Question

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.

Short answer

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

Step-by-step solution

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:

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