Introduction to Faraday’s law and electromagnetism

Before we start learning this law and electromagnetism, we have to become familiar with the general relationships that exist between electricity and magnetism as follows:

1. Electric current flow will always produce some form of magnetism.
2. Magnetism is by far the most commonly used means for producing or using electricity.
3. The peculiar behavior of electricity under certain conditions is caused by magnetic influences.

Faraday’s Law states that changing magnetic fluxes through coiled wires generate electricity (currents and voltage). In other words, the induced electricity is proportional to the change in magnetic flux, so the greater the change is the more electricity generated. A cupper coil and moving magnet are commonly used to explain the law as shown below.

As the magnet moves back and forth, electricity is being generated because of the following reasons.

1. A change in magnetic flux. Magnetic flux is a measurement of the strength of the magnetic field, which is calculated by multiplying the average of magnetic field B by the area A it goes through. Given by this equation Φ= B.A and the unit used is the Maxwell.
2. Whenever we have a change in magnetic flux, we’ll generate an electromotive force (emf) that will create a current going through the coil. This induced current is going through the coil in a direction to minimize the change in the magnetic flux. The way to look at it mathematically is by the following equation.

emf= – the change in Φ/ the change in time. where the negative sign by Lenz law indicates that emf will oppose the change in Φ.

Experiment and procedure

In the lab, we used a generator that works just like the picture above. And by connecting it to a voltage probe to the NXT, we could calculate the voltage output of the generator using Excel sheet. Simply, our experiment was to correlate the number of shakes of the generator, in a thirty second time interval, with the voltages (or more precisely the sum of the square of the voltages) that the generator generates. Now, we did five runs with different number of shakes. We proved that the more shakes the greater the voltage output. In other words, for the induced voltage to be increased, the change in magnetic flux (Φ) has to be increased too. For our experiment, time seemed to play no role, because for each run we had the same time interval (30 s). Below is a graph showing the relationship between the voltage output and the number of shakes.

It is obvious that the more shakes we do the more electricity generated.

Conclusion

This Faraday’s law is very important and helped with a number of applications. For instance, musical instruments. Musical instruments like electric guitar, electric violin etc have a pick-up device attached to them. It consists of a fine enameled copper wire wound on a magnet. When the metal strings of the guitar are strung, the vibrating string cuts the magnetic flux of magnet linking the coil due to which electric current is induced in the pick-up’s coil. It is modulated by the mechanical vibrations of the strings. This electrical signal is then amplified and recorded by suitable devices. In addition the phenomena of electromagnetic induction is also used in instruments and machines like Induction motors, Induction Sealing, Audio video tapes, Hall effect meters, Faraday Disk etc.

http://www.youtube.com/watch?v=qWu82nJS42I

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Basic Electricity prepared by the Bureau of Naval Personnel.