When the battery terminals of the flashlight are briefly connected and turned off, we notice a spark. It is much stronger if an electromagnet is connected to the battery. Why?

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Libby Weaver · Accepted Answer

When you connect and disconnect the flashlight from the battery terminals the arc is due to the fact that the contacting surfaces are not perfectly flat. A microscopic view would show surface irregularities. The current density at the points of contact is greater than the average current density over the entire contacting surfaces. It is at these points of contact where the arcing is occurring when making and breaking the circuit. This is why mechanical switches always produce some arcing when making and breaking a circuit. The switch contacts are never perfectly flat.Now if in addition you add the inductor the arcing is greater because, once again, an inductor resists a change in current. The first equation tells you if you attempt to quickly disrupt the current in and inductor (a high value of   d  i      /    d  t), it induces a large voltage. The greater intensity arc is due to the large induced voltage, in additio

When the battery terminals of the flashlight are briefly connected and turned off, we notice a spark. It is much stronger if an electromagnet is connected to the battery. Why?

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