Which statement about capacitors in DC circuits is true?

• A. They pass DC currents without impedance.
• B. They behave as short circuits at steady state.
• C. They create a constant current source.
• D. They store energy in an electric field.

Answer: (D)

In DC circuits, a capacitor’s key behavior is to store energy in an electric field between its plates and then block steady current. When you connect a DC source, the capacitor charges up to the supply voltage, and after it’s charged, the current drops to zero. The energy stored is 1/2 C V^2, with V being the voltage across the plates, and that energy remains in the electric field as long as charge is on the plates.

This is why storing energy in an electric field is the true statement: the capacitor’s primary role in DC is energy storage rather than continuous energy delivery. The current through a capacitor is i = C dv/dt, so it flows only while the voltage across the plates is changing. For steady DC, dv/dt is zero, hence no steady current flows.

The other descriptions don’t fit DC behavior. A capacitor does not pass DC currents without impedance; its DC impedance is effectively infinite once charged, so no steady current flows. It does not act as a short circuit at steady state. It also does not provide a constant current source; it only supplies current during transient changes in voltage, not continuously.