Electric Power
Master Electrical Power Calculations in Minutes: Learn how electrical energy is consumed by appliances and converted into heat, light, or mechanical work. Master the core algebraic formulas for electric power, understand the commercial unit of electricity (the kilowatt-hour), and learn to compute household electricity bills without complex notation.
1.0Learning Outcomes
After completing this lesson, you will be able to:
- Define electric power and its standard SI unit.
- Derive and apply the three core mathematical equations for power (P = VI, P = I2R, P =V2/R).
- Define 1 Watt of power in terms of voltage and current.
- Distinguish between electrical power and electrical energy.
- Convert commercial energy units (kWh) into standard Joules (J).
- Solve numerical problems based on power ratings and household energy consumption.
2.0Definition
The work done per unit time by a source of emf (like a battery) in order to maintain electric current in a circuit is called ‘electric power’.
Consider a current I flowing through a resistor of resistance R. Let the potential difference across it be V (in figure). Let t be the time during which a charge Q flows across. The work done in moving the charge Q through a potential difference V is given by,
W = Q × V … (1)
(V=QW)
Thus, the power input to the circuit by the source is
P=tW=tQ×V=(tQ)×V=I×V
or P=VI
3.0Unit of Electric Power
SI unit : Watt
Here, 1 Watt = 1 volt-ampere = 1 VA
1 kilowatt = 1000 watt
If the electric current through a device is one ampere and the potential difference across it is one volt, then its electric power is one Watt.
Also, power consumed by a resistor can be written as,
P=VI=RV2=I2R [Using, I= V/R and V=IR]
Every electric device is mentioned with a specified power and a specified voltage ; it works properly only if it runs at the specified voltage.
A 100-watt electric light bulb uses 100 joules of electrical energy every second.
If applied voltage is greater than specified voltage for an electric device, then the actual current exceeds its current capacity, the device will get damaged. If applied voltage is less than the specified voltage, then the current in the circuit will be less than the required; the device will not work properly.
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5.0Supporting Study Materials
This study material CBSE Notes and NCERT Solutions for the Chapter "Electricity" on Electric Power Topics is designed according to the latest CBSE Class 10 Science syllabus and NCERT guidelines. It provides clear explanations of key concepts, definitions, formulas, and important questions to help students understand electric power, heating effects of electric current (Joule's heating), commercial units of electrical energy, and prepare effectively for examinations.
6.030 Second Quick Revision
Resistance (R) – Opposition offered by a conductor to the flow of current.
🔹 Factors Affecting Resistance
- Directly proportional to length (L)
- Inversely proportional to area (A)
- Depends on material (ρ)
🔹 Series Combination
- Same current flows through all resistors.
- Total Resistance = R₁ + R₂ + R₃
🔹 Parallel Combination
- Same voltage across each resistor.
- 1/R = 1/R₁ + 1/R₂ + 1/R₃
🔹 Electric Power
- Rate at which electrical energy is consumed.
- Power = Voltage × Current
- Unit: Watt (W)
🔹 Heating Effect of Current
- Heat produced = I²Rt
- Used in heaters, irons, geysers, etc.
7.0Recommended Next Topics
- Magnetic Effects of Electric Current (Electromagnetic Induction)
- Heating Effects of Electric Current (Joule's Law of Heating)
- Resistors in Series and Parallel Combinations
- Domestic Electric Circuits (Fuses and Grounding)