Why alternating current over direct current

Resistance reduces the energy transmitted in a wire. By increasing the voltage on the wires to very high voltages for long distance transmission, this loss can be reduced. Increasing the voltages the grid transmits electricity reduces this lost power. As the voltage gets higher, the current decreases proportionally because the transmitted electrical power energy per unit time remains the same. However there is a limit, being that at extremely high voltages kV the electricity begins to discharge resulting in high losses.

Efficient transmission saves power companies and consumers a lot of money, which helps reduce pollution since power plants do not need to make up for lost electricity by using more fuel. Other advantages of AC include: [5]. A big advantage of direct current is that it is easier to change the speed of a DC electric motor than it is for an AC one. This is useful in many applications, such as electric and hybrid cars.

There are distinct advantages of AC over DC electricity. The ability to readily transform voltages is the main reason we use AC instead of DC in our homes. The major advantage that AC electricity has over DC electricity is that AC voltages can be readily transformed to higher or lower voltage levels, while it is difficult to do that with DC voltages.

Since high voltages are more efficient for sending electricity great distances, AC electricity has an advantage over DC. This is because the high voltages from the power station can be easily reduced to a safer voltage for use in the house. Changing voltages is done by the use of a transformer. This device uses properties of AC electromagnets to change the voltages.

AC electricity also allows for the use of a capacitor and inductor within an electric or electronic circuit. These devices can affect the way the alternating current passes through a circuit.

They are only effective with AC electricity. A combination of a capacitor, inductor and resistor is used as a tuner in radios and televisions. Without those devices, tuning to different stations would be very difficult.

The frequencies and peak voltages of AC sources differ greatly. Figure 2. The potential difference V between the terminals of an AC voltage source fluctuates as shown. Figure 2 shows a schematic of a simple circuit with an AC voltage source.

The voltage between the terminals fluctuates as shown, with the AC voltage given by. For this example, the voltage and current are said to be in phase, as seen in Figure 1 b.

If the resistor is a fluorescent light bulb, for example, it brightens and dims times per second as the current repeatedly goes through zero. A Hz flicker is too rapid for your eyes to detect, but if you wave your hand back and forth between your face and a fluorescent light, you will see a stroboscopic effect evidencing AC.

The fact that the light output fluctuates means that the power is fluctuating. Wave your hand back and forth between your face and a fluorescent light bulb. Do you observe the same thing with the headlights on your car? Explain what you observe. Warning: Do not look directly at very bright light. Figure 3. AC power as a function of time. Since the voltage and current are in phase here, their product is non-negative and fluctuates between zero and I 0 V 0. We are most often concerned with average power rather than its fluctuations—that W light bulb in your desk lamp has an average power consumption of 60 W, for example.

As illustrated in Figure 3, the average power P ave is. Similarly, we define an average or rms current I rms and average or rms voltage V rms to be, respectively,. In general, to obtain a root mean square, the particular quantity is squared, its mean or average is found, and the square root is taken. This is useful for AC, since the average value is zero.

It is standard practice to quote I rms , V rms , and P ave rather than the peak values. The common A circuit breaker will interrupt a sustained I rms greater than 10 A. Your 1. You can think of these rms and average values as the equivalent DC values for a simple resistive circuit.

DC power is far more consistent in terms of voltage delivery, meaning that most electronics rely on it and use DC power sources such as batteries. Electronic devices can also convert AC power from outlets to DC power by using a rectifier, often built into a device's power supply. A transformer will also be used to raise or lower the voltage to a level appropriate for the device in question. Not all electrical devices use DC power, though.

Many devices, household appliances, especially, such as lamps, washing machines, and refrigerators, all use AC power, which is delivered directly from the power grid via power outlets. Although many of today's electronics and electrical devices prefer DC power because of its smooth flow and even voltage, we could not get by without AC. Both types of power are essential; one is not "better" than the other.

In fact, AC dominates the electricity market; all power outlets bring power into buildings in the form of AC, even where the current may need to be immediately converted into DC power. This is because DC is not capable of traveling the same long distances from power plants to buildings that AC is.