1.1 When certain insulating materials are rubbed
against each other they become electrically
charged. Negatively charged electrons are
rubbed off one material and onto the other.
1.1.1 The material that gains electrons becomes
negatively charged. The material that loses
electrons is left with an equal positive charge.
1.1.1.1 When two electrically charged objects are brought together they exert a force on each other.
1.1.1.1.1 Two objects that carry the same type
of charge repel. Two objects that carry
different types of charge attract.
1.1.1.1.1.1 Electrical charges can move
easily through some
substances, for example metals.
2 P2.3.2 Electrical Circuits
2.1 Electric current is a flow of electric
charge. The size of the electric current is
the rate of flow of electric charge. The size
of the current is given by the equation:
I=Q/t where I is the current in amperes
(amps), A, Q is the charge in coulombs, C
and t is the time in seconds, s.
2.1.1 The potential difference (voltage) between
two points in an electric circuit is the work
done (energy transferred) per coulomb of
charge that passes between the points.
V=W/Q where V is the potential difference
in volts, V, W is the work done in joules, J
and Q is the charge in coulombs, C.
2.1.1.1 Current–potential difference graphs are used to show how the current
through a component varies with the potential difference across it.
2.1.1.1.1 The resistance of a component can be found
by measuring the current through, and
potential difference across, the component.
The current through a resistor (at a constant
temperature) is directly proportional to the
potential difference across the resistor.
2.1.1.1.1.1 V=I×R where V is the potential difference in
volts, V, I is the current in amperes (amps),
A and R is the resistance in ohms, Ω.
2.1.1.1.1.1.1 The current through a component depends
on its resistance. The greater the resistance
the smaller the current for a given potential
difference across the component.
2.1.1.1.1.1.1.1 The potential difference provided by cells
connected in series is the sum of the
potential difference of each cell (depending
on the direction in which they are connected).
2.1.1.1.1.1.1.1.1 For components connected in
series the total resistance is the sum
of the resistance of each component,
there is the same current through
each component and the total
potential difference of the supply is
shared between the components.
2.1.1.1.1.1.1.1.1.1 For components connected in parallel the potential
difference across each component is the same and
the total current through the whole circuit is the sum
of the currents through the separate components.
2.1.1.1.1.1.1.1.1.1.1 The resistance of a
filament bulb increases as
the temperature of the
filament increases.
2.1.1.1.1.1.1.1.1.1.1.1 The current through a diode flows in one direction only. The diode
has a very high resistance in the reverse direction.
2.1.1.1.1.1.1.1.1.1.1.1.1 An LED emits light when a current flows
through it in the forward direction.
2.1.1.1.1.1.1.1.1.1.1.1.1.1 The resistance of a light-dependent
resistor (LDR) decreases as light intensity
increases. The resistance of a thermistor
decreases as the temperature increases.