Issue finding change in voltage across a resistor

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SUMMARY

The discussion focuses on calculating the voltage drop across resistor R1 in a circuit with resistors R1 = 770Ω, R2 = 630Ω, and R3 = 470Ω, resulting in an equivalent resistance of 816Ω. The user initially calculated the current using Ohm's Law (I = V/R) and found a current of 0.015A. However, the voltage drop across R1 was incorrectly calculated as 11.32V, leading to confusion regarding the distribution of current in the circuit. The correct approach involves recognizing that not all current flows through R1, necessitating a reevaluation of the circuit layout.

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  • Understanding of Ohm's Law (V = IR)
  • Basic knowledge of series and parallel resistor configurations
  • Ability to calculate equivalent resistance in circuits
  • Familiarity with circuit diagram representation
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Homework Statement



Determine the voltage drop across R1
R1 = 770 , R2 = 630 , and R3 = 470 .
The equivalent resistance is 816Ω

19-39alt.gif

Homework Equations



V = IR

The Attempt at a Solution



1.) I find the total current of the circuit:

V = IR -> I = V/R
I = 12v/816Ω = 0.015A

2.) I then find the voltage drop across that particular resistor:

V = IR
V = 0.015A * 770Ω
V = 11.32v

This has been confirmed to be the wrong answer.

I don't understand what I am doing incorrectly.

Could someone please help me understand my mistake (where ever it may be)?

Many Thanks!
 
Physics news on Phys.org
You need to draw the circuit with all of the voltages and currents labeled so that you can see clearly what is going on. Thinking that the 15ma all goes through R1 is incorrect.
 

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