Section 5: Electricity Flashcards
Define current
The rate of flow of charge.
(Coulombs per unit time)
Define potential difference
The energy transferred between two points in a circuit per unit charge.
(Joules per coulomb)
Define resistance
A measure of how difficult it is for charge carriers to pass through a component.
Define Ohm’s law
For an ohmic conductor, current is directly proportional to the potential difference across it, provided the physical conditions are kept constant.
Define resistivity
A measure of how easily a material conducts electricity. Resistivity will give the value of resistance through a material of length 1 metre and cross-sectional area 1m^2
How does a thermistor function?
As its temperature increases, its resistance decreases.
This is because as the temperature increases, electrons are emitted from atoms, increasing the number of charge carriers, and current increases, thereby decreasing the resistance.
Define a superconductor
A material which, below a certain temperature (known as the critical temperature), has zero resistivity.
Describe two uses of superconductors
Power cables, to reduce energy loss through heating to zero.
Strong magnetic fields, such as the ones used for maglev trains and certain medical applications.
Describe current in a series vs a parallel circuit
In a series circuit, the current in the same everywhere in the circuit.
In a parallel circuit, the current is split across the branches, and the sum of the currents in the parallel branches equals the total current.
Describe potential difference in a series vs a parallel circuit
In a series circuit, the supply potential difference is shared across all elements in the circuit, and the sum of the voltages across all elements equals the supply potential difference.
In a parallel circuit, the potential difference across each branch is the same. Each separate loop behaves like a series circuit, in that the supply potential difference is split across all the components.
Describe how the supply potential difference varies when multiple cells are connected in series vs in parallel
In series, the total voltage is the sum of the individual voltages of the cells.
In parallel, as long as the cells are identical, the voltage will be equal to that of one cell. If the cells are non-identical, the lowest voltage will be the total voltage.
