Journal #15 2/22/12. Use what you learned in yesterday’s lab to predict which picture shows magnetized atoms and which shows non-magnetized atoms. Electromagnetism. Ch. 24-25 Quiz – Formulas and Vocabulary – Wednesday, 2/29 Test – Ch. 24-25 – Friday, March 2. Magnets.
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Quiz – Formulas and Vocabulary – Wednesday, 2/29
Test – Ch. 24-25 – Friday, March 2
computer hard drives, and
high speed trains.
When DC electricity is passed through a wire, a magnetic field rotates around the wire in a specific direction.
“RightHandRule”-If you take your right hand and wrap it around the wire, with your thumb pointing in the direction of the electrical current (positive to negative), then your fingers are pointing in the direction of the magnetic field around the wire.
Current to the right
Magnetic field towards you above the wire and away from you below the wire
Current out of the page
Counterclockwise magnetic field
Current into the page
Clockwise magnetic field
Magnetic field towards you outside the loop and away from you inside the loop
The primary voltage (on the left) induces a magnetic field in the core, which creates the secondary voltage (on the right).
What makes transformers so useful is that if you change the number of turns from one side to the other, you change the voltage in the wire on the right!
Transformers can change a high voltage to a lower one, or a low voltage to a higher one.
The magnets must be arranged in the rotor in a specific pattern in order for the electromagnet to effectively “push and pull” it continuously
The commutator discs have different numbers of alternating clear/black edges
A photogate will be placed in this position so that it can measure the frequency of color changes. That information will be used to calculate the rotational speed of the disc/motor
4 D-cell batteries provide potential difference to the circuit containing the electromagnet
The electromagnet has a sensor on the end that detects dark or clear and reverses the current alternating it’s polarity
The rotor is freely spinning on ball bearings, but the commutator discs must be firmly attached with the washer so that they don’t shift