� Since i = dq / dt is the instantaneous current in the circuit so
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is the peak value of current Comparing equation ( 13 ) with V = V 0 sinωt , we see that in a perfect capacitor current leads emf by a phase angle of π / 2 This phase relationship is graphically shown below in the figure
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Again comparing peak value of current with ohm ' s law , we find that quantity 1 / ωC has the dimension of the resistance Thus the quantity X C = 1 / ωC = 1 / 2πfC ---( 14 ) is known as capacitive reactance From equation ( 14 ) we see that capacitive reactance decreases with increasing frequency of current and in infinite for direct current for which frequency f = 0
LCR series circuit
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Figure below shows a circuit containing a capacitor , resistor and inductor connected in series through an alternating voltage source