What is an Alternating Current?
Based on the direction of current flowing through the circuit, it is differentiated in two types. One is Alternating current and another is Direct current. When an electric current reverses its direction periodically while flowing through an electric circuit is called Alternating Current (AC). On the other hand, when current flows in only one direction is known as Direct current (DC).
The major advantage of alternating current is that AC voltages can be easily transformed from higher to lower voltage levels and vice-versa. Due to this virtue, high voltage power from power stations can be reduced to a safer voltage for domestic use. Only Alternating current is compatible with capacitors and inductors. By using them within the Alternating current circuits, the flow of electricity can be turned. This property helps tune the radio stations. Because of these reasons, AC electricity is most preferred for home appliances.
Power Consumed in an AC Circuit
An electric circuit produces power which is given by the expression, P= I V.
Where, I – the current flowing through the circuit and
V- Voltage across it.
AC circuits always offer reactance, therefore there are two components of power, a power component because of the magnetic field and another because of the electric field. The average power absorbed by the circuit becomes the sum of power stored and returned through a complete one cycle. Thus, the average power consumed by the circuit will be the instantaneous power within one cycle.
Power Factor
The power factor of an alternating current is defined as the ratio of the true power flowing through the circuit to the apparent power present in the circuit.
It is usually in the interval of -1 to 1 and is dimensionless.
Power Factor = \[\frac{ \text {True power}}{\text{Apparent power}}\]
Also, cosΦ = \[\frac{R}{Z}\]
R- resistance in the circuit
Z- impedance of the circuit.
Definition of Power in AC Circuit
The rate of doing work or the amount of energy transferred by a circuit per unit time is known as power in AC circuits. It is used to calculate the total power required to supply a load. Power factor: In an AC circuit, the power factor (PF) is defined as the ratio of real power (P) to apparent power (S). The PF can be expressed in percent or decimal form.
The Importance of Power in an AC Circuit
The power in an AC circuit is very important as it determines the amount of current that flows through the circuit and hence, the size of the wire required. The voltage and current waveforms are also affected by the power factor. A low PF means that a lot of energy is being wasted in the form of heat due to poor utilization of electricity. This can cause overheating and failure of electrical equipment.
The Importance of the Power Factor
The power factor is very important as it determines the amount of current that flows through the circuit and hence, the size of the wire required. The voltage and current waveforms are also affected by this factor. A low PF means that a lot of energy is being wasted in the form of heat due to poor utilization of electricity which can cause overheating and failure of electrical equipment.
Here are Some Tips to Study the Power in AC Circuit
Knowing how to solve simple AC circuit problems helps you learn more about PF and its applications in real-life situations. Some examples include finding the reactive watts, total watts, current, and voltage for a given power factor. These examples can help you learn more about PF and its applications in real-life situations. Here are some tips to study the Power Factor:
Know the basics- It is important to know the basics of an AC circuit before studying the power factor. So that, you can easily understand the importance and applications of the power factor. Solve simple problems- Knowing how to solve simple AC circuit problems helps you learn more about PF and its applications in real-life situations. Some examples include finding reactive watts, total watts current, or voltage for a given power factor. Learn from textbooks - Textbooks contain detailed information on formulas along with solved examples.
Practice more problems- Practicing a lot of examples is one of the most effective ways to learn and understand the concept of the power factor which will help you to use the power factor in real-life problems.
Understanding and applying PF concepts is an important part of learning more about electrical equipment and devices that implement it.
Studying examples from textbooks along with practicing lots of problems helps one learn quickly as well as understand PF better which ensures correct usage in real-life situations.
Appear for mock tests- Mock tests help you understand where you stand with the concept of power factor. Last but not least, appearing for mock tests gives one an idea about how much they have learned about power factors and what all they need to focus on.
Learn the rules- It is important to learn the rules of the power factor before solving any problem.
Fun Facts
Ohm’s law for the RMS value of an alternating current is calculated by dividing the RMS voltage by the impedance.
The average power delivered to an LCR circuit varies with the phase angle.
FAQs on Power in AC Circuit
1. What is the power factor in an AC circuit and how does it influence energy efficiency in electrical devices?
The power factor in an AC circuit is the ratio of true power (actual power consumed) to apparent power (total power supplied). A high power factor means electrical energy is used more efficiently, minimizing energy wastage as heat. A low power factor leads to greater losses, possible overheating, and higher electricity costs in devices.
2. How is the average power calculated in an LCR AC circuit according to the CBSE 2025–26 syllabus?
The average power supplied to an LCR circuit is calculated using the formula P = VI cosΦ, where V and I are the root mean square (RMS) values of voltage and current respectively, and Φ is the phase angle between them. This clearly quantifies real energy delivered over one complete cycle.
3. Why is alternating current (AC) preferred over direct current (DC) for transmission of electric power?
Alternating current (AC) is preferred for transmission because it can be easily converted to higher or lower voltage using transformers, reducing energy loss over long distances. Higher transmission voltages mean lower currents, which reduces heat loss in wires and makes AC more suitable for household and industrial distribution.
4. What happens if the power factor in a circuit is low? How does it affect current and electrical equipment?
A low power factor causes more current to flow through a circuit for a given load, leading to excessive heating of conductors and possible failure of electrical equipment due to overload. It also means more energy is wasted, increasing operational costs and reducing equipment lifespan.
5. How do you determine the true, apparent, and reactive power in an AC circuit?
- True Power (P): Power actually consumed by the resistance, given by P = VI cosΦ.
- Apparent Power (S): Total power supplied, S = VI.
- Reactive Power (Q): Power stored and returned by inductors/capacitors, Q = VI sinΦ.
6. Can you explain the significance of phase angle in AC circuits and its effect on power calculation?
The phase angle (Φ) represents the difference in phase between voltage and current in an AC circuit. When Φ = 0°, power factor is 1 (all power is useful). As Φ increases, less power is converted to usable energy, reducing efficiency. Accurate power calculation in AC depends on considering this phase difference.
7. What common mistakes should students avoid when solving AC circuit power questions in board exams?
Students should avoid:
- Confusing RMS and peak values for voltage/current.
- Ignoring the phase angle (Φ) in power calculations.
- Using the power formula P = VI without multiplying by cosΦ.
- Misidentifying apparent vs. true power in their answers.
8. How does improving power factor benefit industries and households?
Improving the power factor lowers the total current drawn by electrical devices, thereby reducing losses, minimizing utility bills, preventing equipment overheating, and ensuring compliance with electricity regulations. Industries may incur penalties for low power factor, making its correction essential for cost savings.
9. What steps should students follow to master the concept of power in AC circuits for the board exam?
To excel in this chapter:
- Start by understanding fundamental definitions and concepts like true, apparent, and reactive power.
- Practice solving a variety of numerical questions using standard formulas.
- Draw and analyze phasor diagrams for clarity of phase relationships.
- Attempt previous years’ board questions to gauge exam trends.
- Regularly attempt mock tests for self-assessment and time management.
10. How is Ohm’s Law modified for AC circuits and what role does impedance play in determining power?
In AC circuits, Ohm’s Law is expressed as Vrms = Irms × Z, where Z is the impedance (combined effect of resistance, inductance, and capacitance). Impedance affects both the magnitude of current and the phase angle, which are critical for calculating average power in AC circuits.
