Grounded circuit, 2 batteries and 2 resistors

  • #1
86
6

Homework Statement


Picture a circuit grounded at the left lower corner. Then as you go up the left side of the circuit, you have a 9V battery. The top left corner is labeled a. Then on the top of the circuit, you have a 2 ohms resistor. Then on the right side of the circuit, you have a 6V battery. The right lower corner is labeled b. Then on the bottom side of the circuit you have a 1 ohm resistor.
What is the value of the potential at points a and b?

Homework Equations


Kirchhoff's loop law
I = Epsilon/R
Delta Vr = - I*R


The Attempt at a Solution



First Kirchhoff's loop law to find the current in the circuit. I assumed the clockwise current was the same in both resistors.

--> 9V - 2 I - 6V - 1 I = 0
3V = 3I --> I = 1A

I know the potential at point a is 9V. The potential at the lower left corner, where the circuit is grounded, is zero. As you go up the circuit, you have gained 9 V by "passing through" the 9V battery.

Then you pass through the top resistor.
The potential difference across that resistor is given by delta Vr = - I * R = -1A*2omhs =-2V. So by the time you reach the right top corner, you are at 9V-2V= 7V.

Then you pass through the 6V battery. You go from the positive terminal to the negative terminal, so you lose 6V. Hence, at point b you are 7V-6V= 1V.

Is my reasoning any good?
 

Answers and Replies

  • #2
cnh1995
Homework Helper
Gold Member
3,444
1,144
Then as you go up the left side of the circuit, you have a 9V battery. The top left corner is labeled a. Then on the top of the circuit, you have a 2 ohms resistor. Then on the right side of the circuit, you have a 6V battery. The right lower corner is labeled b. Then on the bottom side of the circuit you have a 1 ohm resistor.
What is the value of the potential at points a and b?
What about polaritiy of the batteries? A diagram would be helpful.
 
  • #3
86
6
tmp_5375-20160331_170516-639066610.jpg
 
  • #6
CWatters
Science Advisor
Homework Helper
Gold Member
10,535
2,302
You can also get to b by going "up" through the 1 Ohm....

0 + (1*1) = 1V
 
  • #7
86
6
You can also get to b by going "up" through the 1 Ohm....

0 + (1*1) = 1V

True that.
 

Related Threads on Grounded circuit, 2 batteries and 2 resistors

Replies
6
Views
14K
Replies
7
Views
14K
  • Last Post
Replies
2
Views
2K
Replies
20
Views
4K
  • Last Post
Replies
4
Views
559
Replies
15
Views
883
Replies
3
Views
436
Replies
11
Views
5K
Replies
12
Views
4K
Replies
7
Views
8K
Top