Question

The capacitor offers zero resistance to
A). D.C. only
B). A.C. & D.C.
C). A.C. only
D). Neither A.C. nor D.C.

Answer 1

Hint: There are two types of reactance: the capacitive reactance (XC) and the inductance reactance (XL). The total reactance (X) is the difference between the capacitive reactance (XC) and the inductance reactance (XL).
The expression for the total reactance is:
The total reactance (X) = the inductance reactance (XL) - the capacitive reactance (XC).

Complete step by step solution:
The inductance reactance is given as
${X_L} = {{\omega L}}$
Here XL is the inductive reactance
$\omega $ Is the angular frequency
L is the inductance
The capacitance reactance is given as
\[{X_C} = \dfrac{1}{{\omega C}}\]
Here XC is the capacitance reactance
$\omega $ Is the angular frequency
C is the capacitance
The capacitive reactance is a function of frequency, when it is in D.C., no frequency is there and resistance is infinite.
For AC, the reactance is calculated by the above the expression.
From this relation we can see the value of capacitive reactance & thus, its overall impedance decreases to zero as the frequency increases acting like a short-circuit.
Likewise, as the frequency approaches zero or D.C., the capacitors reactance increases to infinity, acting like an open circuit.
So, the option (D) is correct.

Note: When a capacitor is connected to DC supply, its frequency being zero and hence the reactance becomes infinite so it will block DC. A capacitor has a very high resistance for DC.
Capacitors act such as a battery, but it charges very rapidly and discharges too far from the battery which takes a considerable amount of time.
In initial condition, the capacitor conducts when it is connected to DC supply, but at once it gets fully charged, then further, it’s not going to conduct.