Solving a Bridge Circuit: Input Voltage, Resistances, and Output Voltage

  • Thread starter Thread starter ElBell
  • Start date Start date
  • Tags Tags
    Electrical
AI Thread Summary
The discussion focuses on solving a bridge circuit with initial resistances R1=100 ohms, R2=200 ohms, R3=250 ohms, and R4=300 ohms, using an input voltage of 3V. The user attempts to apply Ohm's Law to find the output voltage but struggles with the correct approach for a bridge circuit. A suggested method involves calculating the voltage at the positive and negative terminals using the equivalent resistances of the series and parallel configurations. The output voltage is calculated as -0.164V for the initial resistances and 0V when R1 is changed to 125 ohms, although there are noted discrepancies in the resistance values used. The discussion emphasizes the importance of correctly identifying resistances in bridge circuits for accurate voltage calculations.
ElBell
Messages
22
Reaction score
0

Homework Statement



A bridge initially has resistances equal to R1=100ohms, R2= 200ohms, R3= 250ohms, R4= 300ohms. Determine output voltage at this condition for an input voltage of 3V. What is the bridge output if R1 changes to 125ohms?

Homework Equations



Havent been given any. I am assuming something to do with Ohms Law?


The Attempt at a Solution



I used Ohms Law. But I don't know if I am on the right track.

I= E/ R
I= 3/ 850 = 0.00353 amps.

Now I don't know what to do. Or if I was even supposed to use this Law.

Any help would be much appreciated :) Thanks alot.
 
Physics news on Phys.org
I'm actually just learning about them myself so I could be wrong but I may be able to help. Firstly the equivalent resistance of parallel resistors isn't just the sum of resistances so that doesn't work because in a bridge you usually have two banks of resistors that are in series connected in parallel which is in turn connected to some sort of measuring device (galvanometer) at a point in between them.

So across that measuring device, you will have a positive and negative terminal and you want the potential difference between them

So, voltage across top of the circuit (current flows in direction of positive charge) = V = 3v

So the voltage in the (+) terminal is = V x (R2/ R(eq) of R1 and R2 in serial)
voltage in the (-) terminal is = V x (R4 / R(eq) of R3 and R4), just find the difference between them and I think that should be it.
 
Thanks for your help!

What does everything think of what I have done here?

Eo= Ei(R1/R1+R2) – (R3/R3+R4)
Eo= 3V (100/100+150) - )200/250+300)
= -.164V
Let us change R1 to 125 ohms:

Eo= Ei(R1/R1+R2) – (R3/R3+R4)
Eo= 3V (125/125+150) - )200/250+300)
= 0V
 
The method looks OK except you seem to be using the wrong values for some of the components.
R1=100ohms, R2= 200ohms, R3= 250ohms, R4= 300ohms in the first post.

You are using 150 ohms for R2 and 200 ohms for R3.
 
Back
Top