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DC Motors

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DC Motors

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    1. Lab 7 P. 1 Autumn Quarter DC Motors Lab 7

    2. Lab 7 P. 2 Autumn Quarter Magnetism Instructor: With magnetic fields, opposite poles attract and like poles repel.Instructor: With magnetic fields, opposite poles attract and like poles repel.

    3. Lab 7 P. 3 Autumn Quarter Magnetic Fields Instructor: A magnetic field can be drawn so that the field lines emanate from the North pole and go toward the South pole of the magnet. The field is stronger where the field lines are more dense, so the field is stronger at the poles and weaker farther away from the poles.Instructor: A magnetic field can be drawn so that the field lines emanate from the North pole and go toward the South pole of the magnet. The field is stronger where the field lines are more dense, so the field is stronger at the poles and weaker farther away from the poles.

    4. Lab 7 P. 4 Autumn Quarter Electric Currents > Magnetism! Instructor: Current running through a wire creates a magnetic field. This version of the “right hand rule” shows the thumb running in the direction of the current, and the magnetic field curves around the wire in the direction that the fingers curl.Instructor: Current running through a wire creates a magnetic field. This version of the “right hand rule” shows the thumb running in the direction of the current, and the magnetic field curves around the wire in the direction that the fingers curl.

    5. Lab 7 P. 5 Autumn Quarter Right Hand Rule Instructor: In the case of a circular loop of current, the thumb goes in the direction of the current loop, and the fingers curl inward in the direction of the magnetic field. Instructor: In the case of a circular loop of current, the thumb goes in the direction of the current loop, and the fingers curl inward in the direction of the magnetic field.

    6. Lab 7 P. 6 Autumn Quarter Electromagnetism Instructor: The same current loop as before, with the magnetic field shown. The looping current creates a magnetic field that is much stronger through the center of the loop than outside the loop. The field in the middle of the loop also approximates a straight line. The current loop acts as an electromagnet. When the current through the loop stops, the magnetic field disappears.Instructor:

    7. Lab 7 P. 7 Autumn Quarter Electromagnet Instructor: If the many current loops are put together in a coil, the magnetic field strength increases, creating an even more powerful current-controlled magnetic field.Instructor: If the many current loops are put together in a coil, the magnetic field strength increases, creating an even more powerful current-controlled magnetic field.

    8. Lab 7 P. 8 Autumn Quarter Force in a Conductor Instructor: As seen previously with the bar magnets, magnetic fields that come near each other create a force. In the example shown, the current is flowing through a wire that passes through a horseshoe magnet. The magnetic field from the horseshoe magnet interacts with the wire current, causing a downward force on the wire. Note: Another right-hand rule can be used to remember the direction of the interacting forces. The index finger points in the same direction of the current flow, the middle finger is perpendicular to the index finger and points in the direction of the magnetic field, and the thumb (pointing perpendicular to both the index and middle fingers) points in the direction of the resulting force.Instructor: As seen previously with the bar magnets, magnetic fields that come near each other create a force. In the example shown, the current is flowing through a wire that passes through a horseshoe magnet. The magnetic field from the horseshoe magnet interacts with the wire current, causing a downward force on the wire. Note: Another right-hand rule can be used to remember the direction of the interacting forces. The index finger points in the same direction of the current flow, the middle finger is perpendicular to the index finger and points in the direction of the magnetic field, and the thumb (pointing perpendicular to both the index and middle fingers) points in the direction of the resulting force.

    9. Lab 7 P. 9 Autumn Quarter Force in a Conductor Instructor: When only the current flow is reversed (by reversing the polarity of the battery, in this example), the force reverses direction and now goes up.Instructor: When only the current flow is reversed (by reversing the polarity of the battery, in this example), the force reverses direction and now goes up.

    10. Lab 7 P. 10 Autumn Quarter Diagram of a Simple DC Motor Instructor: The DC motor utilizes this concept by changing the direction of the current flowing through the brushes into the coiled wire in the armature. A permanent magnet creates a constant magnetic field, and when current runs through the coils, a force is created that turns the armature. When the armature has turned far enough, the brushes are now in contact with the opposite ends of the coiled wire, effectively reversing the polarity of the voltage across the coil and reversing the current flow, which create a force that spins the armature further in the same direction. This process repeats as long as voltage is supplied to the motor, creating the motor rotational force.Instructor: The DC motor utilizes this concept by changing the direction of the current flowing through the brushes into the coiled wire in the armature. A permanent magnet creates a constant magnetic field, and when current runs through the coils, a force is created that turns the armature. When the armature has turned far enough, the brushes are now in contact with the opposite ends of the coiled wire, effectively reversing the polarity of the voltage across the coil and reversing the current flow, which create a force that spins the armature further in the same direction. This process repeats as long as voltage is supplied to the motor, creating the motor rotational force.

    11. Lab 7 P. 11 Autumn Quarter Commutator Instructor: The brushes come into contact with the commutator, which connects to the lead wires of the armature coil. The commutator spins with the rest of the armature and the sides of the commutator change which brush they touch with every half-revolution. This reverses the current flow.Instructor: The brushes come into contact with the commutator, which connects to the lead wires of the armature coil. The commutator spins with the rest of the armature and the sides of the commutator change which brush they touch with every half-revolution. This reverses the current flow.

    12. Lab 7 P. 12 Autumn Quarter

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