The following relation can be used to calculate the resistance as the net voltage in the form of the difference between the source voltage and the back voltage.

$\overline{){\mathbf{i}}{\mathbf{=}}\frac{{\mathbf{V}}_{\mathbf{s}}\mathbf{-}{\mathbf{V}}_{\mathbf{b}}}{\mathbf{R}}}$, where V_{s} is the source voltage, V_{b} is the back voltage, i is current, and R is the armature resistance.

R = (V_{s} - V_{b})/i = (6.00 - 4.50)/3.00 = 0.5Ω

The motor in a toy car operates on 6.00 V, developing a 4.50 V back emf at normal speed. If it draws 3.00 A at normal speed, what current does it draw when starting?

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Resistors and Ohm's Law concept. You can view video lessons to learn Resistors and Ohm's Law. Or if you need more Resistors and Ohm's Law practice, you can also practice Resistors and Ohm's Law practice problems.