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Electric Power is the rate at which electrical energy is transferred by an electric circuit per unit of time. In simpler terms, electric power is defined as the rate at which the work is being done in an electrical circuit. Electric power is denoted by P. The SI Unit of electric power is Watt or one Joule per second. Electric power is produced by the generator and can also be supplied through electrical batteries. It can also be transferred to long distances with the help of transmission wires.
Read More: NCERT Solutions For Class 12 Physics Current Electricity
Key Terms: Electric Power, Electric Current, Potential Difference, Electric Circuit, Watt, Energy, Electric Power Formula, Ohm’s Law
Definition of Electric Power
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Electric power is the rate of electrical energy transfer by an electric circuit per unit of time. It is a measure of how much energy is being used in a particular period of time. Power is the rate at which work is done. In a similar manner, when it is done with respect to time and in an electrical circuit, it is referred to as electric power.
- The SI unit of measurement of electric power is watt (W).
- Electric power is denoted by P.
- Electric power is a scalar quantity.
- It can be produced in generators and then be supplied to electric batteries used in devices.
- Electric power gives a low entropy form of energy that is carried over long distances.
- It is converted into various other forms of energy like motion, heat energy, etc.
Electric Power
Unit of Electric Power
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The SI Unit of electrical power is watt (W).
- The power consumed in an electrical circuit is said to be one watt if one ampere current flows through the circuit when a potential difference of 1 volt is applied across it.
- Kilowatt (1000 watts) is used to denote a larger unit of electric power.
- Gigawatt and megawatt are also used for larger units of electric power.
Read More: Electricity Revision Notes
Electric Power Formula
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Electric Power can be calculated using the electric power formula. The electric power formula is as follows:
P = VI
Where
- P refers to Electric Power.
- V refers to the potential difference in the circuit.
- I refers to the electric current.
Using Ohm’s Law, Electric Power can also be written as
P = I2R
P = V2 / R
According to Ohm’s Law, the voltage across a conductor is directly proportional to the current flowing through it, keeping all the physical conditions and temperatures constant. Ohm’s Law states the relationship between voltage, current, and resistance as:
V = IR
The above-mentioned equations for electric power are derived from Ohm’s Law.
Electric Power Formulas
Solved ExampleExample: The current and voltage of an electric circuit are given as 2.5A and 10V respectively. What will be the electrical power? Solution: Given parameters are:
Using the Electric Power Formula, P = VI P = 10 × 2.5 = 25 watts Thus, the electric power is calculated as 25 watts. |
Read More: Important MCQs on Current Electricity with Explanation
Power-Energy Formula
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Electric power is the rate of energy consumption. Thus, energy can be calculated using the following formula:
\(P = {E \over t}\)
Where
- E denotes energy consumption in Joules.
- t denotes the time in seconds.
Electric Power can also be stated as:
\(P = {VQ \over t}\)
Where
- Q denotes the electric charge in Coulombs.
- V refers to the potential difference in volts.
- t denotes the time in seconds.
| Topics Related to Electricity | ||
|---|---|---|
| Electricity | Resistance Formula | Electrical Formulas |
| Difference Between Voltage and Current | Uses of Electricity | |
Things to Remember
- Electric Power is the rate of transfer of energy by an electric circuit.
- It is the rate at which the work is being done in an electrical circuit.
- Electric power is represented by P and the SI unit of electric power is watt (W).
- Electric power is produced through a generator. It can also be supplied by electrical batteries.
- It can be carried over long distances through transmission wires.
- Electric power is used for various purposes such as that in motion, light, or heat with high efficiency.
- Electric Power Formula is given as P = VI, where V is the potential difference in the circuit, and I refers to the electric current.
Previous Years’ Questions (PYQs)
- An electric bulb is rated 220 V and 100 W. What is the power consumed… (JKCET 2019)
- The power dissipated in 3Ω resistance in the following circuit is… (KCET 2017)
- Power dissipated across the 8Ω resistor in the circuit…
- Power dissipated in an LCR series circuit connected to an a.c. source… (NEET 2009)
- When a current is passed in a conductor, 3oC rise in temperature is…
- An installation consisting of an electric motor driving a… (VITEEE 2014)
- Two identical batteries each of e.m.f 2 V and internal resistance… (NEET 1990)
- The power dissipated in the circuit shown in the figure is…
- Total emf produced in a thermocouple does not depend on…
- Two heater wires of equal length are first connected in series…
Sample Questions
Ques. What will be the electric power of a circuit whose current is 3 Ampere and voltage is given as 10 volts? (3 Marks)
Ans. According to the question,
- Electric Current I = 3 Amp
- Potential Difference V = 10 volts
- Electric Power =?
Using Electric Power Formula,
P = IV
P = 3 x 10
P = 30 watts
Thus, the power of the circuit is 30 watts.
Ques. Define electric Power. What is the SI unit of electric power? (3 Marks)
Ans. Electric power is defined as the rate at which electrical energy is transferred in an electrical circuit per unit of time. In simpler terms, electric power tells how much energy is used in a particular span of time. The SI unit of electric power is watt (W).
Ques. Calculate the electric current and power across the resistor if a 9V battery is connected to a resistor having a resistance of 10 Ω. (3 Marks)
Ans. Given parameters are,
- Voltage V = 9V
- Resistance R = 10Ω
According to Ohm’s Law,
I = V/R
I = 9/10 = 0.9 A
Now, using Electric Power Formula,
P = VI
P = 9 × 0.9
P = 8.1 W
Ques. What is Electric Power Formula? (3 Marks)
Ans. Electric Power Formula is given as
P = VI
Where P denotes Electric Power, V refers to the potential difference and I denotes Electric Current.
Electric Power can also be calculated through these formulas:
- P = I2R
- P = V2/ R
Ques. What will be the power of an electrical circuit consisting of resistance 3Ω and a current 4A flowing through the circuit? (3 Marks)
Ans. Given that,
- Electric Current I = 4A
- Resistance R = 3Ω
Using the Electric Power Formula,
P = I2R
P = 42×3
P = 16×3
P = 48 watts
Thus, the power of the electrical circuit would be 48 watts.
Ques. A mobile battery functions at 12.0 V. It needs to provide a current of 0.9 A in case of playing music. What will be the power required for it? (3 Marks)
Ans. According to the question,
I = 0.9 A
V = 12.0V
Using Electric Power Formula,
P = VI
P = 12.0 V x 0.9 A
P = 10.8 W
Thus, the power required by the battery of the mobile phone is 10.8 W.
Ques. What are the types of electric power? (3 Marks)
Ans. There are two types of electric power:
- DC Power: DC power is the product of voltage and current and is produced by the fuel cell, battery, and generators.
- AC Power: There are three types of AC power- apparent power, active power, and real power.
- Apparent Power is the useless power or idle power.
- Active Power is the real power that is dissipated in the circuit resistance.
- Reactive Powe is the power developed in the circuit reactance.
Ques. An iron uses 18kJ energy for 2 minutes at a voltage of 250 volts. What will be the current in the iron? (3 Marks)
Ans. Given that,
- Time t = 2 minutes = 120 seconds
- Energy = 18 Kilojoule = 18000 Joule
- Voltage V = 250 V
Electric Power = P = W/t
P = 18000 Joule/120 seconds = 150 Watt
Thus,
Electric current (I) = P/V
I = 150 / 250 = 0.60 Ampere
Ques. In which unit is electric power measured? (2 Marks)
Ans. Electric power is measured in the units of Watts (W), which is named to honor James Watt, the inventor of the steam engine. A Watt is the SI unit of electric power which is equal to one ampere under the pressure of one volt.
Ques. What do you mean by power in a circuit? (3 Marks)
Ans. The power in a circuit is a measure of how quickly the energy is being converted. In an electrical circuit, some elements deliver power that is they convert energy into the electrical form whereas other elements absorb the power that is they convert energy from electrical energy into some other form.
Ques. What is an electric power supply? (3 Marks)
Ans. An electric power supply refers to an electrical device that supplies electric power to an electrical load. The main utilization of a power supply is to convert the electric current received from a source to the correct voltage, current, and frequency to power the load.
Ques. A laptop battery works at 24 V and needs to provide a current of 1.5 A while gaming. Calculate the power required for the same. (3 Marks)
Ans. Given that,
I = 1.5 A
V = 24 V
Using Electric Power Formula,
P = VI
P = 24 V x 1.5 A
P = 36 W
Thus, the power required by the battery of the laptop is 36 W.
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