What determines the current in an electric circuit? - OCR 21st CenturyCurrent, potential difference and resistance
Electrical current depends on resistance and potential difference. Different electrical components have different characteristics. These can be investigated using suitable circuits and apparatus.
The currentMoving electric charges, eg electrons moving through a metal wire. in a circuit depends on the 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. and the resistanceThe opposition in an electrical component to the movement of electrical charge through it. Resistance is measured in ohms.. It is easy to think of each of these in the following way:
the current is the flow of electric chargeElectrical charge can be positive or negative. Like charges (+ and + or - and -) repel but unlike charges (+ and -) attract each other.
the potential difference provides the 'push'
the resistance restricts the flow of charges
Learn more on current, resistance and potential difference in this podcast
Electric wires are made of metal, which have electrical resistance. The atoms in a solid metal are arranged in a regular latticeA regular grid-like arrangement of atoms in a material. structure. The outer electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. from each atom are free to move through the structure, forming a current. However, they may collide with atoms or meet defects in the lattice. This reduces the number of electrons flowing, which reduces the current.
conductorAn electrical conductor is a material which allows an electrical current to pass through it easily. It has a low resistance. have a low resistance and insulatorMaterial that is a poor conductor of electricity or heat. have a high resistance.
Calculating potential difference
When a charge moves through a potential difference, electrical workEnergy transferred by a force. Work done = force × distance moved in the direction of the force. is done and energy is transferred. Potential difference can be calculated using the equation:
potential difference = current × resistance
This is when:
potential difference is measured in volts (V)
current is measured in amps (A)
resistance is measured in ohms (Ω)
Example
There is a current of 2.0 A in a component with a resistance of 40 Ω. Calculate the potential difference across the component.
potential difference = current × resistance
= 2.0 × 40
= 80 V
Question
There is a current of 2.0 A in a component with a potential difference of 12 V across the component. Calculate the resistance of the component.
Rearrange the equation to find resistance and then substitute in the known values.
