How to calculate resistance in a combined circuit using V&I

Click For Summary
To calculate resistance in a combined circuit using voltage and current, the formula R=V/I is essential. The user attempted to find the total resistance by first calculating the resistance of R1 and R2 in series, resulting in 400Ω, and then considering R3 in parallel with that combination. However, confusion arose regarding the correct values and calculations, particularly with the current readings and their conversions. The total resistance was further explored using the equation 1/Rt=1/R1 + 1/R3, but the calculations led to discrepancies. Clarification on the circuit configuration and accurate current values is necessary for proper resistance calculations.
Daniel2244
Messages
125
Reaction score
5

Homework Statement


I am not sure how to calculate the resistance of the circuit and each resistor using voltage and current. I know how to work the resistance out in series and parallel but am 100% how to work it out in combined.

Homework Equations


R=V/I, 1/Rt=1/R1+1/R2

The Attempt at a Solution


upload_2018-3-5_21-13-30.png

A1=5MA, A3=2.5MA, A5=1.7, and voltage is 1V
So, would I do 1/0.0025=400Ω (not correct max R should be 300Ω)? Maybe I should have added another ammeter between R1 and R2 or after R2 on the same branch?. Now, because I have the resistance worked out for the resistors in series would I work out the resistance for R3? R3=1/0.0017=588.24 (also very wrong)

upload_2018-3-5_21-27-42.png

Finally, by adding R1 and R2 turning it into one resistor (400Ω) could I turn the circuit into a parallel circuit to work out total resistance? 1/Rt=1/400+1/588.24.24=4.1999864e-3 Rt=1/4.1999864e-3=238.1Ω.
 

Attachments

  • upload_2018-3-5_21-13-13.png
    upload_2018-3-5_21-13-13.png
    33.4 KB · Views: 592
  • upload_2018-3-5_21-13-30.png
    upload_2018-3-5_21-13-30.png
    1.9 KB · Views: 585
  • upload_2018-3-5_21-27-21.png
    upload_2018-3-5_21-27-21.png
    2.3 KB · Views: 569
  • upload_2018-3-5_21-27-42.png
    upload_2018-3-5_21-27-42.png
    2.3 KB · Views: 549
Physics news on Phys.org
I couldn't read the attachment 1. If the first drawing in your attempt to solve is correct, you have R1 in series with R2. What is the total resistance in that branch?

Note that R3 is in parallel with the R1 + R2.

What is the value of R3 compared to R1 + R2?

In your attempt, what does the quantity 1/0.0017 represent?
 
Daniel2244 said:

Homework Statement


I am not sure how to calculate the resistance of the circuit and each resistor using voltage and current. I know how to work the resistance out in series and parallel but am 100% how to work it out in combined
This is NOT a problem statement. You don't tell us what is given and what is asked of you.

Sorry, but your attachments are illegible.
 
magoo said:
I couldn't read the attachment 1. If the first drawing in your attempt to solve is correct, you have R1 in series with R2. What is the total resistance in that branch?
https://gyazo.com/234be2533d0fe8a92cf622435f61d413 - this is the first attachment.

[/QUOTE]Note that R3 is in parallel with the R1 + R2.[/QUOTE] Yes, that's why I worked out the total resistance for R1 + R2 because they were is series. Then I worked out the resistance of R3 using R=V/I, the using the equation 1/Rt=1/R1+1/R3 (bearing in mind R1 is this equation is R1 and R2 added together) I worked out the total reistance

[/QUOTE]What is the value of R3 compared to R1 + R2?[/QUOTE]
R3=588.24 Ω R1+R2=400Ω
[/QUOTE]In your attempt, what does the quantity 1/0.0017 represent?[/QUOTE]
Resistance of R3. I changed 1.7mA to 0.0017A
 
BvU said:
This is NOT a problem statement. You don't tell us what is given and what is asked of you.
The results I got from the experiment carried out: A1=5MA, A3=2.5MA, A5=1.7, and voltage is 1V
Using these results I have to calculate the resistance of the total resistance of the circuit at 1v using the current.

Sorry, but your attachments are illegible.
Attachment 1: https://gyazo.com/234be2533d0fe8a92cf622435f61d413
Attachment 2:https://gyazo.com/d191a48c47c6c0f87df0163f7b89ae64
Ignore the numbers next to the ammeters they're not relevant.
 
Thread 'Correct statement about size of wire to produce larger extension'
The answer is (B) but I don't really understand why. Based on formula of Young Modulus: $$x=\frac{FL}{AE}$$ The second wire made of the same material so it means they have same Young Modulus. Larger extension means larger value of ##x## so to get larger value of ##x## we can increase ##F## and ##L## and decrease ##A## I am not sure whether there is change in ##F## for first and second wire so I will just assume ##F## does not change. It leaves (B) and (C) as possible options so why is (C)...

Similar threads

  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 14 ·
Replies
14
Views
1K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 19 ·
Replies
19
Views
7K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 60 ·
3
Replies
60
Views
10K
  • · Replies 13 ·
Replies
13
Views
2K
Replies
5
Views
2K