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By reference to heating effect, explain what is meant by the root-mean-square (r.m.s.) value of an alternating current.
The variations with time 
of two currents 
and 
are shown in graph I and graph II below.
Use graph I to determine the peak value and the r.m.s. value of the current .
Use graph II to determine the peak value and the r.m.s. value of the current .
The variation with time of the supply voltage 
to a house is given by the expression
where is in volts, is in seconds and 
is a constant with unit 
.
The frequency of the supply voltage is 
. Determine to two significant figures.
The supply voltage is applied to a heater. The mean power of the heater is 
. Calculate the resistance of the heater.
.
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