Resistors and Ohm's Law Video Lessons

Concept

Problem: 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?

FREE Expert Solution

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 Vs is the source voltage, Vb is the back voltage, i is current, and R is the armature resistance.

R = (Vs - Vb)/i = (6.00 - 4.50)/3.00 = 0.5Ω

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Problem Details

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?