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Power is a term that is used on a daily basis in different aspects of life. Generally, it is considered a synonym for strength or energy. Imagine that there are two friends and one person’s bike has much more power than the other’s. What does that specifically mean? If you think it’s the strength, speed, or weight of the bike, you are completely wrong.
Let’s get started and understand what power means in science.
Definition of Power
Power is defined as the ratio of work to the total time taken. This is the standard definition of power, but we can define it in various forms.
The amount of energy required by the machine to work can be termed the power of the machine.
It can also be defined as follows:
Power is the rate at which energy is consumed.
Unit of Power
The standard unit to measure power is the watt (W).
It is measured in watts with the help of the formula P= QV/t. So likewise, it’s the electric charge in Q coulombs and voltage in V with time in t seconds. The solution of this equation will give the value of power in watt W.
Another unit of power is horsepower (hp).
You must have noticed that this unit of power is often used in automobiles, motorbikes, cars, etc.
1 hp = 746 W
Measurement of Power
As we have discussed, according to the standard definition of power, the formula of power is as follows:
P = W/t
That is, the amount of work done is divided by the total time taken in seconds.
That means one watt is equal to one joule of work done per second.
P = ∆E/∆t
In the above formula, ∆E is the change in energy which is measured in joules, and ∆t is the total time taken measured in seconds.
In different types of circuits having resistance, power is measured using ohm’s law.
P = I2×R = V2/R
In the above formulae, “I” is the current in the circuit, V is the voltage, and R is the resistance in the circuit.
However, power is not constant all the time. It varies, and in that condition, the above formulae will not work. Hence, the formulae of power in this condition is as follows:
P(t) = I(t) × V(t)
Here, I is the current and V is the voltage in the circuit.
Types of Power
Power can be expressed in three different ways.
- Average power – Power is said to be the average power when it is measured over a long period of time. It is calculated graphically by the area under the power vs. time curve divided by the total time.
- Instantaneous power – When power is measured for a given instant of time, then it is said to be instantaneous power. In this way, ∆t in the formula of power is very low. It is measured with the help of a power vs. time graph.
- Peak power – It is the maximum value of power measured at any instant of time over a long period of time.
Difference Between Power and Energy
It’s very important to understand the difference between power and energy. This is because people are usually confused between the two and end up considering them to be the same.
Energy is something that cannot be felt or touched, but it can be experienced when it is transferred from one place to another or from one form to another.
And if you do understand the basics of energy, then power is simple: the rate at which energy is transferred from one place to another.
The standard unit of energy is joule and the standard unit of power is watt. So we can say that watt is equal to joule per second.
Let’s take an example.
Suppose you are using your laptop, and it is consuming 20 joules per second. Then the power of the laptop at that instant will be 20 watt.
Power Consumed by AC Circuit
When it comes to power consumption in an AC circuit, it is measured differently.
Power in an AC circuit can be defined as the amount of energy transferred by the circuit per second.
Power Factor
In this case, the power factor is defined as the ratio of true power with respect to apparent power. Power factor falls in the range of 0 to 1. This means that the power factor is always positive, but also not more than 1.
Power factor is denoted by cos 𝛉 = R/Z
Here R is the resistance in the circuit and the Z, as we know, is the impedance of the circuit.
Value of power factor, i.e., cos 𝛉 = 1 when resistance is pure. But when the capacitor is pure or the inductor is pure, the value of cos 𝛉 is 0.
Important Formulas to Remember
Power consumption for RC circuit:
cos 𝛉 = R /( √R2 + 1/ ⍵2C2)
Power consumption for LR circuit:
cos 𝛉 = R /√R2 + L2⍵2
Power consumption for LCR circuit:
cos 𝛉 = R /√R2 + (L⍵ – 1/C⍵)2
Conclusion
In this article, we have discussed power and its consumption. The standard unit of power is the watt, and it is the ratio of work done and the total time taken. We have also discussed different ways to calculate power in different aspects like for RC, LR, and LCR circuits. The difference between power and energy should be clear now, as power is simply the rate of transfer of energy.
