Light bulb ignition
Take 10 minutes to prepare this exercise.
Then, if you lack ideas to begin, look at the given clue and start searching for the solution.
A detailed solution is then proposed to you.
If you have more questions, feel free to ask them on the forum.
A plane coil of square-section of side
is put near a high voltage wire, travelled by the effective intensity
.
Its frequency is
.
A light-bulb is added to one end of the coil and can only be turned on for a voltage
.
Question
How many whorls are necessary for the light to turn on ?
Can you explain why the light can turn on ?
Think about Faraday's law.
The magnetic field created by the wire is : (Use Ampere's circuital law)
The flux of this field through the coil is :
Faraday's law gives the electromotive force that appears in the frame :
The effective voltage at the edges of the light bulb is :
Hence the minimum number of whorls in the coil can be deduced from the formula :
