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The capacity of a pure capacitor is 1 farad in a d.c. circuit. Then what will be its capacitive reactance?

Asked in GUJCET 2013 · Behaviour of R, L and C separately

• (1) 1/2 Ω
• (2) Infinite
• (3) 1 Ω
• (4) Zero

Step-by-step solution

Why the other options are wrong

• (1) No single slip gives 1/2 Ω. That reactance would need 1/(ω C)=1/2, i.e. ω=2 rad s⁻¹; for d.c. ω=0 and no finite reactance is possible.
• (3) 1 Ω comes from X_C=1/C with C=1 F, leaving the frequency out. The reactance is 1/(ω C), and for d.c. ω=0.
• (4) Zero reactance is how an inductor behaves in d.c. (X_L=ω L=0). A capacitor does the opposite: it blocks a steady current completely.

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