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Found in: Page 772

### College Physics (Urone)

Book edition 1st Edition
Author(s) Paul Peter Urone
Pages 1272 pages
ISBN 9781938168000

# Given a battery, an assortment of resistors, and a variety of voltage and current measuring devices, describe how you would determine the internal resistance of the battery.

Internal resistance is ${\mathrm{R}}_{\mathrm{int}}={\mathrm{R}}_{\mathrm{tot}}-{\mathrm{R}}_{\mathrm{ext}.}$

See the step by step solution

## Step 1: Definition of internal resistance

Internal resistance is referred to as the opposed flow of current by the cells itself resulting in the generation of heat.

## Step 2:Calculating internal resistance

To determine the internal resistance of the battery, we need to have some information. The first would be raw voltage(${\mathrm{U}}_{\mathrm{raw}}$ ) with no current flowing through. Next, we need to attach to the circuit, between the poles, a resistor with known resistance ${\mathrm{R}}_{\mathrm{ext}}$ . Then we can calculate the expected current, which would happen if the source was perfect, with no internal resistance. After that, we can measure real current, ${\mathrm{I}}_{\mathrm{real}}$ , and calculate total resistance as:

${\mathrm{R}}_{\mathrm{tot}}=\frac{{\mathrm{U}}_{\mathrm{raw}}}{{\mathrm{I}}_{\mathrm{real}}}$

Finally, internal resistance is calculated as:

${\mathrm{R}}_{\mathrm{int}}={\mathrm{R}}_{\mathrm{tot}}-{\mathrm{R}}_{\mathrm{ext}}$