The following formulas are used to calculate electric power, depending on the known quantities:
Power Formulas and Their Applications
Here's a breakdown of the power formulas commonly used in Class 10 physics, along with when to apply each one, based on the provided references:
| Formula | Description | When to Use | Reference |
|---|---|---|---|
| P = VI | Power = Voltage × Current | Use when you know the voltage and current in a circuit. | [1] |
| P = I2R | Power = (Current)2 × Resistance | Use when you know the current and resistance in a circuit. | [2] |
| P = V2/R | Power = (Voltage)2 / Resistance | Use when you know the voltage and resistance in a circuit. | [2] |
| P = E/t | Power = Energy / Time | Use when you know the energy consumed and the time taken. This is a general power equation. | [3] |
Examples and Practical Insights
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Example 1: A light bulb has a voltage of 220V and a current of 0.5A. To find the power consumption, use P = VI. P = 220V * 0.5A = 110W.
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Example 2: A resistor has a current of 2A flowing through it, and its resistance is 10 ohms. To calculate the power dissipated by the resistor, use P = I2R. P = (2A)2 * 10Ω = 40W.
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Example 3: A heating element with a resistance of 20 ohms is connected to a 120V supply. To calculate the power consumed by the heating element, use P = V2/R. P = (120V)2 / 20Ω = 720W.
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Example 4: An electric motor consumes 3600 Joules of energy in 2 minutes (120 seconds). To find the power rating of the motor, use P = E/t. P = 3600J / 120s = 30W.
Key Considerations:
- The formulas P = I2R and P = V2/R are derived from Ohm's Law (V = IR) and the basic power formula P = VI. They are useful when you don't have both voltage and current directly.
- The formula P = E/t is a general definition of power and applies broadly, not just to electrical circuits.
