18 lines
1.3 KiB
Markdown
18 lines
1.3 KiB
Markdown
# Back EMF
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**back electromotive force**
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The Back EMF is the voltage across an inductor, it is proportional to the change of current flowin through an inductor.
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It is caused by a changing magnetic field around the inductor, which itself is caused by a change in the current flowing through it.
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### Example:
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After switch on (A $\rightarrow$ B) we see that the voltage spikes immediately, this causes the magnetic field to change rapidly, which creates a oppositional polarity, which causes a huge resistance to current flow, so the current flowing at the start is almot zero. As soon as the voltage begins to drop, the back emf becomes weaker and current is allowed to flow.
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After switch on (B $\rightarrow$ C) the magnetic field around the inductor collapses, which causes a back emf in to the inductor. And because the change in the strength of the magnetic field is opposite to switch on, the induced voltage across the inductor is opposite to the one on switch on. This Back EMF can cause very large spikes in voltage, because the voltage induced across the inductor is dependent on the rate of change the strength of the magentic field.
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For some circuits this large spikes in voltage can cause problems, as the voltage may be high enough to jump switches (arcing) or damage semiconductors. |