*Experiments with magnets and our surroundings*

**Twelve Fundamentals of Magnetism**

**11. Transformer Action**

**a. Links for this topic**

http://en.wikipedia.org/wiki/Electromagnetic_induction

https://en.wikipedia.org/wiki/Transformer

A voltage can be induced within a wire if it experiences a changing magnetic field.

This can be considered a Transformer Action since this is how transformers operate.

**c. When was this discovered?**

This phenomenon was discovered by Michael Faraday in 1831 and Joseph Henry in 1832, independently of each other.

**d. How much voltage is induced?**

The magnitude of the induced voltage, Ei = N*dΦ/dt

Where:

i. Ei is the induced voltage, Volts

ii. N is the number of turns of wire seeing the changing magnetic field

iii. dΦ is the change in the magnetic field, Wb

iv. dt is the change in time, sec

A very simple equation! The voltage induced is only affected by the the number of turns of wire, and how fast the magnetic field is changing.

**e. What if the field is changing sinusoidally?**

Since the voltage
generated by the utility is sinusoidal in shape, how does this affect the above
equation?

The rms value of the induced voltage, Erms
= 4.44*f*N*Φmax
for a sinusoidally changing flux

Where:

i. Erms is
the rms value of the induce voltage

ii. 4.44 is
derived from 2*pi/sqrt(2)

iii. f is the
frequency of the flux, Hz

iv. N is the
number of turns of wire around an iron core

v. Φmax
is the maximum or peak value of the flux that is changing in a sinusoidal
fashion, which is the same as Bmax*Ac

1. Bmax is the maximum or peak value of the flux density, Tesla

2. Ac is the area of the iron core, meter^{2}

Note that the current in the secondary circuit will create a magnetic flux that opposes the magnetic flux created by the current in the primary circuit.