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electricity
series and parallel
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Cards (7)
The electrical power is also defined as the
rate of change of work done
:
The work done is the
energy transferred
The power is, therefore, the
energy transferred per second
in an electrical component
Rearranging the energy and power equation, the energy can be written as:
W
=
Pt
= IVt
The power of an appliance is:
The amount of energy transferred (by
electrical work
) to the
device every second
A kilowatt-
hour
is defined as:
A unit of
energy
equal to 1
kW
of power sustained for 1 hour
Or as an equation:
Energy
(kW h) = Power (
kW
) × Time (h)
Since
the
usual unit of energy is
joules
(J), this is the 1 W in 1 s
Therefore:
1
kW h =
1000
W × 3600 s = 3.6 × 106 J
Since 1 kW =
1000
W and 1 h = 3600 s
To convert between Joules and kW h:
kW h × (3.6 ×
106
) = J
J ÷ (3.6 ×
106
) = kW h
Kirchhoff’s second law states that:
The sum of the e.m.f’s in a
closed circuit
equals the sum of the
potential differences
In a series circuit, the voltage is split across all components depending on their resistance
The sum of the voltages is equal to the
total e.m.f
of the
power supply
In a parallel circuit, the voltage is the
same
across each
closed loop
The sum of the voltages in each closed circuit loop is equal to the
total e.m.f
of the
power supply
:
The
total voltage
of the combined cells can be calculated in the
same
way as voltage
If the cells are connected in series, the
total voltage
between the ends of the chain of cells is the sum of the
potential difference
across each cell
If the cells are connected in parallel, the
total voltage
across the arrangement is the
same
as for one cell