Short Circuit Current, EMF, Internal Resistance

In summary, the conversation discusses an experiment to find the internal resistance and EMF of a battery pack. The person is now trying to determine the short circuit current, but is having trouble finding information. They propose a method to calculate the short circuit current, but there are concerns about the safety and accuracy of this approach. It is also mentioned that the internal resistance of a battery may not be constant and the resistance of the ammeter must be considered.
  • #1
geoff.bray
1
0
Okay so I have conducted an experiment to find the internal resistance of a battery pack by gradient of a graph of voltage against current. All so far okay.

I went on to find the EMF also, again all so far okay.

Now I need the short circuit current, and I can't find any information anywhere unbelievably. I don't know if its known otherwise elsewhere.

But anyway, I thought it would simply be EMF/Internal Resistance.

The battery pack is in series with 4 batteries, it is not parallel.

Can anyone confirm/disprove this for me?
 
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  • #2
geoff.bray said:
Okay so I have conducted an experiment to find the internal resistance of a battery pack by gradient of a graph of voltage against current. All so far okay.

I went on to find the EMF also, again all so far okay.

Now I need the short circuit current, and I can't find any information anywhere unbelievably. I don't know if its known otherwise elsewhere.

But anyway, I thought it would simply be EMF/Internal Resistance.

The battery pack is in series with 4 batteries, it is not parallel.

Can anyone confirm/disprove this for me?

You need to be careful shorting batteries in the real world. What is the context of the question? Is this for a school lab? If so, have they assured you that it is safe to short the battery pack to measure the short circuit current?
 
  • #3
"Internal resistance" is a loose term to describe the way a battery (or any power source) functions. The assumption is made that it is the same for all currents - i.e. that the battery is 'ohmic'. If you plot the voltage drop over a range of practical currents then you do get a straight line, which justifies this to an extent. I wouldn't say that measuring short circuit current would necessarily reveal the same answer, particularly if the battery gets cooked in the process. (Also, the resistance of the Ammeter would be a factor if the battery happened to be a really beefy one.)
The proposed experiment is fine as a thought exercise but not the best way to find out a useful property of the battery. And you could always blow it up if you're unlucky.
 
  • #4
If yo connect the terminals of a battery (generator) together the ' short circuit ' current equals emf/total resistance .
If the only resistance in the circuit is the internal resistance then you are correct
 
  • #5
That assumes that the resistance is the same for all currents. It may well not be because batteries are not made of metals so they can't be relied upon to follow Ohm's law and may well not have a fixed value of resistance.
Also, your current meter has resistance that needs to be taken into account.
 

1. What is short circuit current?

Short circuit current is the maximum current that can flow through a circuit when there is no resistance present. It occurs when the positive and negative terminals of a power source are directly connected, causing a large amount of current to flow.

2. How is short circuit current calculated?

Short circuit current can be calculated by dividing the voltage of the power source by the total resistance in the circuit. This calculation is known as Ohm's law (I=V/R).

3. What is EMF?

EMF, or electromotive force, is the potential difference between two points in an electrical circuit. It is measured in volts and represents the amount of energy that a power source can provide to the circuit.

4. How does internal resistance affect a circuit?

Internal resistance is the resistance present within a power source. It can affect a circuit by decreasing the voltage and increasing the current, leading to a decrease in the overall power output of the circuit.

5. How is internal resistance measured?

Internal resistance can be measured by using a voltmeter and ammeter to measure the voltage and current of a circuit with and without a load. The difference between the two measurements can be used to calculate the internal resistance (r=ΔV/ΔI).

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