Explain the principle of magnetism upon which electric motors operate
What will be an ideal response?
A strong magnet is made by wrapping many coils of insulated wire around an iron core and passing
electrical current through the wire. When the current stops flowing, the magnetic field ceases to exist.
If the wires are switched to opposite battery terminals, the poles of the magnet will reverse but the
magnetic field will remain. This unit is called an electromagnet. Bending the electromagnet into the
shape of a horseshoe and suspending a permanent magnet on a bearing between the poles will attract
each other causing the permanent magnet to make a half turn. A device called a commutator causes the
motor to run continuously in the same direction.
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The reinforced concrete in a slurry wall (deep wall foundation) can range in thickness from 18 inches to _____.
a. 5 feet b. 54 inches c. 4 feet d. 36 inches
What cable is preferred when wiring a security system?
A. Copper clad aluminum B. 18-22 AWG, twisted 2-wire, stranded C. Not smaller than 14 AWG copper D. Any CAT 5 cable
When xeriscaping, factors that should be considered include all of the following EXCEPT ____
a. restricted water availability b. use of low-moisture plants such as succulents c. narrow spacing between plants d. precision irrigation
The temperature of the air that surrounds an object on all sides is called ________ temperature.
Fill in the blank(s) with the appropriate word(s).