- #1

mcairtime

- 9

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Hello,

I am wondering why such a large voltage can be generated when the switch in a circuit containing an inductor is opened. The following is from a set of Electromagnetism course notes:

"

I have worked through the mathematics of calculating the emf generated both when the switch is first closed (equal to the emf of the supply) and when the switch is opened, when it can take more or less any value you want by tweaking the values of the resistance of the neon lamp etc. However, I feel like I still do not understand the situation in a fundamental way i.e. in terms of the rate of change of magnetic flux linkage.

If the emf generated in the inductor is 1.5 V when the switch is closed and over 80 V when it is opened then the rate of change of magnetic flux linkage in the inductor must be much greater when it is open. Why is this the case?

Hope it's clear what I'm after but feel free to seek clarification if needs be of course.

Many thanks in advance.

I am wondering why such a large voltage can be generated when the switch in a circuit containing an inductor is opened. The following is from a set of Electromagnetism course notes:

"

*The 1.5 V supply in the circuit below is insufficient to light the neon lamp. A neon lamp needs about 80 V across it before it will light.*

http://file:///C:/Users/CPTEMP~1/AppData/Local/Temp/msohtmlclip1/01/clip_image002.jpg The switch is closed and the current builds up to its maximum value. When the switch is opened, the current rapidly falls to zero. The magnetic field through the inductor collapses (changes) to zero producing a very large induced e.m.f. for a short time. The lamp will flash."http://file:///C:/Users/CPTEMP~1/AppData/Local/Temp/msohtmlclip1/01/clip_image002.jpg The switch is closed and the current builds up to its maximum value. When the switch is opened, the current rapidly falls to zero. The magnetic field through the inductor collapses (changes) to zero producing a very large induced e.m.f. for a short time. The lamp will flash.

I have worked through the mathematics of calculating the emf generated both when the switch is first closed (equal to the emf of the supply) and when the switch is opened, when it can take more or less any value you want by tweaking the values of the resistance of the neon lamp etc. However, I feel like I still do not understand the situation in a fundamental way i.e. in terms of the rate of change of magnetic flux linkage.

If the emf generated in the inductor is 1.5 V when the switch is closed and over 80 V when it is opened then the rate of change of magnetic flux linkage in the inductor must be much greater when it is open. Why is this the case?

Hope it's clear what I'm after but feel free to seek clarification if needs be of course.

Many thanks in advance.

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