Download G2 Chemical Patterns – revision checklist

GE6: Modelling the behaviour of Electric Circuits
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Ge6.1
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Ge6.2
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Where are the charges in circuits and how can they be made to move?
appreciate that electric current is a flow of charge;
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explain that in an electric circuit the components and wires are full of
electrons that are free to move;
explain that when a circuit is made the battery causes
these free electrons to move, and that they are not used
up but flow in a continuous loop
recall that in metallic conductors an electric current is a
movement of free negatively charged electrons
What determines the size of the current in an electric
circuit?
explain that the larger the voltage of the battery, the
bigger the current.
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recognise that components (such as resistors, bulbs, motors) resist
charge flowing through them;
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relate the resistance of the components, to the current
through them;
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appreciate that the resistance of connecting wires is so small that it
can usually be ignored;
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recall that resistors are heated when electric current
passes through them;
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describe how a bulb filament gets hot enough to glow, and
that this heating effect is caused by collisions between
the moving charges and stationary atoms in the wire.
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Ge6.3
explain that two (or more) resistors or lamps in series have more
resistance than one on its own because the battery has to push
charges through both of them;
explain that two (or more) resistors in parallel provide
more paths for charges to flow along than one resistor on
its own so the total resistance is less, and the current is
bigger.
How do parallel and series circuits work?
What is voltage?
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recognize that potential difference is another term for voltage;
relate the potential difference (voltage) between two points in the
circuit to the energy transferred to, or from, a given amount of
charge as it passes between these points;
describe the effect on voltage and current of adding
further batteries in series and in parallel with original
one.
How does potential difference (voltage) behave in a series circuit?
appreciate that when several components are connected in series to a
battery:
 the current through each component is the same;

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the potential differences across the components add up to
the potential difference across the battery (because the
total energy transferred to each unit of charge by the
battery must equal the amount transferred from it to
other components);
explain that the potential differences across the
components are in direct proportion to their resistance
values, because more energy is transferred by the
charge passing through a large resistance than through
a small one.
How does current behave in a parallel circuit?
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Candidates should be able to apply these ideas to describe and
explain simple features of domestic mains electric circuits in
particular safety devices, fuses, earth and RCDs (all devices at same
operating voltage, each independently switched).
appreciate that when several components are connected in parallel
directly to a battery:
 the potential difference (voltage) across each component is
equal to the voltage of the battery;
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Ge6.4
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the current through each component is the same as if it
were the only component present;
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the total current from (and back to) the battery is the sum
of the currents through each of the parallel components.
How is mains electricity produced?
How are voltages and currents induced?
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recall that mains electricity is produced by generators;
recall that generators produce a voltage by a process called induction;
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recall that when a magnet is moving into a coil of wire a
voltage is induced
across the ends of the coil;
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recognise that if the ends of the coil are connected to make a closed
circuit, a current will flow round the circuit;
recall that if the magnet is moving out of the coil, or the
other pole of the magnet is moving into it, there is a
voltage induced in the opposite direction.
describe how in a generator, a coil of wire is rotated in a magnetic
field (or a magnet is rotated within a coil of wire) to induce a voltage
across the ends of the coil;
understand that the size of this induced voltage can be increased by:
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increasing the speed of rotation of the coil (or the magnet);
increasing the strength of the magnetic field;
increasing the number of turns on the coil;
placing an iron core inside the coil.
explain, when provided with an appropriate diagram, why a
generator has brushes and slip rings, and how these work.
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How is mains electricity generated?
describe how the induced voltage across the coil of a
generator changes during each revolution of the coil
and explain that the current produced in an external
circuit is an alternating current (a.c.);
appreciate that the current from a battery always travels in the same
direction: it is a direct current (d.c.);
recall that mains electricity is an a.c. supply;
appreciate that a.c. is used because it is easier to generate, and
can be distributed more efficiently, than d.c;
recognise that the mains supply voltage to our homes is 230 volts.
note
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Ge6.5
How much electrical energy do we use at home?
Candidates will not need to recall any details of d.c. generators.
Details of transmitting power at high voltage are not required.
How do voltage and current affect electrical energy?
use the following equation to calculate energy transfer in joules and
kilowatt-hours:
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energy transferred = power
×
(joules, J)
(watts, W)
(kilowatt hours, kWh) (kilowatts, kW)
time
(seconds, s)
(hours, h)
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Transformation of these equations is only required on the
higher tier.
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appreciate that when electric charge flows through a component (or
device), energy is transferred to the component;
state and be able to use the equation:
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power
=
(watts, W)
potential difference (voltage) × current
(volts, V)
(amperes, A)
How much does my electricity cost?
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explain that a joule is a very small amount of energy, so a domestic
electricity meter measures the energy transfer in kilowatt hours;
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calculate the cost of electrical energy given the power, the time and
the cost per kilowatt hour;
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state and be able to use the equation in the context of different
electrical appliances:
efficiency =
energy usefully transferred
total energy supplied