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electric circuit question

I understand why D is right and why BC is wrong. But why does the reading of the voltmeter when Switch is open equals to emf, should it not equal to 0?


In the circuit shown, V is a voltmeter with a very high resistance. The internal resistance of the cell,
r, is equal to the external resistance in the circuit.

Which of the following is not equal to the emf of the cell?

A the reading of the voltmeter when the Switch S is open
B the chemical energy changed to electrical energy when unit
charge passes through the cell
C twice the reading of the voltmeter when the switch S is
closed
D the electrical energy produced when unit current passes
through the cell

Diagram reference
https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FPhysics%2FA-level%2FTopic-Qs%2FAQA%2F05-Electricity%2FSet-M%2FCurrent%2520Electricity%2520(Multiple%2520Choice)%2520QP.pdf (Q10)
(edited 2 years ago)
The switch doesnt disconnect the Voltmeter from the cell, it does disconnect the rest of the circuit from the cell though so with the switch open you get the open circuits voltage of the cell... Which is also the EMF of the cell.
Original post by Joinedup
The switch doesnt disconnect the Voltmeter from the cell, it does disconnect the rest of the circuit from the cell though so with the switch open you get the open circuits voltage of the cell... Which is also the EMF of the cell.

I see. Thank you!
Reply 3
Original post by Joinedup
The switch doesnt disconnect the Voltmeter from the cell, it does disconnect the rest of the circuit from the cell though so with the switch open you get the open circuits voltage of the cell... Which is also the EMF of the cell.

Why are B and C not correct?
Original post by cata03
Why are B and C not correct?


you need to pick the one choice out of 4 that's not the EMF
Reply 5
Original post by Joinedup
you need to pick the one choice out of 4 that's not the EMF

Omg i’m so stupid thank you hahahah
Original post by anonymouss2004
I understand why D is right and why BC is wrong. But why does the reading of the voltmeter when Switch is open equals to emf, should it not equal to 0?
In the circuit shown, V is a voltmeter with a very high resistance. The internal resistance of the cell,
r, is equal to the external resistance in the circuit.
Which of the following is not equal to the emf of the cell?
A the reading of the voltmeter when the Switch S is open
B the chemical energy changed to electrical energy when unit
charge passes through the cell
C twice the reading of the voltmeter when the switch S is
closed
D the electrical energy produced when unit current passes
through the cell
Diagram reference
https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FPhysics%2FA-level%2FTopic-Qs%2FAQA%2F05-Electricity%2FSet-M%2FCurrent%2520Electricity%2520(Multiple%2520Choice)%2520QP.pdf (Q10)

Please see this video for better understanding this plroblem is solved completly on this video: https://youtu.be/4812hVk6Wyg

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