Voltage and ResistanceThe amount of current (in amps) flowing through a circuit will partly depend on electromotive force (EMF) of the electrical supply. Electromotive force is measured in volts (V), and is generally called voltage. The voltage depends on the ‘strength’ of the electrical supply. The electric current flows only when there is a potential difference between the two points in the circuit. The opposition to the current flow is the resistance. Thus we can say that the current is directly proportional to the voltage and inversely proportional to the resistance (Ohm’s law): I=U/R. Thus, the amount of current will also depend on electrical resistance (or resistance). Resistance is a measure of how easily current can flow through the conductors and components in a circuit. For example, a lamp creates resistance because the filament (the metal wire inside it) is very thin. This limits the amount of current that can flow. Resistance also depends on the materials used as conductors (a material or device that conducts or transmits electricity). For example, copper has a low resistance and so is a good conductor. Materials with very high resistance, such as plastics, are called electrical insulators (or insulators). Only very high voltages can cause current to flow through them. Materials that are good insulators are used to insulate conductors. An example is plastic insulation around electric wires. This stops people from touching the conductor and – if it is live (carrying current) – from getting a dangerous electric shock.
|
