Question

An electric motor rotates a wheel at a constant angular velocity 10rps while opposing torque is 10Nm. The power of that electric motor is:
A. 120W
B. 628W
C. 314W
D. 3.14W

Answer 1

An electric motor is a device which converts electrical energy into mechanical energy. The rectangular coil in it moves with angular velocity ω. The power generated by the electric motor depends on the product of torque and angular velocity.

Formula used:
Angular velocity, $\omega =rpm\times 2\pi$
Also power in rotation is given by:
$P=\tau \times \omega$
Where, τ= torque, ω=angular velocity.

Complete step-by-step answer:
An electric motor is an electrical machine which is used to convert electrical energy into mechanical energy. In an electric motor the current carrying conductor (form of wire) is placed perpendicular to the magnetic field and this experiences a force.
The current carrying conductor is placed at right angles to experience opposite directed forces.
The magnetic field is produced by electromagnets, interacts with the electrical energy and forms force which further create a torque. This torque causes the movement of an axle which rotates at the other end.
In the electric motor, there is a rectangular coil which is placed between the two shoe shaped magnets which produce magnetic fields. This magnetic field causes force which rotates the motor.
Now, it is given that angular velocity is 10rpm.
So, $\omega =10\times 2\pi$
Also power of the motor,
$\begin{aligned} & P=\tau \times \omega \\\ & \Rightarrow P=10\times 20\pi \\\ & \Rightarrow P=200\times 3.14 \\\ & \Rightarrow P=628W \\\ \end{aligned}$
Hence, Power of the electric motor comes out to be 628W.

So, the correct answer is “Option B”.

Note: An electric motor converts electrical energy into mechanical energy by gaining rotational motion. The angular velocity is given in rpm means rotational speed in revolutions per minute. It has a faster response rate and can drift large machines connected to it.