DC Motors – MME 3374A – Study Guide, Lecture Notes, and Exam Preparation
Material
What happens when a wire is moved through the airgap right at a velocity, v? - ANS ✔✔an
electromotive force will be induced in the wire
Force Generation - What happens if we subject the previous example to an electric current? -
ANS ✔✔a force will be acting upon the wire due to the interaction of the magnetic fields of the
wire and the magnetic fields within the air gap
How are velocity and induced emf related? - ANS ✔✔the faster the velocity of the wire, the
greater the induced emf (makes up the speed equation)
What happens to the voltage in the speed equation? - ANS ✔✔the voltage varies sinusoidally as
the loop turns in the magnetic field
What happens when current is applied to the loop in slide 19 from a battery? - ANS ✔✔-A
current will flow through the loop
-A force will be exerted on the wire loop causing it to accelerate to a speed ω
-As the wire loop turns in the magnetic field, a voltage will be induced in itproportional to the
velocity of rotation
What happens in this position (90 deg Mechanical from the horizontal) ? (from slide 20) - ANS
✔✔-The force exerted on the wire will reverse due to the direction of the current in the wire
relative to the magnetic field
-The wire loop will oscillate about the this position and eventually come to a stop
-A device must be used to reverse the direction on the current in the wire in order to maintain
torque in the same direction
What is a commutator? - ANS ✔✔a device that reverses the direction of the current so that a
constant, non-reversing torque is produced
Material
What happens when a wire is moved through the airgap right at a velocity, v? - ANS ✔✔an
electromotive force will be induced in the wire
Force Generation - What happens if we subject the previous example to an electric current? -
ANS ✔✔a force will be acting upon the wire due to the interaction of the magnetic fields of the
wire and the magnetic fields within the air gap
How are velocity and induced emf related? - ANS ✔✔the faster the velocity of the wire, the
greater the induced emf (makes up the speed equation)
What happens to the voltage in the speed equation? - ANS ✔✔the voltage varies sinusoidally as
the loop turns in the magnetic field
What happens when current is applied to the loop in slide 19 from a battery? - ANS ✔✔-A
current will flow through the loop
-A force will be exerted on the wire loop causing it to accelerate to a speed ω
-As the wire loop turns in the magnetic field, a voltage will be induced in itproportional to the
velocity of rotation
What happens in this position (90 deg Mechanical from the horizontal) ? (from slide 20) - ANS
✔✔-The force exerted on the wire will reverse due to the direction of the current in the wire
relative to the magnetic field
-The wire loop will oscillate about the this position and eventually come to a stop
-A device must be used to reverse the direction on the current in the wire in order to maintain
torque in the same direction
What is a commutator? - ANS ✔✔a device that reverses the direction of the current so that a
constant, non-reversing torque is produced
