Electric Motor Physics Example 1

Follow the full solution, then compare it with the other examples linked below.

Example 1

easy
A DC motor draws 4 A4 \text{ A} from a 12 V12 \text{ V} supply. If the motor is 80%80\% efficient, what is its useful mechanical power output?

Solution

  1. 1
    Electrical power input: Pin=VI=12×4=48 WP_{\text{in}} = VI = 12 \times 4 = 48 \text{ W}.
  2. 2
    Useful mechanical power: Pout=η×Pin=0.80×48=38.4 WP_{\text{out}} = \eta \times P_{\text{in}} = 0.80 \times 48 = 38.4 \text{ W}.
  3. 3
    The remaining 9.6 W9.6 \text{ W} is lost as heat in the coils and friction.

Answer

Pout=38.4 WP_{\text{out}} = 38.4 \text{ W}
An electric motor converts electrical energy to mechanical energy. The efficiency tells us what fraction of the input power becomes useful work; the rest is wasted as heat and friction.

About Electric Motor

A device that converts electrical energy into mechanical energy (rotational motion) by exploiting the force exerted on a current-carrying conductor placed in a magnetic field.

Learn more about Electric Motor →

More Electric Motor Examples

Example 2 medium

A motor coil has [formula] turns, area [formula], carries [formula], and is in a [formula] field. Wh

Example 3 medium

An electric drill motor operates at [formula] and draws [formula]. It produces a torque of [formula]

Example 4 hard

A DC motor has a back-EMF of [formula] when running at full speed. The supply voltage is [formula] a

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