Three resistor problems: Wheatstone bridge and series/parallel circuits

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mstehman88
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NEED HELP ASAP! Wheatstone bridge and DC series/parallel ! Please look!

I have three problems I need help solving.


Problem #1:
Fine the value R1 in the figure if R2 = 30ohm, I = 0.5A and V = 10V


My try was:

Rp = R1 + R2 , 20 = R1 + 30 , R1 = -10?

** please look for attached diagram problem 1

------------

Problem # 2

You have a balanced wheatstone bridge at L2= 45cm, mark ( where L2 + L3 = 100cm ) and R1 = 100ohm, what is the unkown resistance Rx?

** please look at attached diagram for problem 2

Problem #3.

Calculate the current of A in the figure if R1 = 250ohms, R2 = 400ohms, R3 = 200ohms and R4 = 200ohms

** please look at problem 3 for the diagram attached.

I had I = V/R with 45V/450 Ohm which gave me 0.1 A I combined the resistors to 400, 400, 250 on the diagram.
 
Attachments
  • Hand-marked circuit schematic with two branches in parallel between a battery labeled +V- and 10V: R2 in the upper branch with current I2 arrowed, and R1 in the lower branch with current I1 arrowed; total current labeled I = 0.5A.
    problem1.jpg
    23.4 KB · Views: 478
  • Handwritten Wheatstone bridge circuit with resistors Rx, R1, L2 and L3 on a slide-wire, a galvanometer G in the centre, and a battery at the bottom. Beside it is the problem text: balanced at L2 = 45 cm, L2 + L3 = 100 cm, R1 = 100 ohms, find Rx.
    problem2.jpg
    19.9 KB · Views: 497
  • Handwritten-annotated circuit schematic: a 45V battery in series with R1 feeding a parallel network of R2 and a branch with R3 and R4 in series, with an ammeter A in the bottom wire. Labels R3 200 and R4 200 written by hand; R1 250 ohm, R2 400 ohm printed.
    problem3a.jpg
    24.3 KB · Views: 488

Discussion



For problem #1, the total resistance is 20 ohm (10v/.5A). However, the formula for resistors in parallel is not what you're using. Parallel resistance is computed using 1/R(total) = 1/R(1) + 1/R(2) + ... You have R(total) and R(2) so the resistance for R(1) should be easy to solve.

For problem #2, I'm not sure what to make of that problem.

Problem #3 does have a current of .1A
 


Are u sure regarding problem 2's diagram?
THERE'S NO L1,L2.
 


Seems like problem 4 about the Wheatstone bridge is referencing some other problem that is on the paper. It says "you have balance THE Wheatstone bridge", usually it would be written as "you have balanced A Wheatstone bridge".
 


The problem numbers on the paper don't match what I've posted here. But that's all that was given :( I have no idea