# Alternating Currents | Old is Gold | XII

#### Short Questions

1. Why do we prefer a choke coil to rheostat in an a.c. current?

2. What is meant buy independence of an a.c. current?

3. Why is choke coil preferable to resistor?

4. Why is choke considered superior to a rheostat?

5. What do you mean by r.m.s value of an AC current?

6. What is meant by wattles current?

7. Fluorescent tubes often use an inductor to limit the current through the tube. Why is it better to use inductor than a resistor for this purpose?

8. Why is a choke coil better than a resistor ina n electrical appliences?

9. Define rms value of alternating current.

10. What are the advantages of a.c. over d.c.?

11. A chock coil is preferred to a resistor in an ac current. Why?

#### Long Questions

1. Discuss the phase relationship between the voltage and current in the ac current containing inductance and resistance. What is power factor of the circuit?

2. Find the impendence of LCR circuit in series.

3. An alternating emf is applied across a capacitor. Show that the current in its leads to the applied emf by 90°.

4. An a.c. passes through a circuit containing a resistor and a inductor in series. Derive an expression for the phase relation between the current and the voltage.

5. Discuss the phase relationship between the voltage and current in the a.c. circuit containing capacitor and resistor in series and hence derive an expression for the impedance of the circuit.

6. Derive the condition for resonant frequency of an LCR alternating current series circuit.

7. Derive an expression of current flowing through a.c. circuit containing a resistor and capacitor in series combination. What is the power factor of this circuit?

8. Discuss the phase relationship between the circuit and voltage in a.c. circuit containing capacitor and resistor in series and hence derive an expression for the impedance of the circuit.