Directions : In the following questions, A statement of Assertion (A)...
If resistor is used in controlling ac supply, electrical energy will be wasted in the form of heat energy across the resistance wire. However, ac supply can be controlled with choke without any wastage of energy. This is because, power factor (cosf) for resistance is unity and is zero for an inductance. [P = EI cosf].
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Directions : In the following questions, A statement of Assertion (A)...
Assertion: Choke coil is preferred over a resistor to adjust current in an AC circuit.
Reason: Power factor for inductance is zero.
Explanation:
To understand why a choke coil is preferred over a resistor to adjust current in an AC circuit, we need to understand the concept of power factor and the behavior of inductance in an AC circuit.
Power Factor:
Power factor is the ratio of real power (active power) to apparent power in an AC circuit. It represents the efficiency of the circuit in converting electrical power to useful work. Power factor is denoted by the symbol 'pf' and its value ranges between 0 and 1.
Inductance in an AC Circuit:
Inductance is the property of a circuit element (inductor) that opposes changes in current flowing through it. In an AC circuit, the inductance causes a phase shift between the voltage and current waveforms, which leads to a lagging power factor.
Explanation of Assertion and Reason:
- The assertion states that a choke coil is preferred over a resistor to adjust current in an AC circuit.
- The reason given for this assertion is that the power factor for inductance is zero.
Why Choke Coil is Preferred:
1. A choke coil, also known as an inductor, is a passive electrical component that stores energy in its magnetic field.
2. When current flows through a choke coil, it builds up a magnetic field around it.
3. The inductor opposes changes in current by inducing a back EMF (electromotive force) in the circuit, which reduces the rate of change of current.
4. As a result, the choke coil limits the flow of current in the circuit.
5. Unlike a resistor, which dissipates energy in the form of heat, a choke coil does not dissipate significant power and can handle high currents without overheating.
6. Therefore, a choke coil is more suitable for adjusting current in an AC circuit without causing excessive power loss.
Power Factor for Inductance:
1. In an AC circuit, the inductor causes a phase shift between the voltage and current waveforms.
2. The voltage across an inductor lags behind the current by 90 degrees in an ideal inductor.
3. Due to this phase shift, the power factor for inductance is zero.
4. This means that the inductive load does not consume any real power and only contributes to the reactive power in the circuit.
5. Reactive power represents the power that oscillates between the source and the inductive load without being consumed.
Conclusion:
- The power factor for inductance is indeed zero, as stated in the reason.
- However, the reason alone does not explain why a choke coil is preferred over a resistor to adjust current in an AC circuit.
- The preference for a choke coil is primarily due to its ability to limit current flow without dissipating significant power, making it more suitable for adjusting current in an AC circuit.