Voltage can be changed in alternating current through the use of a transformer. The device uses electromagnets to create a magnetic field that can raise or lower the voltage as the current passes through it. By stepping the voltage down, the alternating current can be used for a variety of applications such as household electric appliances. Other applications can be accomplished by stepping up the voltage, including the long-distance transmission of power.
Electricity flows when electrons move from one location to another. Electrons move from positive to negative. This explains the flow of direct current. The terminal at the end of the wire carrying the current will remain negative and the current will flow in that direction. In alternating current, the terminal will switch between negative and positive. This causes the flow to reverse with this change. The rate of change is represented with units called hertz (Hz).
A Bhatia, a mechanical engineer who has worked on energy management projects for the United Nations, notes that a major disadvantage of direct current is loss of energy when making changes in the current. To reduce voltage in direct current, a resistor must be put in the circuit and the excess energy is lost. When transporting direct current, the resistance of the wire causes loss of energy. Alternating current can be transported more efficiently by using a transformer to step up voltage and lower current. This cannot be done with direct current.
The flow of electricity is measured in amperes. An ampere is determined by the number of electrons passing a given point in one second. In direct current, this is measured by the electrons moving in one direction. In alternating current, the electrons are measured moving in one direction for a half a second and then in the opposite direction in the next half a second.
Some applications, such as light bulbs, will function efficiently with either direct or alternating current. Other applications are more sophisticated, and alternating current is more suitable. Devices can be added to form a complex electrical circuit and allow new applications. This will affect the way a current passes through the circuit. Devices can be added to allow manipulation of the circuit for such applications as receiving radio or television signals. The low voltages possible with alternating current makes such applications feasible.
While alternating current is used for most applications, direct current is still more practical in some cases. A common use of direct current is in automobiles. Power is produced by a car's generator or alternator. This power is then stored in the car's battery. The battery holds the charge because of lead plates and sulfuric acid. The charge then can be used to operate such things as the vehicle's lights and radio.