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Slide 1

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Current Electricity
A circuit diagram uses the symbols A battery consists of two
to show how components are or more cells.
connected together to make a
circuit.
A cell is necessary to push electrons around a
complete circuit. A battery consists of two or
more cells.
A switch enables the current in a circuit to be
switched on or off.
An indicator is designed to emit light as a
signal when a current passes through it or as a
light source such as a lamp.
A diode allows current through in one direction
only.
An ammeter is used to measure electric
current.
A fixed resistor limits the current in a circuit.
A variable resistor allows the current to be
varied.
A fuse is designed to melt and therefore
`break' the circuit if the current through it is
greater than a certain amount.
A heater is designed to transform electrical
energy to heat.
A voltmeter is used to measure potential
difference (voltage)…read more

Slide 2

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Current is measured by an The potential difference is
ammeter (A) and is placed measured with a voltmeter (v) and
in series with the placed in parallel with the
component. component.
If the resistor is kept at a constant temperature the graph
shows a straight line passing through the origin. This means
the currents is directly proportional to the potential
difference across the resistor.
In a filament lamp, resistance increases
with increase of filament temperature.
In a diode, `forward' resistance is low
`reverse' resistance is high.
In a thermistor resistance
decreases if its temperature
increases.
In a LDR resistance decreases if the
light intensity on it increases.
For components in a series:
The current is the same in
each component
The potential differences add
to give the total potential
The resistances add to give Diode Filament
the total resistance Lamp
Current= p.d of supply For components in parallel:
total resistance The potential difference is the same
Potential difference = across each component
current x resistance The total current is the sum of the
currents through each component
The bigger the resistance of a
component the smaller its current is.
Resistance (ohms ) = potential difference (volts V)
current (amperes A)…read more

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