Test on Resistor, inductor and capacitor in an AC circuit

Question 1: In an AC circuit, a resistor dissipates electrical energy as heat.

A. Yes

B. No

Explanation: Resistors dissipate electrical energy as heat, and the average power dissipated is given by P = I_RMS² · R or P = V_RMS² / R.

Question 2: In a purely capacitive AC circuit, what is the phase relationship between the current through the capacitor and the voltage across it?

A. The current lags the voltage by 90 degrees.

B. The current leads the voltage by 90 degrees.

C. The current is in phase with the voltage.

D. The voltage leads the current by 90 degrees.

Explanation: According to the study materials, in a purely capacitive AC circuit, the current through the capacitor leads the voltage across it by a phase angle of 90 degrees (π/2 radians). This means the current reaches its peak value a quarter of a cycle before the voltage reaches its peak value.

Question 3: The peak current through a resistor in an AC circuit changes as the frequency of the AC voltage source is adjusted, even if the peak voltage and resistance remain constant.

A. Yes

B. No

Explanation: The study materials state that for a resistor, as the frequency changes, the peak current remains constant for a given peak voltage and resistance. This contradicts the idea that the peak current would change with frequency for a resistor.

Question 4: Ideal resistance results in zero average power dissipation in AC circuits.

A. Yes

B. No

Explanation: Resistance dissipates energy as heat, converting electrical energy into heat. Ideal reactance (inductive or capacitive), however, stores and returns energy, resulting in zero average power dissipation in ideal components.

Question 5: Which of the following statements correctly describe the phase relationship between voltage and current in ideal passive electrical components, according to the provided study materials?

A. In an ideal inductor, the current leads the voltage.

B. In an ideal capacitor, the current leads the voltage.

C. In an ideal resistor, the voltage and current are always perfectly aligned, meaning they are in phase.

D. In an ideal capacitor, the voltage leads the current by 90 degrees.

Explanation: According to the study materials, the mnemonic 'ELI the ICE man' helps to remember phase relationships. 'ELI' means that in an inductor (L), voltage (E) leads current (I). 'ICE' means that in a capacitor (C), current (I) leads voltage (E). Therefore, the statement 'In an ideal capacitor, the current leads the voltage' is correct. The material also states that for a resistor, 'the voltage and current waveforms will always be perfectly aligned', meaning they are in phase, making that statement correct as well. The statement 'In an ideal inductor, the current leads the voltage' is incorrect because voltage leads current in an inductor. The statement 'In an ideal capacitor, the voltage leads the current by 90 degrees' is incorrect because current leads voltage in a capacitor.