Using voltmeter only!
In the circuit above, when the switch is in position 0 , the voltmeter shows a voltage of . When the switch is in position 1 , the voltmeter shows a voltage of . What is the voltage (in volts) on the voltmeter when the switch is in position 2 ? Submit your answer to the nearest integer.
Details and Assumptions:
- The voltmeter is ideal, i.e. its internal resistance is infinitely large.
- The values of are unknown.
The answer is 8.
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1 solution
Here's the equivalent circuit for position 0:
We know that the voltage across the resistor is 6 in this case, which means that the product of the source current and the resistance must equal 6.
I R = 6
Here's the equivalent circuit for position 1:
Notice that the voltage source is applied directly across the resistance. Since we are told that the voltage measured across the resistance in this case is 12, we know that the voltage source value is 12.
E = 1 2
Here's the equivalent circuit for position 2. I have transformed the current source and parallel resistance into a Thevenin equivalent.
We see that the total voltage in the circuit is 24, and the voltmeter measures across one third of the total resistance. Therefore, the voltmeter measures 8 volts in this case.