ECEN test 2 questions with verified
answers graded A+
How can current flow "through" a capacitor even though a nonconducting layer separates the
metallic parts? - correct answer ✔✔ As charges flow in and accumulate on one plate, an equal
amount of charge flows out of the other plate. Thus, current seems to flow through a capacitor.
What current flows through an ideal capacitor if the voltage across the capacitor is constant
with time? - correct answer ✔✔ zero
To what circuit element is an ideal capacitor equivalent in circuits for which the currents and
voltages are constant with time? - correct answer ✔✔ open circuit
if the power is positive, - correct answer ✔✔ the energy is absorbed by the capacitor
if the power is negative - correct answer ✔✔ the energy is delivered by the capacitor
what resistances correspond to a short and an open circuit for a resistor. - correct answer ✔✔
By definition, the voltage across a short circuit must be zero. Since we have v=Ri for a resistor,
zero resistance corresponds to a short circuit. For an open circuit, the current must be zero. This
requires infinite resistance.
what capacitances correspond to a short and an uncharged capacitor. - correct answer ✔✔ For
an initially uncharged capacitance, we have
V= (1/C)∫i(t) dt and I = C (dv/dt)
For the voltage to be zero for all values of current and time, the capacitance must be infinite.
Thus, an infinite initially uncharged capacitance is equivalent to a short circuit, and a
capacitance of zero is equivalent to an open circuit.
answers graded A+
How can current flow "through" a capacitor even though a nonconducting layer separates the
metallic parts? - correct answer ✔✔ As charges flow in and accumulate on one plate, an equal
amount of charge flows out of the other plate. Thus, current seems to flow through a capacitor.
What current flows through an ideal capacitor if the voltage across the capacitor is constant
with time? - correct answer ✔✔ zero
To what circuit element is an ideal capacitor equivalent in circuits for which the currents and
voltages are constant with time? - correct answer ✔✔ open circuit
if the power is positive, - correct answer ✔✔ the energy is absorbed by the capacitor
if the power is negative - correct answer ✔✔ the energy is delivered by the capacitor
what resistances correspond to a short and an open circuit for a resistor. - correct answer ✔✔
By definition, the voltage across a short circuit must be zero. Since we have v=Ri for a resistor,
zero resistance corresponds to a short circuit. For an open circuit, the current must be zero. This
requires infinite resistance.
what capacitances correspond to a short and an uncharged capacitor. - correct answer ✔✔ For
an initially uncharged capacitance, we have
V= (1/C)∫i(t) dt and I = C (dv/dt)
For the voltage to be zero for all values of current and time, the capacitance must be infinite.
Thus, an infinite initially uncharged capacitance is equivalent to a short circuit, and a
capacitance of zero is equivalent to an open circuit.
