Electric Power Chapter 19-3

When a battery is used to maintain an electric current in a conductor, chemical energy stored in battery is continuously converted to the electrical energy of the charge carriers. Energy Transfer

As the charge carriers move through the conductor, this electrical energy is converted to internal energy due to collisions between the charge carriers and other particles in the conductor. Energy Transfer

Electric power, then, is the rate at which charge carriers do work Electric power, then, is the rate at which charge carriers do work. Put another way, electric power is the rate at which charge carriers convert electrical potential energy to nonelectrical forms of energy. Energy Transfer

P = W = ΔPE Δt Δ t Potential difference is defined as the change in potential energy per unit of charge: ΔV = ΔPE q Energy Transfer

This equation can be rewritten in terms of potential energy: ΔPE = ΔqV We can then substitute this expression for potential energy into the equation for power P = ΔPE = ΔqV Δt Δt Energy Transfer

Because current, I, is defined as the rate of charge movement (q/Δt), we can express electric power as current multiplied by potential difference: P = IΔV Power = current x potential difference Energy Transfer

This equation describes the rate at which carriers lose electrical potential energy. In other words, power is the rate of conversion of electrical energy. Energy Transfer

We learned that the SI Unit of power is the watt, W We learned that the SI Unit of power is the watt, W. In terms of the dissipation of electrical energy, 1W is equivalent to 1J of electrical energy being converted to other forms of energy per second. Energy Transfer

Most light bulbs are labeled with their power ratings Most light bulbs are labeled with their power ratings. The amount of heat and light given off by a bulb is related to the power rating (wattage). Energy Transfer

The conversion of electrical energy to internal energy in a resistant material is called joule heating. Energy Transfer

Power companies charge for energy, not power Power companies charge for energy, not power. However, the unit of energy used by electric companies calculate consumption, the kilowatt-hour is defined in the terms of power. 1kW-hour is the energy delivered in 1 hr at the constant rate of 1 kW. Energy Transfer

The following equation shows the relationship between the kilowatt-hour and the SI Unit of energy is the joule: 1kW-h x 103W x 60min x 60s = 1 kW 1 hr 1min 3.6 x 106W*s or 3.6 x 106J Energy Transfer

The electrical energy supplied by power companies is used to generate currents, which in turn are used to operate household appliances. This can be done by decreasing either current or resistance. Energy Transfer

When transporting electrical energy by power lines, power companies want to minimize the loss and maximize the energy delivered to a consumer. Energy Transfer

Although wires have little resistance, recall that resistance is proportional to length. So resistance becomes a factor when power is transported over long distances. Energy Transfer

Even though power lines are designed to minimize resistance, some energy is lost due to the length of the power lines. Energy Transfer

Thus transferring electrical energy at low currents, thereby minimizing the loss, requires that electrical energy be transported at very high potential differences. Energy Transfer

Power plants transport electrical energy at potential differences up to 765,000V. This is reduced by a transformer in your town to about 4000V. Energy Transfer

At your home, this potential difference is further reduced to about 120V by the transformer. Energy Transfer