[Physics Class Notes] on Electric Power Pdf for Exam

Electric power refers to the rate per unit of time at which the electric energy is transferred by the electric circuit. If we talk about a unit of power, it is Joule per second or Joule per unit time. It is usually supplied to the homes or in the domestic mains’ electric supplies or in the offices. Electric power can be transferred to long distances with the help of transmission wires. This electric power is used for a number of purposes such as that in motion, light or heat with high efficiency. 

Usually, electric power is produced by electric generators but they can be supplied to the source where it is needed with the help of the electric batteries. Electric power can be transferred to another form of energy when electric charges travel through a distance, which is popularly known as voltage. This basically occurs in electric components in the electric circuit. And on the basis of electric power, the circuits of electricity are further divided into two types. Those are active devices and passive devices. 

Active devices are the sources of power while passive devices are the loads. You need to understand the law of electric power, which is the Ohm’s law. For the current to travel there is resistance also across the length of the wire test. It further depends upon different factors such as temperature, length of wires and so on. All the formulas,  definitions, properties and other information need to be learnt well by the students. 

What is Meant by Electric Power?  

Power is commonly defined as the rate at which the work is done. When this is done with respect to time and in an electrical circuit, it is known as electric power. Alternately, electric power is defined as the rate at which electric energy is transferred across an electrical circuit per unit time. Electric power is versatile – it can be produced in generators in our houses and can be supplied to electric batteries used in devices.

Unit of Electric Power

When you push or pull something through some distance, you do some work, and it is represented by Unit Joule. Power is actually the rate at which any work is done. It is the rate at which work is done or how fast some work is done. It is the derived unit in the metric system. The Unit of Electrical Power is Watt. One Watt is one Joule of work being done on an object per second. It is defined  in Joule per second. Watt is represented as W. If you do 75 Watts of work per second, it means you do 75 joules of work every second. When we calculate power, we simply  consider the work and the amount of time it takes to do  that work. 

Voltage is the electromotive force or potential difference between two points, which signifies the amount of work required to move a charge between two points. The unit of voltage is Volt. Ampere is represented by A and is the unit of electric current. 

The power consumed in an electric circuit is known as one Watt when one ampere of current is seen flowing through that electrical circuit.

In this case, the potential difference of 1 volt is applied across it. 

If you want to denote a larger unit of electric power, you can use kilowatt (equal to 1000 watts).

You can also use gigawatt and megawatt for larger units of electric power.

The Formula of Electric Power

To calculate power, the most simple equation is work done divided by time.

(1) P = W/t

W is work done; t is time

However, the above expression is used mostly for mechanical power. For electric power, another equation is used, when we calculate work through the amount of charge and the potential difference through which the charge is moving. 

(2) W = qV 

Where q = total charge used and V = voltage

When we substitute (1) in (2), we understand that power is now the charge multiplied by the voltage divided by the time.

(3) P = qV/t

Additionally, we know that current is the charge per second that passes through the circuit at any given point in time. 

(4) q = It

Where q = total charge and I = current (ampere)

Now, when we substitute (4) in (3), we understand that power is actually the current multiplied by time multiplied by voltage, divided by time. In this case, time gets cancelled from the numerator and denominator, to give us the final equation, which is :

P = IV

Here, P is the power, V or voltage is the potential difference in the circuit, and I is the electric current.

Power can also be written as

P = V²/R or I²R

Where V is the voltage, R is the resistance, and I is the electric current.

These can be obtained when we apply the Ohms law, which says that electric current is proportional to voltage and inversely proportional to resistance.

Electric Power Problems and Answers

Q1. A 280 V – 10 A electric lamp is used for 30 minutes. How much energy does it require?

Ans: In the above question, 

V or Voltage = 280 Volt

I or electric power = 10 Ampere

T or Time = 30 minutes = 30 x 60 seconds = 1800 seconds

So, Electric power can be calculated.

P = IV

P = 10 x 280

P = 2800 Volt Ampere = 2800 Watt = 2800 Joule/second

However, electric energy is Electric power multiplied by time.

Electric Energy = P x t = 2800 Joule/second x 1800second = 5040000 Joule

= 5040 KiloJoule

Q2. The energy used by the iron for 2 minutes is 18 kJ, at a voltage of 250 volts. How large is the current in the iron?

Ans: Here, t = 2 minutes = 120 seconds

Energy = 18 Kilojoule = 18000 Joule

Voltage = 250 V

Electric power = P = W/t = 18000 Joule/120 seconds = 150 Watt

Therefore, Electric current (I) = P/V = 150 / 250 = 0.60 Ampere

Conclusion

Here in this article, you will learn about the definition of electric power. Here the unit of electric power is explained in detail, along with this, you will come across the formula P of electric power. There are some solutions and problems for you to solve in order to understand the topic of Electric Power well. At the end of this article, you will come across a few Frequently Asked Questions that will keep you updated with the questions that are frequently asked about these topics.