current flow consisting of charges that continually change direction
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ammeter
a device connected in series with a component to measure the current that flows through it
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amp ( A )
unit of current
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Circuit breaker
A safety device that cuts off the power supply if a surge of current passes through it
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coulomb
unit of charge
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currents at a junction
the sum of current entering a junction must always equal the sum of currents leaving it
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diode
a component that only allows current to flow in the forward direction
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direct current
current flow consisting of charges flowing in a single direction only
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earth wire
the green and yellow striped safety wire connected to metal casings that prevents an appliance from becoming live
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electric current
the rate of flow of charge
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energy transfers in circuits
electrical energy is transferred to thermal energy when current does work against a resistance
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filament lamp
a light emitting component consisting of an enclosed metal filament
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fuse
a safety device consisting of a thin metal filament that melts and cuts off a power supply if there is a surge in current
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Light Dependent Resistor
A light sensitive component whose resistance decreases as its temperature increases
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Light emitting diode
a device that gives out light when a current flows through it. Current can only flow in one direction and a minimum voltage must be applied across it before it lights up
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live wire
the brown coloured wire that carries the alternating current from the supply in a mains power supply
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mains electricity
An a.c supply that, in the UK, has a frequency of 50 Hz and a value of 230V
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Neutral Wire
the blue coloured wire that completes the circuit in a mains power supply
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Ohmic Conductor
A conductor whose current flow is directly proportional to the potential differance across it, when kept at a constant temperature
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Ohms
Unit of resistance
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Ohm’s law
the current flowing through an Ohmic conductor at a constant temperature is directly proportional to the potential differance across it
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Parallel
Components connected in parallel had the same voltage across each component an the total current is equal to the total sum of currents flowing through each component
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potential differance ( voltage )
the energy that is transferred per unit of charge between 2 points in a circuit
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power
the rate at which an appliance transfers energy
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power for a circuit component =
current passing through it x voltage across it
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resistance
a measure of the opposition to current flow
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resistors in parallel
the total resistance is less than the lowest individual resistance
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resistors in series
the total resistance is equal to the sum of the resistances of the individual resistors
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series
components connected in series have the same current passing through but share the total voltage of the power supply
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thermistor
a temperature dependent component, whose resistance increases as temperature decreases
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volt
the unit of potential differance
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1 volt =
1 joule / coulomb
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volt metre
a device that is connected in parallel with a component to measure the potential differance across it
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watt
the unit of power
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energy transferred =
charge moved x voltage
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charge =
current x time
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voltage =
current x resistance
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resistors heat up when used because …
… the electrons carrying the charge collide with the ions in a lattice in the resistor, increasing the kinetic energy, increasing the temperature
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