Basic Electromagnetism and Electromagnetic Induction
When lightning strikes, nearby magnetic compass needles may be seen to jerk in response to the electrical discharge. No compass needle deflection results during the accumulation of electrostatic charge preceding the lightning bolt, but only when the bolt actually strikes. What does this phenomenon indicate about voltage, current, and magnetism?
In 1820, the French physicist André Marie Ampère discovered that two parallel wires carrying electrical current would either be attracted to one another, or repelled by one another, depending on what directions the two currents were going. Devise an experiment to reproduce Ampère’s results, and determine which directions current must go to produce an attractive versus a repulsive force.
A permanent magnet is a device that retains a magnetic field without need for a power source. Though many of us have experienced the effects of magnetism from a permanent magnet, very few people can describe what causes permanent magnetism. Explain the cause of permanent magnetism, in your own words.
Cranes used to move scrap iron and steel use electrically powered magnets to hold the metal pieces, rather than a scoop or some other mechanical grasping device:
In this illustration of a crane, superimpose a drawing showing the electromagnet, electrical power supply and wiring necessary for this to work. Also include a switch so the crane operator can turn the magnet on and off. Also, draw an electrical schematic diagram of the same circuit, showing all components in the crane’s magnet circuit.
A solenoid valve uses magnetism from an electromagnet coil to actuate a valve mechanism:
Essentially, this is an electrically-controlled on/off water valve. In the development of this valve, though, the design engineers discover that the magnetic force produced by the electromagnet coil is not strong enough to achieve reliable valve actuation every time. What can be changed in this solenoid valve design to produce a greater actuating force?
A coil of wire is formed of many loops. These loops, though tracing a circular path, may be thought of as being parallel to each other. We know that whenever two parallel wires carry an electric current, there will be a mechanical force generated between those two wires (as in André Marie Ampère’s famous experiment).
When electric current is passed through a coil of wire, does the inter-loop force tend to compress the coil or extend it? Explain your answer.
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