Alternating Current

Class 12 · Physics · 16 Questions

Example 7.1beginner🔧 Apply3 marksNumerical

A light bulb is rated at 100W for a 220 V supply. Find (a) the resistance of the bulb; (b) the peak voltage of the source; and (c) the rms current through the bulb.

Example 7.2beginner🔧 Apply2 marksNumerical

A pure inductor of 25.0 mH is connected to a source of 220 V. Find the inductive reactance and rms current in the circuit if the frequency of the source is 50 Hz.

Example 7.3intermediate🔍 Analyze2 marksShort Answer

A lamp is connected in series with a capacitor. Predict your observations for dc and ac connections. What happens in each case if the capacitance of the capacitor is reduced?

Example 7.4intermediate🔧 Apply3 marksNumerical

A 15.0 $\mu$ F capacitor is connected to a 220 V, 50 Hz source. Find the capacitive reactance and the current (rms and peak) in the circuit. If the frequency is doubled, what happens to the capacitive reactance and the current?

Example 7.6intermediate🔧 Apply3 marksNumerical

A resistor of 200 $\Omega$ and a capacitor of 15.0 $\mu$ F are connected in series to a 220 V, 50 Hz ac source. (a) Calculate the current in the circuit; (b) Calculate the voltage (rms) across the resistor and the capacitor. Is the algebraic sum of these voltages more than the source voltage? If yes, resolve the paradox.

Example 7.7intermediate💡 Understand3 marksLong Answer

(a) For circuits used for transporting electric power, a low power factor implies large power loss in transmission. Explain. (b) Power factor can often be improved by the use of a capacitor of appropriate capacitance in the circuit. Explain.

Example 7.8advanced🔧 Apply5 marksNumerical

A sinusoidal voltage of peak value 283 V and frequency 50 Hz is applied to a series $LCR$ circuit in which $R = 3 \Omega$ , $L = 25.48 \text{ mH}$ , and $C = 796 \mu\text{F}$ . Find (a) the impedance of the circuit; (b) the phase difference between the voltage across the source and the current; (c) the power dissipated in the circuit; and (d) the power factor.

Example 7.9intermediate🔧 Apply3 marksNumerical

Suppose the frequency of the source in the previous example can be varied. (a) What is the frequency of the source at which resonance occurs? (b) Calculate the impedance, the current, and the power dissipated at the resonant condition.

Example 7.10beginner💡 Understand2 marksShort Answer

At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. If she/he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work?

7.1beginner🔧 Apply2 marksNumerical

A 100 $\Omega$ resistor is connected to a 220 V, 50 Hz ac supply. (a) What is the rms value of current in the circuit? (b) What is the net power consumed over a full cycle?

7.2beginner🔧 Apply2 marksNumerical

(a) The peak voltage of an ac supply is 300 V. What is the rms voltage? (b) The rms value of current in an ac circuit is 10 A. What is the peak current?

7.3beginner🔧 Apply1 markNumerical

A 44 mH inductor is connected to 220 V, 50 Hz ac supply. Determine the rms value of the current in the circuit.

7.4beginner🔧 Apply1 markNumerical

A 60 $\mu$ F capacitor is connected to a 110 V, 60 Hz ac supply. Determine the rms value of the current in the circuit.

7.5intermediate💡 Understand2 marksShort Answer

In Exercises 7.3 and 7.4, what is the net power absorbed by each circuit over a complete cycle. Explain your answer.

7.6beginner🔧 Apply1 markNumerical

A charged 30 $\mu$ F capacitor is connected to a 27 mH inductor. What is the angular frequency of free oscillations of the circuit?

7.7intermediate🔧 Apply2 marksNumerical

A series $LCR$ circuit with $R = 20 \Omega$ , $L = 1.5$ H and $C = 35 \mu$ F is connected to a variable-frequency 200 V ac supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?