Dancing Electrons: The Basics of Electricity
We Take It for Granted
Look around the room. How many objects, devices, or appliances require electric energy to operate? What happens to our daily lives when we suffer a power outage? Americans are very dependent on electricity. We often take this invisible force for granted. Where does it come from? Who makes it? Electrical energy is produced by converting some other form of energy into electricity. For example, some power plants convert the force of steam into mechanical energy, which causes a turbine to rotate. The turbine is connected to an electrical generator that produces current. Electrical current travels along wires to our homes and businesses.
Current
An electrical current is the flow of electrons through a wire. Electrons can travel within a wire because they are free to move throughout the atomic network. Current, abbreviated I, is measured in amperes (A, or amp). One ampere of current equals 1 coulomb (6.25 billion billion electrons) flowing past a point in 1 second. Current travels differently in different materials. Some materials are good conductors; that is, the current travels easily through them. Copper, silver, and aluminum are examples of good conductors. Insulators are materials through which a current cannot travel.
Resistance
The ability of a current to travel through a material depends on that material's resistance, or opposition, to the flow of electrons. Resistance is abbreviated as R and is measured in units called ohms. The resistance of an electrical wire depends on the material from which the wire is made, its length, thickness, and temperature. Electrons can travel more easily along a thick wire than a thin one. Long wire offers more resistance than short wire. The filament in a light bulb is a thin wire that offers a lot of resistance to the flow of electricity. As the electrons attempt to travel through this filament wire, they heat up producing light and heat. The lamp cord, on the other hand, has very low resistance and remains cool while electricity travels along it.
People can be electrocuted or shocked because they accidentally lower the resistance of their body to the flow of electric current. Normally, when our skin is very dry, our bodies have a resistance of about 50,000 ohms. However, if we are wet, our resistance drops sharply to about 100 ohms. Normal household current can be very dangerous to a person standing in a puddle of water because wet skin conducts current well, and it can travel easily through our bodies to the ground.
Voltage
Not all electrical current has the same amount of push or strength. The amount of electricity available to push electrons along a wire is the voltage (V) or potential difference. When each electron traveling along a wire carries a lot of energy, the voltage is high. However, if each electron is only carrying a little energy, the voltage is low.
The current in a wire can be determined by dividing the voltage of electricity in that wire by the resistance of the wire. This rule, called Ohm's Law, is stated as:
I = V/R
To determine the amount of current flowing through a wire that has a resistance of 25 ohms when voltage is 50, divide 50 volts by 25 ohms:
I = V/R
I = 50 volts/25 ohms
I = 2 amps
Notice that current is expressed in amps, or amperes.
Direct Current
Electrical currents are produced in various ways. DC, or direct current, is produced by dry-cell batteries, wet-cell batteries, and thermocouples. Flashlight batteries are dry-cell types that change chemical energy to electrical energy. Zinc casing around the battery surrounds a paste made of various chemicals. This zinc casing serves as a negative pole for the battery. A carbon post in the center serves as a positive pole. Chemical reactions between the paste and the zinc cause electrons to build up around the zinc pole. If the two poles are connected by a wire, electrons will flow from the negative to the positive pole. If the wire contains a small light, electrons will flow through that light bulb filament and cause it to give off heat and light.
Wet-cell batteries operate in a similar fashion. Your car battery is a wet-cell battery composed of two metal poles (electrodes) and an acid (electrolyte). The chemical reaction between the acid and the metal at the negative pole causes an accumulation of electrons. A wire between the two poles allows electrons to flow, producing an electric current.
Thermocouples
Heat energy can be changed to electrical energy. When two different kinds of wire, such as iron and copper, are connected to form a loop, a current can be produced by heating the wires at one junction and cooling them at another. Such devices are called thermocouples, and they are used as thermostats on car engines. By placing one junction inside the engine and the other junction on the outside, a temperature difference is created when the engine becomes hot, and a small electrical current is generated. The hotter the engine becomes, the more current is generated. This current operates the temperature gauge on the car's dash.
Alternating Current
AC, or alternating current, changes direction 60 times per second. This type of electricity is produced by power plants and runs into our homes on long transmission wires. Most homes, businesses, and industries rely on alternating current.
Circuits
A circuit is the path along which electrons flow. The parts of a circuit include the source of electrons (e.g., battery, power plant), the load (e.g., light, radio), the wires, and a switch. The switch opens and closes the circuit.
In order for electricity to flow, the electrons need a closed path to follow. In other words, electrons can only travel along a circuit that begins at a negative pole and ends at a positive pole. In Figure A, both wires are connected to the battery, and electrons can flow along the path of the wire and operate the stereo headset, which represents the load. However, when one wire is not connected to the battery, as in Figure B, the circuit is incomplete and electrons will not move. Removing one wire from the battery has the same effect as opening a switch.
There are two types of circuits, depending on how the parts are connected. In a series circuit (see Figure C), there is only one path for electrons to follow. If there is a break anywhere in the circuit, current cannot pass along the circuit. Christmas tree lights are commonly wired in series, and if one light bulb is defective, none of the lights in the string will work. Household light circuits, however, are wired in parallel (see Figure D). If the bulb in one lamp burns out, other lights on that same circuit continue to burn.
Electrical Power
Every month, most people receive an electric power bill. We must pay for the electricity we use in our homes and businesses to perform work. Electric power is a measure of the rate at which electricity does work or provides energy. Electric power can be calculated by multiplying voltage used by the amount of current:
Power = voltage X current
P = v X I
Power is expressed in watts (W) and kilowatts (kW). A kilowatt is 1000 watts and is used to measure large amounts of power.
To determine how many watts of power are used by a light bulb on a 120-volt circuit with 0.5 amps of current, multiply voltage by amps:
P = v X I
P = 120 volts X 0.5 amps
P = 60 watts
Different appliances have different power ratings. The higher the rating, the greater the amount of electricity needed to run the appliance. Some common appliances and the power (watts) they use are as follows:
| Clock | 3 watts |
| Radio | 100 watts |
| Hair dryer | 1000 watts |
| Dishwasher | 2300 watts |
| Clothes dryer | 4000 watts |
Our electric power bills are based on the total amount of energy a household uses. This amount depends on the total amount used by all appliances multiplied by the time they were used.
Energy = power X time
E = P X t
Electric energy is expressed in kilowatt-hours (kWh). One kWh equals 1000 watts used for 1 hour. To get an idea of how much energy 1 kWh represents, imagine ten 100-watt light bulbs burning for 1 hour. Or think about the power used to operate a 500-watt TV for 2 hours.
The Cost of Electricity
When we pay our electric bill, we multiply the amount of energy used in kilowatt-hours by the cost of energy per kilowatt-hour. An average household might use 1000 kWh in a month. If the local utility company charges $ 0.7/kWh, multiply 1000 kWh by $ 0.7/kWh to determine the family's power bill:1000 kWh X $ 0.07/kWh = $70.00
