GCSE Physics Tutorial: Applying Electrical Work Equations E=Pt and E=QV
In electrical circuits, work is done when electrical energy is transferred from one form to another. Two important equations used to calculate electrical work are E=Pt and E=QV. In this tutorial, we will learn how to apply these equations to solve practical problems related to electrical work.
1. E=Pt Equation: The equation E=Pt represents the electrical work done (E) when a device consumes electrical power (P) for a certain time (t). This equation is particularly useful when calculating the total energy consumption of an electrical device over a specific period.
Application Example 1: Calculating Energy Consumption of a Device Suppose an electrical appliance has a power rating of 500 watts (W) and is used for 4 hours. Calculate the total electrical energy consumed by the device.
Solution: Using the E=Pt equation: E = P × t E = 500 W × 4 hours E = 2000 watt-hours (Wh) or 2 kilowatt-hours (kWh)
The electrical device consumes 2000 Wh or 2 kWh of energy during 4 hours of operation.
2. E=QV Equation: The equation E=QV represents the electrical work done (E) when a charge (Q) moves through a potential difference (V). This equation is valuable when dealing with situations involving the transfer of charge and potential difference.
Application Example 2: Calculating Work Done in Charging a Capacitor A capacitor with a capacitance of 100 microfarads (μF) is charged to a potential difference of 12 volts (V). Calculate the work done in charging the capacitor.
Solution: Using the E=QV equation: E = Q × V Given that Q = C × V (charge is the product of capacitance and potential difference) E = (100 μF) × (12 V) E = 1200 microjoules (μJ) or 1.2 millijoules (mJ)
The work done in charging the capacitor is 1200 μJ or 1.2 mJ.
3. Energy Units Conversion: Watt-hour (Wh) and kilowatt-hour (kWh) are commonly used energy units in practical applications. These units can be converted as follows: 1 kilowatt-hour (kWh) = 1000 watt-hours (Wh) 1 kilowatt-hour (kWh) = 3.6 million joules (J)
Summary: Applying the electrical work equations E=Pt and E=QV allows us to calculate the total energy consumption of electrical devices and determine the work done in charge transfer situations. These equations are essential in understanding and analysing electrical circuits and devices, and they provide valuable insights into energy usage and efficiency. By mastering these concepts, you can solve practical problems related to electrical work and make informed decisions to optimise energy consumption.
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