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  • Suppose we take our circuit of a battery and a light bulb,

  • and we make it slightly more complicated by adding a switch.

  • When the switch opens, the charged particles are prevented from passing through.

  • Particles with the same charge repel one another,

  • and they therefore spread out throughout the wire.

  • The events shown here all happen at the same time, and this is the result.

  • For the light bulb to turn on, the switch must close, so as to create

  • a complete path for the charged particles to flow around the loop.

  • If we have several light bulbs, each light bulb can have its own individual switch.

  • Or, we can have one switch which controls all the light bulbs.

  • The number of charged particles that pass by each second

  • is what we refer to as the current.

  • The charged particles flow through the light bulb because

  • the battery causes them to have a higher potential energy

  • on one side of the light bulb than the other.

  • This potential energy is what we refer to as voltage.

  • If both sides of a light bulb are at the same voltage,

  • then no current will pass through it.

  • As the voltage across the light bulb increases,

  • the amount of current through the light bulb also increases,

  • and the light bulb produces more light.

  • When a switch closes, it causes the two different parts

  • of a circuit that it connects to be at the same voltage.

  • If both sides of a light bulb are at the same voltage,

  • then no current will pass through it.

  • And if no current passes through a light bulb,

  • then this means that both sides of the bulb are at the same voltage.

  • A properly working battery ensures that the difference

  • in voltage across it is always at a specific value.

  • All points that are directly connected to each other through

  • metal conductors and closed switches are at the same voltage.

  • This means that if we have several light bulbs connected

  • to a battery in parallel, the voltage across each light bulb

  • is equal to the voltage that is produced by the battery.

  • Since the voltage across the light bulb determines how much

  • current passes through it, each of these light bulbs will have

  • the same current pass through it as we had when we just had

  • one light bulb connected to the battery.

  • The total current drawn from the battery is the sum

  • of all the currents drawn by each of the light bulbs.

  • Now, let us consider a situation where we have

  • several light bulbs connected in series.

  • Since the total voltage across the group of light bulbs is at

  • the specific value set by the battery, the drop in voltage

  • across each light bulb is only a fraction of this.

  • Since the current that passes through each light bulb

  • depends on the voltage across it,

  • this smaller voltage across each of the light bulbs means

  • that a smaller current will flow through them.

  • This means that the lights will not be as bright.

  • Because the light bulbs are connected in series,

  • this means that the current passing through each of them is the same.

  • The amount of current entering always has to

  • be equal to the amount of current exiting.

  • This is what we refer to as Kirchhoff's Current Law.

  • This is accompanied by another law, called Kirchhoff's Voltage Law,

  • which states that as we travel around a loop,

  • the amount of voltage increases that we experience

  • must be exactly equal to the amount of

  • voltage drops that we experience.

  • The use of these two laws together allows to analyze all electric circuits,

  • no matter how complex they become.

  • Much more detailed information about

  • voltage, current, and electric circuits

  • is available in the other videos on this channel.

Suppose we take our circuit of a battery and a light bulb,

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B1 US voltage bulb light bulb current battery switch

Electric Circuits - Basics of the voltage and current laws

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    Amy.Lin posted on 2021/01/06
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