Lesson 4: Electric Motors

Question 1

What is the basis of an electric motor?

Answer 1

• A coil of wire, carring a current in a magnetic field will tend to rotate. This is the basis of an electric motor.

Question 2

In the coil, how is the current and forces on both sides of the loop different (when the coil is placed in a magnetic field?)

Answer 2

• The current is flowing in OPPOSITE directions on each side of the loop.
• The wire will experience forces that act in opposite directions on either side of the coil (one will act upwards/ one will act downwards.)

Question 3

Because the wire will experience an upwards force and a downwards force at the same time (when in a magnetic field) what will happen to the wire?
What is the eventual issue?

Wink wink…. think rotations!!

Answer 3

• The wire will rotate.
• Once the loop is at 90 degrees (a half- loop has occurred, the wire will stop rotating.)

Question 4

How can we solve the problem of the wire (in the magnetic field) stopping rotating after a half loop/ once it has reached 90 degrees? What DEVICE do we use to do this?

Answer 4

• Switch the direction of the current when the loop passes 90 degrees.
• Do this using: split- ring commutator.
• The forces experienced by the wire will be in the same positions as they were intially.
• So, split ring commutator allows the motor to keep spinning in the same direction/ ensures the current in left and right hand side of coil is always going in same direction.

Question 5

Why does the wire stop moving when it is at 90 degrees?

Answer 5

• The curent on left/ right - hand side of coil switches direction.
• So, the force on the left and right- hand side of the coil would’ve switched: pushing the wire back to its original position.