Science- Cells in Parallel?

Question

I have to write a lab about cells in parallel. I had to make an electric circuit with 1 bulb and 1 cell. Then I added another cell, and then another one.

The question is:

As more cells are added in parallel, what is the effect on:

-bulb brightness

-current

-voltage supply (across the cell)

-voltage drop (across the bulb)

The results obtained from doing this experiment were very unreliable because of the equipment. Please help!

Answer 1

With cells in parallel, the voltage remains the same (for identical cells), and the ability to supply more current increases with each cell added.

- bulb brightness will remain the same UNLESS it was starved for current with only one cell.  That is, if one cell cannot supply enough current, then 2 cells should be able to supply enough current for full brightness.

- current will remain the same because the load (bulb) is the same, and it will only draw as much current as it needs.  However, if the bulb was starved for current with only one cell, then it will get brigher with 2 cells, but probably not any brighter as you add more cells.

- both the voltage supply and the voltage drop across the bulb will remain the same as more cells are added in series.

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Answer 2

This lab shows where the ideal case and the real one diverge.

In an ideal case, as more cells are added in parallel, there is no effect on:

-bulb brightness

-current

-voltage supply (across the cell)

-voltage drop (across the bulb)

But in reality, every cell has some ESR (equivalent series resistance) in it.  Typically the ESR is on the order of a few ohms, and is modeled as such in real-life circuits.

Thus, as you add cells in parallel with your bulb, you actually may see a difference in any of the above quantities, exclusively due to ESR.  It will be especially pronounced if the bulb draws a significant load on your cells.