Total
Equivalent Resistance RT of the Circuit
The total equivalent resistance
RT
of the circuit is found by adding up the
resistance values of the individual resistors.
Consider
the series combination of the five resistances
in Figure 9.1. The same current has to pass
through all the resistances in the loop.
An ammeter placed anywhere in the circuit
would measure the same amount.
The total voltage across a series circuit
that consists of more than one resistor
is also equal to the applied voltage, but
consists of the sum of the individual resistor
voltages. The voltage across each resistor
is known as voltage drop.
It is similar to the pressure drop in a
water system. The voltage drop across each
resistor in a series circuit is proportional
to the ohmic value of the resistor. In any
series circuit, the sum of the resistor
voltage drops must be equal to the source
voltage. By Ohm’s law, we may write
and
then
Experimentally, the voltage
drops in a series circuit can be measured
by connecting a voltmeter across each resistor
as shown in Figure 9.2.
Figure 9.2 The voltage
drops in a series circuit.
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