Calculating Internal Resistance of a Voltage Source from Terminal Voltage Drop

In summary, the question is asking for the internal resistance of a voltage source when its terminal voltage decreases by 2 V and the current supplied increases by 5 A. The formula used is E = V - Ir and the given values are plugged in to solve for r, which is equal to -0.4 ohms. However, this answer is incorrect as there are too many unknowns since the value of Rload is not given. Additionally, the emf of the voltage source cannot be found with the given information.
  • #1
nautica
Okay here is the question:

a) what is the internal resistance of a voltage source if its terminal voltage drops by 2 V when the current supplied increases by 5 A.

b) Can the emf of the voltage source be found with the information supplied?

I know that E = V - Ir, and I am pretty sure that a simple algebraic equation can be put together. So what formulat am I missing??

Thanks
Nautica
 
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  • #2
You know that E = V - Ir so ΔE= ΔV- ΔI r. You are told that ΔE= 2volts when &Dekta;I= -5 amps. Of course, ΔV= 0 since the voltage source is fixed.
Thatis: 2= -5r. Can you solve for r now? :smile:.

The answer to b is NO. In effect V is the "constant of integration" when you "integrate" dE= -rdI. There is no way to find that from the information given.
 
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  • #3
I am in College Physics, we can not use calculus for an answer. So is there a reason algebraically.

thanks
nautica
 
  • #4
If u know the potential diff b/w two terminals, then u can find the emf.

With this information u cannot find
 
  • #5
So ther is no way to find emf without Potential difference?

thanks
nautica
 
  • #6
Okay For a) here is what I got

V=E-Ir

or dV=dE - dIr

2V = -5r

so r = -.4Ohms

BUT, my instructor said this was wrong b/c there I did not no the Rload and there are too many unknowns for this to be solved.

I can see how part B could not be solved but this looked so simple for part a)

He said this was the other equation I should have considered, but I do not see why it was needed.

I = E / (Rload + r)

Thanks
nautica
 

1. What is EMF?

EMF stands for electromotive force, which is the energy that drives an electric current. It is measured in volts.

2. What is terminal voltage?

Terminal voltage is the voltage that is present at the terminals of a battery or other power source. It is the actual voltage that is available to power a circuit.

3. How is EMF different from terminal voltage?

EMF is the potential difference created by a power source, while terminal voltage is the actual voltage that is available to power a circuit. Terminal voltage is always lower than EMF due to internal resistance in the power source.

4. What factors affect EMF and terminal voltage?

The strength of the magnetic field, the number of turns in the coil, and the speed of the motion of the coil are all factors that can affect EMF. Terminal voltage can be affected by the resistance of the circuit and the internal resistance of the power source.

5. How can EMF and terminal voltage be measured?

EMF can be measured using a voltmeter and a circuit containing a power source and a resistor. Terminal voltage can also be measured using a voltmeter, but it must be connected in parallel to the circuit to get an accurate reading.

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