Page 95 - Physics_Form_2

Current electricity
Chapter summary
1. Electromotive force (e.m.f), is
the maximum potential difference
between two terminals of a battery or
a cell when no current is drawn from
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the battery or cell. In other words, it
is the electrical intensity or pressure
developed by a source of electrical
energy.
2. Electric potential difference (p.d)
is the work done per unit charge in
moving the electric charge from one
point to another point of a conductor.
3. Electric current, I, is defined as the
rate at which electric charge, Q,
passes a given point by a unit of
the ampere, A, and is measured by
an instrument called an ammeter.
4. Resistance is the opposition to
the flow of electric current in a
conductor. It is measured in ohms
(Ω).
5. The resistance of a conductor is
affected by: temperature, its length,
cross-sectional area and material of
the conductor.
6. When resistors are connected in
series, the total resistance in the
circuit is equal to the sum of the
individual resistances.
7. When resistors are connected in
parallel, the reciprocal of the total
resistance is equal to the sum of
the reciprocals of the individual
resistances.
8. When an electric current flow through
a conductor of high resistance, the
Physics Form 2 Final.indd 89
electrical energy gets converted
into thermal energy and heats the
conductor. This is known as the
heating effect of an electric current.
9. Every electrical appliance should
carry a label stating the potential
difference for which it has been
designed and the power it can
convert when operating at the stated
potential difference.
10. Electricity is supplied in consumers’
places by low-resistance wire made
up of either copper or aluminium
material insulated with plastic.
11. The wires used in electrical
installation are rated according to
the maximum current they can carry.
12. Domestic electricity is supplied
by two cables; the live cable (L),
coloured brown or red, and the
neutral cable (N) usually coloured
blue or black.
13. The rate at which an appliance
dissipates energy is called the rating
of that appliance and is usually
marked on the body of the appliance.
14. There are two common types of
electrochemical cells, namely
primary and secondary cells.
15. The total voltage across cells
connected in series is equal to the
sum of the voltages of the individual
cells while in parallel connection,
the effective voltage is equal to
the voltage of one of the cells (for
identical cells).
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