Finding an open-cicuit voltage, why is resistor in series ignored?

  • #1
justin___
2
2
Homework Statement
The circuit you should use to find the open-circuit voltage, voc, is shown here. Note that the resistor to the right of terminals a and b has been removed to create the open circuit. Using any circuit analysis technique you like, find the open-circuit voltage.
Relevant Equations
KCL
I found how to get the solution to this question (the answer is 200V), but I don't understand why we ignore the 30kOhm resistor when using analysing the circuit. Because it is in series with the open voltage, wouldn't there be some voltage drop across the resistor that would affect the open-circuit voltage?

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Thanks
 
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  • #2
Hint:
Can you write the equation for the voltage drop across a resistor given its value and the current thru it?

Upon inspection of that equation, the light bulb above your head will likely come on.

Cheers,
Tom
 
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  • #3
Tom.G said:
Hint:
Can you write the equation for the voltage drop across a resistor given its value and the current thru it?

Upon inspection of that equation, the light bulb above your head will likely come on.

Cheers,
Tom
Thanks for the hint. So because the 30kOhm resistor is in series with an open circuit, no current flows through it, therefore there is no voltage drop and we can ignore it from the equation?
 
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1. What is an open-circuit voltage?

An open-circuit voltage is the voltage across a circuit when there is no current flowing through it. It is measured by connecting a voltmeter across the two open ends of the circuit.

2. Why is the resistor in series ignored when finding an open-circuit voltage?

The resistor in series is ignored because it does not affect the voltage in an open circuit. In an open circuit, there is no current flowing, so there is no voltage drop across the resistor. Therefore, the resistor can be considered as having no effect on the open-circuit voltage.

3. Can the open-circuit voltage be measured with a multimeter?

Yes, a multimeter can be used to measure the open-circuit voltage. Set the multimeter to the voltage measurement mode and connect the probes across the open ends of the circuit. The reading on the multimeter will be the open-circuit voltage.

4. What is the significance of finding the open-circuit voltage?

The open-circuit voltage is an important parameter in circuit analysis as it helps determine the behavior of the circuit. It can be used to calculate the Thevenin equivalent voltage and resistance, which are useful in simplifying complex circuits.

5. How does the open-circuit voltage differ from the short-circuit current?

The open-circuit voltage is the voltage when there is no current flowing through the circuit, while the short-circuit current is the current when there is no voltage drop across the circuit. In other words, the open-circuit voltage is the maximum voltage that a circuit can provide, while the short-circuit current is the maximum current that can flow through the circuit.

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