2012 Common Reading Program
The Electrical Engineering in The Boy Who Harnessed the Wind
In the 2012-2013 Purdue common reading selection, The Boy Who Harnessed the Wind, William Kamkwamba built a windmill that used electromagnetic induction to convert a mechanical rotation into an electric current that he used to power electrical devices such as radios and light bulbs.
In 1831, Michael Faraday, in London, and Joseph Henry, in New York, independently discovered electromagnetic induction. The equation that describes electromagnetic induction is referred to as Faraday's Law and is one of the four fundamental equations of electromagnetics referred to as "Maxwell's Equations." (Actually Maxwell worked with 20 equations and never saw the formulation that today is referred to as Maxwell's Equations, this formulation being due to Oliver Heaviside after Maxwell's death.)
A very simple experiment, as shown in the following link "Electromagnetic Induction," can demonstrate electromagnetic induction. In the video a wire is formed into a coil of diameter 3 cm. The ends of the coil are attached to an ammeter, which is a device that measures the amount of current flowing in the coil. Current is a flow of electric charge and in the coil a current would be a flow of electrons.
There is no current with just the coil attached to the ammeter. However, if there is a changing magnetic flux inside the coil, the ammeter shows there is a current flowing. This is electromagnetic induction. In the video the mechanical movement of the permanent magnet is converted into an electric current.
In a windmill, such as the one William Kamkwamba built, the changing magnetic flux is obtained by rotating a coil in a fixed magnetic field. So for half the rotation the magnetic field is increasing and for half the rotation the magnetic field is decreasing in the coil. The result will be an alternating current, a simple AC generator. The following link explains and demonstrates a simple AC generator.
The circuit breaker that William constructed for the wiring in his house included electromagnets. The following video describes and demonstrates an electromagnet.
William talked about extracting electric motors from cassette players and using them in reverse as electric generators. To understand how an electric motor works, first look at this demonstration of how a current carrying coil generates a magnetic field and acts similarly to a bar magnet.
Magnetic Field from a Current Carrying Coil
So two coils with current flowing will act as two bar magnets. If the two coils are facing each other, they will either be attracted together if the currents are flowing in the same direction, or repelled from each other if the currents are flowing in opposite directions.
Force between current carrying coils
Now that we understand how a current carrying coil acts as a magnet, the final concept on how a rotary motor works is that a current-carrying coil placed in a fixed magnet field will rotate, it will experience a torque, until the magnetic field of the coil is aligned to the fixed external magnetic field. Here is a demonstration of a simple motor where a permanent magnet is the source of the fixed external magnetic field.
Simple Motor with a Permanent Magnet
A current carrying coil can also be the source of the fixed external magnetic field as demonstrated with the following simple motor.
Simple Motor with an Electromagnet
The story of Michael Faraday, discoverer of electromagnetic induction, the concept used by William Kamkwamba in his windmill, is inspiring like William's. Faraday was born into a very class-based English society and had no chance of getting a formal education, let alone becoming a scientist.
So Faraday had to find a trade. He apprenticed with a bookbinder and read every book he was tasked to bind. Faraday especially enjoyed the books about science and the bookbinder allowed Faraday to set up and perform some of the experiments he read about.
In those days scientists were celebrities and would give lectures to the public. The tickets to these lectures were expensive, but a client of the bookbinder gave Michael Faraday a ticket to a lecture by a famous chemist, Humphry Davy.
Faraday managed to get tickets to more Davy lectures and took extensive notes during the lectures. Faraday then bound all his notes and sent them to Davy. Davy was impressed, but that could have been the end except Davy had an accident in the lab and injured his eyes. He immediately thought of Faraday to be his note taker.
Faraday left his apprenticeship to the bookbinder and went to work as Davy's lab secretary. Faraday progressed to helping with experiments and eventually surpassed Davy in experimental ability. Upon Davy's retirement, Faraday became the head of the Royal Institution in London. Faraday made many great discoveries besides electromagnetic induction and he is considered one of the greatest experimentalists of all time.
Faraday was ahead of his time in many ways. He was an environmentalist writing letters to the London newspapers about the polluted condition of the River Thames. He instituted the "Children Christmas Lectures" at the Royal Institution, which still go on today, to encourage an interest in science.
Humphry Davy made many great scientific discoveries, but his greatest discovery was Michael Faraday.
The following are some additional demonstrations of electromagnetic concepts
Rotary Electrostatic Motor
Van de Graaff generator
force on a moving charge in a magnetic field
Force on a current carrying straight wire in a magnetic field
Force on a Current Carrying Wire in a Magnetic Field
Magnetic field of a bar magnet
Demonstration of Diamagnetism & Paramagnetism
Eddy Currents and Magnetic Braking of a Pendulum
Styrofoam Cup Loudspeaker
Youngs Double Slit Experiment
Refraction and Total Internal Reflection