What determines the current in an electric circuit? - OCR 21st CenturyElectric current
Electrical current depends on resistance and potential difference. Different electrical components have different characteristics. These can be investigated using suitable circuits and apparatus.
currentMoving electric charges, eg electrons moving through a metal wire. is the rate of flow of chargeElectrical charge can be positive or negative. Like charges (+ and + or - and -) repel but unlike charges (+ and -) attract each other.. In metal wires, electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. move and cause a current. The following conditions are needed for an electric currentThe movement of electrically charged particles, for example, electrons moving through a wire or ions moving through a solution.:
a source of potential differenceThe potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them., such as a batteryA chemical supply of electrical energy. For example, common battery voltages include 1.5 V and 9 V., cell or power pack
a closed circuitA closed loop through which current moves - from a power source, through a series of components, and back into the power source., which provides a complete path for the charges to move through
Originally, current was defined as the flow of charge from positive to negative. Scientists later discovered that current is actually the flow of electrons, from negative to positive. The original definition is now referred to as 'conventional current', to avoid confusion with the newer definition of current.
Learn more on electrical charge and current in this podcast
Each electron in a circuit carries a very small charge but there are many billions of electrons present. Many everyday currents for small household appliances will be measured in milliamps, mA: 1,000 mA = 1 A.
Example calculation
A current of 60 mA passes through a lamp for half an hour. Calculate the charge transferred.
60 mA = 60 ÷ 1,000 = 0.060 A
0.5 hours = 30 minutes
= 30 × 60 = 1,800 s
charge flow = current × time
= 0.060 × 1,800
= 108 C
Question
A charge of 5.0 C is transferred through a wire in 20 s. Calculate the current in the wire.
