Basic Concepts:
Electric voltage is a physical quantity corresponding to the difference of the electric potential between two points and it represents the energy necessary to transfer the electric charge between these two points in a certain electric field. The unit of voltage is the volt (V). Transformer is used to change the voltage from high to medium or vice versa. This works on a principle of two coils with a different number of turns. When the voltage passes from the coil with a higher number of turns to the coil with a lower number of turns, the voltage decreases and vice versa, when the voltage passes from the coil with a lower number of turns to the coil with a higher number of turns, the voltage increases.
The unit of electric current is the Ampere (A). If the current flows only in one direction it is called direct current. An example is the current in a battery powered circuit which flows from the negative pole to the positive pole. If the current changes its direction, it is called alternating current. This occurs when the rotary magnetic field changes its direction. If the change occurs 50 times per second, it is has a frequency of 50 Hertz. Voltage transformation is easier with the alternating current.
Output is the product of voltage and current. It is comparable to the power developed when water is squirting from a hose with a certain flow and pressure. The unit of output is the watt (W), however, kilowatt (kW) is used more frequently.
Resistance depends on the kind and diameter of the metal which enables the current to flow through the circuit. The unit of resistance is the ohm (Ω).
Consumption means the volume of electricity used within a time period and it is measured in kilowatt hours (kWh).
For example, 1 kWh equals to the work performed by a 75 kg tourist when climbing on Mont Blanc (4 810 m above sea level.). What can we do with 1 kWh?
- have 20 W energy efficient fluorescent light bulb lit for 50 hours
- heat 17 l of water to 60 °C
- wash 5 kg of dry laundry at the temperature of 60 °C or 3 kg of laundry with pre-washing
- refrigerate food for 24 hours in a 300 l refrigerator or freeze it in a 230 l drawer freezer
- cook lunch for 4 persons
- iron for 1.5 hours
- vacuum clean a 4-room apartment 4 times
- wash dishes in a dishwasher (1 cycle)
- listen to CD walkman for 40 hours
- use a computer with color monitor for 4 – 6 hours
