What is the current in a circuit with two cells?

In summary, the potential changes in a closed circuit can be either rises or drops, with sources typically responsible for rises and resistors for drops. The total amount of EMF that can drive current in a loop can be determined by summing up the EMFs in that loop, ignoring any resistances. In this particular circuit, the net EMF is zero, meaning the current will also be zero. The EMF, or Electromotive force, refers to the potential across the battery without any internal losses due to internal resistance.
  • #1
BMW
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0

Homework Statement


What is the current in this circuit:
http://img802.imageshack.us/img802/4646/8ekh.png

Homework Equations


All potential differences in a closed portion of a circuit must add to 0.
Terminal Voltage = EMF - I x internal resistance.

The Attempt at a Solution


I do not know how to do this, the answer says the current is 0A. I have no idea why.
 
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  • #2
You forgot the Relevant Equations portion of the template. What circuit laws have you learned about?
 
  • #3
gneill said:
You forgot the Relevant Equations portion of the template. What circuit laws have you learned about?

Sorry, I have added them in.
 
  • #4
Okay, so potential changes come in two flavors: Rises and drops. Typically sources are responsible for potential rises and resistors for potential drops.

If you "walk" around an isolated loop in a given direction and sum up just the changes in potential due to the sources you'll arrive at the total amount of EMF that can drive current in that loop. What do you find when you do this "walk" around your loop?
 
  • #5
gneill said:
Okay, so potential changes come in two flavors: Rises and drops. Typically sources are responsible for potential rises and resistors for potential drops.

If you "walk" around an isolated loop in a given direction and sum up just the changes in potential due to the sources you'll arrive at the total amount of EMF that can drive current in that loop. What do you find when you do this "walk" around your loop?

I'm getting confused with EMF, terminal voltage and internal resistance etc... isn't the 1.5V the EMF, which means that the actual potential rise (terminal voltage) will be less that 1.5V?

If I were to add up the EMFs, I would be assuming no current is flowing.
 
  • #6
BMW said:
I'm getting confused with EMF, terminal voltage and internal resistance etc... isn't the 1.5V the EMF, which means that the actual potential rise (terminal voltage) will be less that 1.5V?

The EMF, or "Electromotive force", refers to the potential across the thing inside the battery that produces the potential difference, and ignored any internal losses due to internal resistance. It's the potential that you would measure across the cell if you were to employ a perfect voltmeter that draws no current (so there would be no drop across any internal resistances).

In summing up the EMFs that are driving current in the circuit, ignore all resistances no matter where they are located and concentrate on the raw EMF values. You want to find out what the total EMF available to drive current is, not the effects of the current (not yet, anyways!).
 
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  • #7
gneill said:
The EMF, or "Electromotive force", refers to the potential across the thing inside the battery that produces the potential difference, and ignored any internal losses due to internal resistance. It's the potential that you would measure across the cell if you were to employ a perfect voltmeter that draws no current (so there would be no drop across any internal resistances).

In summing up the EMFs that are driving current in the circuit, ignore all resistances no matter where they are located and concentrate on the raw EMF values. You want to find out what the total EMF available to drive current is, not the effects of the current (not yet, anyways!).

Aha! So the net EMF is what creates a current in a closed circuit or part of a circuit? And the net EMF in this circuit is zero so the current will also be zero?

:D
 
  • #8
BMW said:
Aha! So the net EMF is what creates a current in a closed circuit or part of a circuit? And the net EMF in this circuit is zero so the current will also be zero?

:D

Exactly! :smile:
 
  • #9
gneill said:
Exactly! :smile:

Thank you for your time :biggrin:
 

1. What is a circuit with two cells?

A circuit with two cells is an electrical circuit that contains two sources of electrical energy, typically batteries, connected in series or parallel. This allows for a higher voltage or longer lasting power supply.

2. How does a circuit with two cells work?

In a series circuit with two cells, the positive terminal of one cell is connected to the negative terminal of the other cell, resulting in a cumulative voltage. In a parallel circuit, both cells are connected to the same components, providing a longer lasting power supply.

3. What are the advantages of using a circuit with two cells?

One advantage is that using two cells in series can provide a higher voltage, which may be necessary for certain devices. Additionally, using two cells in parallel can provide a longer lasting power supply for devices that require more energy.

4. What precautions should be taken when using a circuit with two cells?

It is important to make sure that the cells are connected with the correct polarity to avoid damaging the circuit or any connected devices. Additionally, care should be taken to not short-circuit the cells, as this can cause them to overheat and potentially explode.

5. How do you calculate the total voltage and current in a circuit with two cells?

In a series circuit, the total voltage is the sum of the individual cell voltages. In a parallel circuit, the total voltage remains the same as the individual cell voltage, but the total current is the sum of the individual cell currents. This can be calculated using Ohm's Law, which states that voltage is equal to current multiplied by resistance (V=IR).

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