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Help with a circuit and Ohm's law

  • Thread starter magnifik
  • Start date
  • #1
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help with a circuit and Ohm's law!!

Homework Statement


ei1qgl.jpg


A) What is voltage V at terminal A with respect to ground?

B) Imagine that a wire is connected between terminals A and B. What is the current flowing through the battery?

C) With the wire connected between terminals A and B, what is the current flowing through the 2 Ω resistor?

D) Imagine that, instead of a wire, a 6Ω resistor is connected between terminals A and B. What is the current flowing through the battery?

Homework Equations


V=IR


The Attempt at a Solution


For part A, I know that the ground is the symbol at the bottom, but I do not know how to calculate the voltage.
For part B, I thought the answer would be 5A because V=IR gives 10=2I so I is 5, but that is incorrect.
For part C, I applied the same reasoning in B and that was wrong again.
For part D, I got 10=6I, which would give 1.67 but that's wrong.

Can someone please help me understand the concepts? I think that would provide a good start. I thought I just had to apply Ohm's Law but is there something more I must do?? Thanks.
 

Answers and Replies

  • #2
1,330
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Hi magnifik

A) Do you know the potential at B? The potential across AB is the same at the potential across 2 Ω resistor

B) and C) When there is wire connecting A and B, the current won't pass 2 Ω resistor

D) You have to find the total resistance and find the total current
 
  • #3
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A) I'm not sure what you mean by "potential"
B) and C) Does that mean that it would just be equal to the current passing through the 3 Ohm resistor??
D) for total resistance, would this circuit be series-parallel? not sure how to find the total resistance.. voltage is still 10V?

thanks for the help. i'm still a little lost though.
 
  • #4
360
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A) still unsure
B) since you said it doesn't pass through the 2 Ohm resistor, there is still the current from the 3 Ohm resistor, which is equal to 3.33
C) the answer should be 0, right? since you said it won't pass through that resistor at all
D) i found total resistance to be 4.5 and solving for I in Ohm's Law, I got 2.22 but then I tried just finding the current from each resistor, added it up and got 10. I don't know if either one is right??

am i making progress??????
 
  • #5
1,330
48


Hi magnifik

A) Potential means voltage. Because B is grounded, the potential at B will be ...
B) and C) yes that's right. Do you know why?
D) I = 2.22 A is right. You can't find the total current by adding all the current passing through the resistors because the current passing through 3 Ω is 2.22 A, which is the same as total current. The total current passing through 2 Ω and 6 Ω will also be 2.22 A

Let's try another. Can you find the total current passing through the circuit if it only contains 3 Ω and 2 Ω in series?
 
  • #6
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A) 0 volts at B? not sure how to get A
B & C) i can't say i know why. :T
d) yaaaay!

thanks so much for all the help!!!!!!!!! (:
 
  • #7
1,330
48


Hi magnifik

A) Yes, potential at B = 0. Now find potential of AB, which is the same as potential across 2 Ω resistor. Then, potential of AB = potential of A - potential of B

B) and C) Because we consider wire has a very low resistance so the current passing through it will be very large. almost all of the current. In ideal case, we consider all current passes through it.
 
  • #8
360
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resolved
 

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