Explaining Why Dry Cell Battery Resistance Increases & Power Pack Resistance

In summary, the internal resistance of a battery increases as the battery is used. This is due to the acid getting weaker and there being less ions to carry the charge. Additionally, the increased temperature of the wire causes the resistance to increase.
  • #1
Canuck156
32
0
Hi,

I just need a proper explanation as to why the internal resistance of a dry cell battery increases as the battery is used?

Also, what would cause the internal resistance, if there is any, in a power pack? (A power pack is a device that allows electricity from a powerpoint to be lowered to 2-12 Volts, suitable for experimental purposes.)

Thanks in advance for any help.

Canuck156
 
Last edited:
Physics news on Phys.org
  • #2
Canuck156,
1) I guess the reason is the acid inside getting weaker as it dissolves the electrodes.
2) Due to hysteresis, you lose some energy in the transformer's core, producing heat, which probably is the cause of output resistance.
 
  • #3
When a battery is part of a flowing circuit, it too must be part of the conducting loop. The electric flow in the battery is due to the flow of ions through a solution (in a wet cell). As the electrolytic solution (the acid or alkaline) is "used up" in the chemical reaction, there are fewer and fewer ions to carry the charge, therefore it's harder for the battery's own emf to push charges through itself. Hence: larger internal resistance.

Side note: if you are ever given the choice of having a "fully charged" car battery, or a "dead" car battery dumped on you, choose the latter.

Second question: A little nifty phenomenon called "self-induction" introduces "impedence" which has the same effect as "resistance" and is also measured in ohms. On top of that, all wires have resistance, and a transformer will have a lot of wire inside it. wound around and around. Also, as the current in a wire increases, the temperature of the wire increases (check your toaster for validity). As the temperature of a wire increases, the resistance of that wire increases. So the internal resistance of a transformer will also increase as the current through it increases.
 
  • #4
Thanks for the help, I now understand the second question that I posted. However, is the explanation regarding the acid still relevant for a 'dry cell' battery? (As specified in the original post) ?
 
  • #5
The typical dry cell uses the chemical reaction between zinc and manganese dioxide. I don't remember the specifics, but the reaction itself is not so straightforward, so a chemistry type person would give you a better answer if you need detail

As the zinc is turned into zinc oxide, it stops being a metal (now it's a compound) and thus is not a good conductor anymore. The layer of zinc oxide gets thicker and thicker and so there is more and more non-conductive stuff for the electrons to flow through.
 
  • #6
Thankyou, that has now answered both of my original question.

Thanks for the help!
 

1. What is a dry cell battery and how does it work?

A dry cell battery is a type of electrochemical cell that converts chemical energy into electrical energy. It consists of a positive electrode (cathode), a negative electrode (anode), and an electrolyte solution. When the battery is connected to a circuit, a chemical reaction occurs between the electrodes and the electrolyte, producing a flow of electrons and generating electrical energy.

2. Why does the resistance of a dry cell battery increase over time?

The resistance of a dry cell battery increases over time due to a process known as passivation. This is when a layer of insulating material, such as zinc oxide, forms on the surface of the electrodes, hindering the flow of electrons and increasing the resistance of the battery. This can also be caused by the depletion of the battery's chemicals and the buildup of impurities in the electrolyte solution.

3. How does the resistance of a power pack affect the performance of a dry cell battery?

The resistance of a power pack can greatly affect the performance of a dry cell battery. If the power pack has a high resistance, it will limit the flow of current from the battery, reducing the amount of power that can be delivered to the circuit. This can result in a shorter battery life and a decrease in the overall performance of the battery.

4. What factors can contribute to an increase in the resistance of a power pack?

There are several factors that can contribute to an increase in the resistance of a power pack, including the quality and age of the components, the design of the power pack, and the temperature at which it is operated. The type of material used for the conductors and the connections between components can also play a role in the overall resistance of the power pack.

5. How can the resistance of a dry cell battery and power pack be reduced?

The resistance of a dry cell battery and power pack can be reduced by ensuring that all connections are clean and free of corrosion, using high-quality components, and keeping the battery and power pack at a suitable operating temperature. Additionally, regularly replacing old or depleted batteries and power packs can help maintain lower resistance levels and improve overall performance.

Similar threads

  • Introductory Physics Homework Help
Replies
7
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
959
  • Introductory Physics Homework Help
Replies
14
Views
2K
  • Introductory Physics Homework Help
Replies
3
Views
2K
  • Electrical Engineering
Replies
14
Views
963
  • DIY Projects
Replies
3
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
2K
Replies
7
Views
907
  • Introductory Physics Homework Help
Replies
32
Views
7K
Replies
4
Views
2K
Back
Top