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: why sparks are producing while switch on

Wednesday, August 18, 2010
Asked by:shyamlal
Subject*:about electricity
Question*:why sparks are producing while switch on
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posted by S @ 8:47 PM  
  • At April 22, 2011 at 10:35 AM, Anonymous Anonymous said…

    Spikes, when disconnecting a wire or fliping off a switch, are created because of the inductive property of the circuits.

    In an inductor (or inductive circuit), the currect can not change instently. This is the opposite of a capacitor (or capacitive circuit) where the voltage can not change instently.

    So, imagine a circuit where you have current flowing and you disconnect the wire. At the moment the wire is disconnected (or the switch is flipped off), some current will continue to flow in the wire for a brief moment. Since there is no power source feeding the circuit, but that electrons continue to flow, the lead of the wire you disconnect, or the pole of the switch you turn off, will get at a very high voltage (can be in the order of a few thousands volts depending on the current and the inductance of the curcuit). It is this voltage that create a spark. The bigger the current and inductance, the bigger the spark. For example, unpluging a big motor while it's running can fuse the connector leads.

    This effect is also present in relays and in switching power-supply (to name a few) and have to be taken into account (or else, the relay of power supply would be destroyed). In this case though, a diode is used to limit the voltage to safe level (and let the current loop through the diode when the circuit is open).


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