# Is it really ok to assume that internal resistance of a cell is 0?

• leojun
In summary, the presence of internal resistance in a cell can introduce errors in a circuit's output, and whether or not this is acceptable depends on the size of the resulting error, the accuracy required for the application, and the size of other errors. The internal resistance can also vary, affecting the voltage delivered by the cell.
leojun
is it really ok to assume that internal resistance of a cell is absent in a circuit
?

It depends on the application. Assuming that the internal resistance is 0 will introduce some error in your circuit's output. Whether or not that is OK depends on the size of the resulting error, the size of other errors, and the required accuracy for the application.

leojun
leojun said:
is it really ok to assume that internal resistance of a cell is absent in a circuit

Sometimes, not always.

Consider a small 9V battery like this http://www.westwealdfalconry.co.uk/_productimages/Duracell.jpg If that battery is powering just a small resistor & LED then the current draw will be low (perhaps 10mA). There won't be much voltage drop due to the internal resistance of the cell so the battery voltage will be close to 9V.

On the other hand if you tried to use the same battery to power a 50W light bulb the current required would be large (50/9 = 5.6A). The voltage drop due to the internal resistance would be very large. So large that the voltage wouldn't actually be anywhere near 9V (edit: You would have to factor in the internal resistance to calculate the actual current because 50/9 would no longer be accurate enough).

The internal resistance of a battery can also change so that when new (fully charged) it may deliver 9V on load, but then as the battery discharges the resistance increases so that when nearly flat it only produces 9V off load. As soon as you connect the load the voltage falls.

leojun

## 1. Can internal resistance of a cell ever be truly 0?

No, it is physically impossible for the internal resistance of a cell to be exactly 0. All materials have some degree of resistance, including the electrolyte materials used in batteries.

## 2. What factors affect the internal resistance of a cell?

The internal resistance of a cell can be affected by various factors such as the type of materials used in the electrodes and electrolyte, the temperature, and the age and condition of the cell.

## 3. Why is it commonly assumed that internal resistance of a cell is 0?

In many cases, the internal resistance of a cell is small enough to be negligible in calculations and experiments. This approximation simplifies the analysis and allows for easier understanding of the behavior of the cell.

## 4. How do we measure the internal resistance of a cell?

The internal resistance of a cell can be measured by using a multimeter to measure the voltage drop across a known resistor connected in series with the cell. The internal resistance can then be calculated using Ohm's Law.

## 5. Does the internal resistance of a cell affect its performance?

Yes, the internal resistance of a cell can affect its performance by causing a voltage drop and reducing the amount of usable energy that can be extracted from the cell. It can also affect the cell's ability to provide a consistent output of power.

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