This circuit consists of resistors in parallel and in series, an arrangement we have looked
at before. Following the same two steps as we did last time, we can calculate the total
resistance in the circuit:
- Determine the equivalent resistance of the resistors in parallel.
We can conclude that = 4.
- Treating the equivalent resistance of the resistors in parallel as a
single resistor, calculate the total resistance by adding resistors in
series.
Given that the total resistance is 9 and the total voltage is 9 V, Ohm’s Law tells us that
the total current is:
The ammeter will read 1 A.
WHAT DOES THE VOLTMETER READ?
The voltmeter is connected in parallel with and , so it will register the voltage drop
across these two resistors. Recall that the voltage drop across resistors in parallel is the
same for each resistor.
We know that the total voltage drop across the circuit is 9 V. Some of this voltage drop
will take place across , and the rest of the voltage drop will take place across the
resistors in parallel. By calculating the voltage drop across and subtracting from 9 V,
we will have the voltage drop across the resistors in parallel, which is what the voltmeter
measures.
If the voltage drop across is 5 V, then the voltage drop across the resistors in parallel is
9 V – 5 V = 4 V. This is what the voltmeter reads.