LDR circuit electricity question

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Homework Help Overview

The discussion revolves around an LDR (Light Dependent Resistor) circuit, specifically focusing on the arrangement of resistors and the behavior of voltage across them. Participants are exploring the configuration of resistors in parallel and the implications for voltage readings.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to clarify the arrangement of resistors R1, R2, and R3, questioning whether their configurations are correctly understood. They also inquire about achieving a specific voltage reading and the conditions under which resistances might "cancel" each other out.

Discussion Status

Some participants have provided references to external resources related to bridge circuits, suggesting avenues for further exploration. The conversation indicates that multiple interpretations of the circuit's behavior are being considered, but there is no explicit consensus on the next steps.

Contextual Notes

Participants are discussing the implications of resistor configurations and voltage readings without full clarity on the circuit's setup or the specific goals of the analysis. There may be assumptions about the circuit's behavior that are yet to be fully addressed.

Zeynaz
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Homework Statement
Switch S is closed and light falls on the LDR. The variable resistor R3 is set such that the voltmeter reads 0V. The resistance of R3 then is 720 ohms.

a) show that the resistance of the LDR is 720 ohms.
Relevant Equations
V=IR
242084

So far what i figured out is that R2 and R3 are in parallel, R1 and LDR in parallel. And these two parallel circuits are parallel to each other ( tell me if I am wrong)

The voltmeter has to read 0 but I am not sure how i can achieve that. Is there a rule where when the resistance of each side is equal they cancel each other?

For the lower parallel half i found the total R by using resistance for parallel circuits. This gives me R-lower=300 ohms.

Also voltage of R3 and R2 has to be equal to each other because they are in parallel.

So how should I proceed?
 
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If do a search for Bridge Circuit, you can find several resources. Here is one that goes through the method. https://courses.engr.illinois.edu/ece110/sp2019/content/courseNotes/files/?nodeMethod
 
Alright! thanks
 
You may see it called Wheatstone Bridge.
 
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