# Basic Electromagnetism and Electromagnetic Induction

## Basic Electricity

• #### Question 1

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?

• #### Question 2

Just as electricity may be harnessed to produce magnetism, magnetism may also be harnessed to produce electricity. The latter process is known as electromagnetic induction. Design a simple experiment to explore the phenomenon of electromagnetic induction.

• #### Question 3

A large audio speaker may serve to demonstrate both the principles of electromagnetism and of electromagnetic induction. Explain how this may be done.

• #### Question 4

What do you think might happen if someone were to gently tap on the cone of one of these speakers? What would the other speaker do? In terms of electromagnetism and electromagnetic induction, explain what is happening.

• #### Question 5

Draw the pattern of the magnetic field produced by electric current through a straight wire and through a wire coil:

Explain your answer using either the right-hand rule (conventional flow) or the left-hand rule (electron flow).

• #### Question 6

When engineers and physicists draw pictures illustrating the magnetic field produced by a straight current-carrying wire, they usually do so using this notation:

Explain what the circle-and-dot and circle-and-cross symbols mean, with reference to the right-hand rule.

• #### Question 7

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.

• #### Question 8

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.

• #### Question 9

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.

• #### Question 10

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?

• #### Question 11

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.