Slide 2:
Electricity & Magnetism (Simple DC Electric Motor)
Slide 3:
Electricity & Magnetism (Simple DC Electric Motor)
What are the components? 9V battery battery snap with leads magnet insulated wire wood base conductive stand
Slide 4:
Electricity & Magnetism (Simple DC Electric Motor)
How does it work? Motors covert electrical energy (from a battery or voltage source) into mechanical energy (used to cause rotation).
The principle of any electric motor is based on simple electromagnetism. When a current flow through a conductor, it generates a magnetic field; when this is place in a region of space that has a external magnetic field, the wire experiences a force.
The size of the force, which determines how fast the motor spins, depends on:
the amount of current in the wire
the length of the wire
the strength of the magnetic field Force = (current) x (wire length) x (magnetic field)
Slide 5:
Electricity & Magnetism (Simple DC Electric Motor)
How does it work? The direction of the force, which determines which direction the motor spins, depends on:
the direction of the current in the wire
the direction of the magnetic field
The Right Hand Rule is use to determine the direction of the force when the direction of the current and the direction of the magnetic field are know. Note that the force acting on the conductor is strongest when the direction of the current is perpendicular to the direction of the external magnetic field. There will be not force acting on the conductor when the direction of the current is parallel to the direction of the external magnetic field.
Slide 6:
Electricity & Magnetism (Simple DC Electric Motor)
How does it work? magnet non-stripped section of a conductor stripped section of a wire magnetic fields from magnet direction of current Top of Loop
Thumb: direction of current = left
Fingers: direction of magnetic field = up
Palm: direction of force = into plane of paper Bottom of Loop
Thumb: direction of current = right
Fingers: direction of magnetic field = up
Palm: direction of force = out of plane of paper Since the top of each loop experiences a force directed into the plane of the paper and the bottom of each loop experiences a force directed out of the plane of the paper, the rotor experiences a “torque”or tendency to rotate and begins to turn.
Slide 7:
Electricity & Magnetism (Simple DC Electric Motor)
Why the need for half insulated conductor? Consider the rotor after the loop has completed a half of a turn. The bottom section (carrying rightward current) quickly becomes the top section (carrying leftward current). The current that use to direct the force out of the plane of the paper is all of a sudden directed into the plane of the paper.
Likewise, the top section (carrying leftward current) quickly become the bottom section (carrying rightward current). The current that use to direct the force into the plane of the paper is all of a sudden directed out of the plane of the paper.
When this happen and left on its own, the rotor would never make a single complete rotation. The rotor would oscillate back and forth, first turning 180O one way, then 180O the other way, and so on, never completing more than half of a turn.
A simple technique would be momentarily turns off the flow of current to eliminate this problem and thus allowing the rotor to turn continuously.
Slide 8:
Electricity & Magnetism (Simple DC Electric Motor)
Why the need for half insulated conductor? For this experiment, we only stripped the top half of the insulated wire.
The current is complete when the stripped section comes into contact with the conductor stands, the rotor experiences a torque in the direction determined by the Right Hand Rule.
The rotor completes 180O turn and the circuit is broken as the non-stripped section of the wire comes into contact with the conductor stands. No current flows, therefore no opposing forces are experienced and the rotor does not get push into a cycle of alternating half turns.
Instead, the inertial force from the initial half turn carries the rotor the rest of the way around until it had completed a single turn. At this point, the stripped section of the wire again comes into contact with the conductor stands, completing the circuit and begins another cycle. Hence, the rotor spins continuously. Thank You