator. The two conductors have equal and opposite charges with a potential difference between them. The capacitance of a capacitor depends on the geometrical configuration (shape, size and separation) of the system and also on the nature of the insulator separating the two conductors. They are used to store charges. Like resistors, capacitors can be arranged in series or parallel or a combination of both to obtain desired value of capacitance.
(i) Find the equivalent capacitance between pointsA B
(ii) A dielectric slab is inserted between the plates of a parallel plate capacitor. The electric field between the plates decreases. Explain.
(iii) A capacitor A of capacitanceC Q B
OR
(iii) Two slabs of dielectric constants2 K K A d
(i) Find the equivalent capacitance between points
(ii) A dielectric slab is inserted between the plates of a parallel plate capacitor. The electric field between the plates decreases. Explain.
(iii) A capacitor A of capacitance
OR
(iii) Two slabs of dielectric constants
Solution: 👈: Video Solution
Ans. (i) The given combination:
Initially the capacitor between A and B is not considered.
So, the circuit may be redrawn as
E F
The capacitance betweenA B C
Now capacitor between A and B (left out initially) is considered.mathrm A B 2 C
(ii) When a dielectric is placed between charged plates of a capacitor, the polarization of dielectric produces an electric field opposing the field produced by the charges on the plate. Thus, the resultant electric field between the plates decreases.
(iii) Both capacitors will attain a common potential,V C
(a)V C =
=
=
(b) Final charge on capacitorA
= Q A = C V C
=
=
So, charge lost by capacitorA
= Q −
=
OR
By placing the dielectric slab, it behaves like two capacitors in series
C 1 =
=
C 2 =
=
=
+
Or,
=
+
Or,
=
∴C eq =
Initially the capacitor between A and B is not considered.
So, the circuit may be redrawn as
This is like a balanced Wheatstone bridge. So, the capacitor between
The capacitance between
Now capacitor between A and B (left out initially) is considered.
So, the equivalent capacitance between
(ii) When a dielectric is placed between charged plates of a capacitor, the polarization of dielectric produces an electric field opposing the field produced by the charges on the plate. Thus, the resultant electric field between the plates decreases.
(iii) Both capacitors will attain a common potential,
(a)
(b) Final charge on capacitor
So, charge lost by capacitor
OR
By placing the dielectric slab, it behaves like two capacitors in series
Or,
Or,
∴
© examsnet.com
Go to Question: