Basic electricity
Don't
forget to play with the computer model on the network and download your own copy onto your home computer (applies only to students at WGHS).
Summary of Basic
Circuit Knowledge
ammeter
cells
in series
characteristic
curves
circuit
symbols
current
diode
Kirchhoff's
First Law
parallel
circuits
potential
difference
resistances
in parallel
resistances
in series
series
circuits
strands of a circuit
voltmeter
An interactive PowerPoint presentation for you to use on the topic of resistance
A
current will flow through an
electrical component (or device) only if there is a voltage or potential
difference (p.d.) across its ends. The bigger the potential difference
across a component, the bigger the current that flows through it.
There must be a complete circuit for a current to flow. If there is a gap in the circuit then the whole strand that the gap is in will not have current flow through it.
Components resist a current
flowing through them. The bigger their resistance,
the smaller the current produced by a particular voltage, or the bigger
the voltage needed to produce a particular current.
The
p.d. across a component in a circuit is measured in volts (V) using
a voltmeter
connected across
(in parallel with) the component.
The current flowing through
a component in a circuit is measured in amperes (A) using an ammeter
connected
in series with the component.
When
components are connected in series:
. their total resistance
is the sum of their separate resistances
RTOTAL = R1 + R2 + ..........RN;
. the same current flows through
each component;
. the total potential difference
of the supply is shared between them.
When
components are connected in parallel:
. there is the same potential
difference across each component;
. the current through each component
depends on its resistance; the greater the resistance of the component,
the smaller the current;
. the total
current through the whole circuit is the sum of the currents through
the separate components - this follows from Kirchhoff's First
Law - see below.
The potential difference
provided by cells connected in series is the sum of the potential
difference of each cell separately (bearing in mind the direction
in which they are connected).
A
cell's potential difference between its terminals has a chemical source
and that this can 'run down' with use or incorrect storage
providing less of an electrical gradient for the current (i.e. the
voltage stamped on a battery might not be correct).
You
should be able to interpret and/or draw circuit diagrams using standard
symbols. The following standard symbols should be known:
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connecting
wire
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connection
between two crossing wires
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two crossing
wires that are not connected to each other
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switch
(open)
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switch
(closed)
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signal
lamp
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filament
lamp
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cell
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battery
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power supply
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fuse
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resistor
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diode
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variable
resistor
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thermistor
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ammeter
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voltmeter
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L.D.R.
(light dependant resistor)
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Potential difference, current
and resistance are related as shown:
V = I
R
Where: V = potential difference (in
volts, V)
I =
current (in ampere, A)
R = resistance (in ohm, W)
Current-voltage
graphs are used to show how the current through a component varies
with the voltage you put across it.
These are called Characteristic
Curves (Click here).
As an electric current flows through
a circuit, energy is transferred from the battery or power supply
to the components in the electrical circuit.
An electric current is a flow
of charge.
When electrical charge flows
through a resistor, electrical energy is transferred as heat.
The rate of energy transfer (power) is
given by:
P = IV
Where: P = power (in watts, W)
V = potential difference (in volts,
V)
I =
current (in ampere, A)
1 watt is the transfer of 1J
of energy in 1s.
The higher the voltage of a
supply, the greater the amount of energy transferred for a given amount
of charge which flows.
E = VQ
Where E = energy transferred (in joule,
J)
V = potential difference (in volt,
V)
Q = charge (coulomb, C)
The amount of electrical charge
which flows is related to current and
time as follows:
Q = I
t
Where: Q = charge (coulomb, C)
I =
current (in ampere, A)
t = time (in seconds, s)
The total amount of energy transferred by an electrical device can be calculated as follows:
E = Pt
Where E = energy transferred (in joule,
J)
P = power (in watts, W)
t = time (in seconds, s)
Using
Domestic Electrical Appliances click here