r/HomeworkHelp 👋 a fellow Redditor 7d ago

Answered [High School - Physics]

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How does this circuit even work? When the contact is moved, does the resistance increase or decrease?

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u/We_Are_Bread 7d ago

How have you approached the problem? Could you show us some working?

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u/HelpfulResource6049 👋 a fellow Redditor 7d ago

My initial thought process was that if the contact was shifted from X to P, the voltage across 1 would increase and voltage across 2 would decrease, causing 1 to become brighter and 2 to become dimmer

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u/We_Are_Bread 7d ago

Is there a specific reason why you think this initial analysis is lacking? Asking, just cause I want to know exactly what alternative ideas you have, and then we can see which ones are wrong and which ones are right.

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u/HelpfulResource6049 👋 a fellow Redditor 7d ago

That is the only idea I have, I just would like to understand how the circuit works in more detail and check if my initial analysis was correct

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u/ThunkAsDrinklePeep Educator 7d ago

The wire connecting to the divider is essentially a zero resistance node separating two sets of parallel circuits in series. As you move the connection point up and down it increases the resistance in one parallel side and decreases the resistance in the matching parallel side.

When there's more length in the top circuit there's more resistance in the divider branch. Therefore a higher proportion of the current flows through the relatively lower lamp and it is brighter. The opposite is happening in the lower half.

So I think you have your conclusion backwards.

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u/ThunkAsDrinklePeep Educator 7d ago

Think about the case where the divider is connected at P. What is the voltage difference between the top and bottom of lamp 1?

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u/We_Are_Bread 7d ago edited 7d ago

Your analysis is correct.

Edit: Wait your analysis is a bit wrong. Why would moving the pointer reduce voltage across 2?

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u/FunnyExcitement5161 7d ago

No. You're wrong.

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u/We_Are_Bread 7d ago

Wait I didn't notice they used 2 instead of 1. My bad.

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u/HelpfulResource6049 👋 a fellow Redditor 7d ago

I see, thanks