Electrical Energy and Power
5.5 Electrical Energy and Power
By the end of this section, you will be able to:
- Express electrical power in terms of the voltage and the current
- Describe the power dissipated by a resistor in an electric circuit
- Calculate the energy efficiency and cost effectiveness of appliances and equipment
Using Ohm’s Law in Resistor Circuits
Electrical Power in Circuits
In physics 1, you discussed mechanical power which is the rate at which mechanical work is done: .
The units for power are J/s, which are called Watts, symbol: W (but don’t confuse the unit W with the symbol for work, they’re not the same thing). Generally, power is the measure of how quickly energy is transferred into or out of a system.
Here we will discuss electrical power, which is also measured in J/s = W (watts). But instead of looking at how the kinetic energy or the gravitational potential energy changes, we will focus on how the electric potential energy changes in time.
|Household appliances (in the US) all have = 120 V.|
What is the approximate resistance of the filament (at operating temperature) of a 100 W lightbulb?
|US light bulbs are rated for 120 V. |
European bulbs are designed for 240 V.
If you buy a 100 W light bulb as a souvenir in Paris, and plug it in at home, what happens?