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An inductor resists a change in current. If you have a steady state current going through an inductor and you attempt to suddenly increase the current, the inductor will nearly instantaneously present a higher resistance so that the current does not immediately change. Its resistance, then, will start to decrease as the current ramps up to the new value.

Similarly, if you have a steady state current going through an inductor and you attempt to suddenly decrease the current, the inductor will nearly instantaneously present a lower resistance so that the current does not immediately change. Its resistance, then, will start to increase as the current ramps down to the new value.

That's all just background information so you can understand what an inductor is.

If you have a steady state current going through an inductor and you attempt to suddenly decrease the current to zero by opening the circuit, the inductor will respond by attempting to maintain the current, but that current has nowhere to go. This creates a large negative voltage spike across the inductor. Think about it. Ohm's law says that voltage is current times resistance. You have some current; you have infinite resistance; therefore you must have infinite voltage. In fact, a theoretical pure inductor will do exactly that - generate an infinitely large negative voltage spike. That does not happen in practice, but it is very common to see transients of several hundred or thousand volts. This is why you need to have some kind of suppression circuit in place - otherwise that transient will go back and blow out whatever circuit is driving it.

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โˆ™ 2011-03-25 14:21:22
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Q: Why does a switch spark when disconnecting a coil carrying high dc current?
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Why is an arc or spark produced when an inductive load is switched off?

when inductive load is switched off then current decreases as a result emf induced in the inductor or as whole of the circuit. There is air between switch and circuit wire. Emf tends to jump from higher pd to lower pd so air become ionised and spark is prouced


How does oil circuit breaker work?

The switch contacts are immersed in oil to quench any spark that might occur when the current is interrupted. Water can't be used because it makes things rusty and is not a good insulator unless highly pure.


What could go wrong if you change the voltage on a PC power supply?

the computer will not switch on. May be the SMPS fail leading to a huge spark.


Why do you have to switch off any devices before you unplug them?

You have to switch off any devices before you unplug them because there is often a spark as you withdraw the plug, so the plug and socket materials are gradually eroded and damaged. Switches are designed with contact materials and shapes that withstand this erosion better and are spring-loaded to snap open to minimize the time when arcing can occur. As the current to a circuit is interrupted, at first the air gap is less than a micrometer, aka a micron. The breakdown voltage for a micron of air is less than a volt, after which that micron of air is a conductor, and each additional micron of air then breaks down and so on. The spark is destructive because it concentrates the current flow on a tiny area causing micro-scale melting and metal migration. In countries which use a 60 Hz AC electric power service, the spark is extinguished 120 times a second as the voltage waveform passes through 0V (zero volts). The spark doesn't always happen, because sometimes the voltage is close to 0V when the circuit is interrupted.


Why do you get a shock current when pushing a trolley?

There must have been a build up of static electricity, either in yourself or in the trolley. The shock is the spark as it makes its way to earth.

Related questions

How does kill switch work on car?

The kill switch interupts the spark to the spark plug and stops the eingine.


How do you replace spark plug Ford Explorer?

The spark plugs on a Ford Explorer are replaced by first disconnecting the battery. Remove the spark plug using a spark plug socket. Replace with the factory recommended spark plug.


Polaris sportsman 700 2001 starts then wont start no spark?

try disconnecting gauge cluster


Where is the kill switch on a mini bike?

near the spark plug. some engines have lever that touch the spark plug ,others have a grounded switch


Why does the magnetization current impose on upper limit on the voltage applied to a transformer core?

The magnetization current imposes an upper limit on the voltage applied to a transformer core due to the ability of the respective spark gap to extinguish. If too much current supply is available the spark gap becomes overheated. This makes it unable to "switch-off" when the high or elevated supply current is flowing through it.


Why does the magnetization current impose an upper limit on the voltage applied to a transformer?

The magnetization current imposes an upper limit on the voltage applied to a transformer core due to the ability of the respective spark gap to extinguish. If too much current supply is available the spark gap becomes overheated. This makes it unable to "switch-off" when the high or elevated supply current is flowing through it.


Why does the magnetization current impose an upper limit on the voltage applied to a transformer core?

The magnetization current imposes an upper limit on the voltage applied to a transformer core due to the ability of the respective spark gap to extinguish. If too much current supply is available the spark gap becomes overheated. This makes it unable to "switch-off" when the high or elevated supply current is flowing through it.


Should their be a spark inside a light switch when it's turned on?

If you are seeing a spark then the switch should be changed out right away. The spark is created by bad contacts within the switch its self. These bad contacts will create heat and eventually destroy the switch. Make sure that the rating of the switch is greater than the load that is connected to it. The only time a switch might draw an arc is when it is opened but it should never arc when closing. Yes there should be a spark when a switch is put on.


What current does a spark plug receive?

It uses DC current.


What are the release dates for The Switch and the Spark - 2007?

The Switch and the Spark - 2007 was released on: USA: 23 June 2007 (San Francisco Bay Area)


How do you change spark plugs on a 2003 explorer 4.6?

It is important to replace car parts after so many miles. Spark plugs are changed by disconnecting the batteries, the spark plug cables, removing the spark plugs, replace them with new spark plugs, reconnecting the cables, and the car battery.


My snow blower has no spark. Why?

Either your coil is shot or your kill switch is stuck closed. If you warm it up (above freezing) and it still doesn't have spark, bet on the coil being bad or if you are lucky, the sparkplug wire is cracked and grounded. you can isolate & test the coil by removing the engine shroud, you will find one thin green or black wire going into the back of your coil, disconnecting this wire will isolate the coil from the rest of electrical system. recheck spark with the wire disconnected, if you still dont have spark you need a new coil, if now have spark it means your coil is working and either a switch or a bad wire is grounding the system.

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