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Introduction to SAT II Physics - FreeExamPapers

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This circuit consists of resis<strong>to</strong>rs in parallel and in series, an arrangement we have looked<br />

at before. Following the same two steps as we did last time, we can calculate the <strong>to</strong>tal<br />

resistance in the circuit:<br />

1. Determine the equivalent resistance of the resis<strong>to</strong>rs in parallel.<br />

We can conclude that = 4 .<br />

1. Treating the equivalent resistance of the resis<strong>to</strong>rs in parallel as a<br />

single resis<strong>to</strong>r, calculate the <strong>to</strong>tal resistance by adding resis<strong>to</strong>rs in<br />

series.<br />

Given that the <strong>to</strong>tal resistance is 9<br />

the <strong>to</strong>tal current is:<br />

and the <strong>to</strong>tal voltage is 9 V, Ohm’s Law tells us that<br />

The ammeter will read 1 A.<br />

WHAT DOES THE VOLTMETER READ?<br />

The voltmeter is connected in parallel with and , so it will register the voltage drop<br />

across these two resis<strong>to</strong>rs. Recall that the voltage drop across resis<strong>to</strong>rs in parallel is the<br />

same for each resis<strong>to</strong>r.<br />

We know that the <strong>to</strong>tal voltage drop across the circuit is 9 V. Some of this voltage drop<br />

will take place across<br />

, and the rest of the voltage drop will take place across the<br />

resis<strong>to</strong>rs in parallel. By calculating the voltage drop across and subtracting from 9 V,<br />

we will have the voltage drop across the resis<strong>to</strong>rs in parallel, which is what the voltmeter<br />

measures.<br />

If the voltage drop across<br />

is 5 V, then the voltage drop across the resis<strong>to</strong>rs in parallel is<br />

9 V – 5 V = 4 V. This is what the voltmeter reads.<br />

Fuses<br />

231

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