Propagation sequencing in series circuit?

In summary, the question posed at Mythbusters was about the propagation of current from a switch that is a long distance from a DC power source. This was tested with two 1 mile long wires connected to the positive and negative terminals of the power source, respectively, with an open switch and DC LEDs in series. After the switch is closed, the potential at the switch results in immediate current flow at the switch, propagating back via both wires to the battery and causing the LEDs to light up in sequence. The current travels at a much slower pace than the electromagnetic fields around the wire, but changes in current propagate at the same speed as the fields. The electrical engineering experts at Mythbusters were able to measure when an LED turned on, but
  • #1
rcgldr
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This came up at mythbusters, a question about the propragation of currrent from a switch that is a long distance from a DC power source. Assume the wires are sufficiently large (capcitance wise):

1 mile long wire connected to positive terminal of DC power source at one end, open switch at other end, with DC LEDs in series as part of the wire

1 mile long wire connected to negative terminal of the same DC power source as above at one end, to the same open switch as above at other end, with DC LEDs in series as part of the wire.

Assume that the state of the system has stabilized, and an idealized DC power source. The postive side of the switch has positive potential (insufficient electrons), the negative side of the switch has negative potential (excess electrons). Now close the switch.

Does the potential at the switch result in immediate current flow at the switch, propagating back via both wires to the battery, so that the LEDs light up in sequence at the rate of propagation?
 
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  • #2
As you might know, the current don't travel very fast in a wire, but the electromagnetic fields around the wire move near light speed. When the fields change in some part of the wire, the local current changes. So the electrons don't move very fast, but the local current changes do. These changes in current propagate just as fast down a wire as the surrounding fields.

Anyway, if the two legs of the loop are isolated from one another, so that their fields don't overlap much, a signal propagates down both wires, originating at the switch, back to the battery.

How did the electrical engineering geniuses at Mythbusters manage to measure when an LED turned on?
 
  • #3
Phrak said:
How did the electrical engineering geniuses at Mythbusters manage to measure when an LED turned on?
They didn't it was just an abstract exercise.
 
  • #4
I wonder how sharp an edge one could get out of closing a mechanical switch. Compared to the speed of light, it happens very very slowly. Then, some current will flow before contact, as the capacitance of the switch decrease before the current punctures the dialectric, or whatever it is that happens.
 

Related to Propagation sequencing in series circuit?

What is propagation sequencing in series circuit?

Propagation sequencing in series circuit refers to the process of analyzing and understanding the flow of electrical energy through a circuit that is connected in a series. This includes understanding the direction of current flow, voltage drops, and the total resistance of the circuit.

How is propagation sequencing different from regular sequencing?

Propagation sequencing specifically focuses on series circuits, where the components are connected in a single path. This is different from regular sequencing, which can refer to the order of events or processes in a broader context.

Why is propagation sequencing important in circuit analysis?

Propagation sequencing is important in circuit analysis because it allows us to understand the behavior of a series circuit and determine the voltage and current at different points in the circuit. This information is crucial in troubleshooting and designing circuits.

What are the key components of propagation sequencing?

The key components of propagation sequencing in series circuits include the voltage source, resistors, and the connections between them. It also involves understanding the direction of current flow and the total resistance of the circuit.

How can I apply propagation sequencing in series circuits to real-life situations?

Propagation sequencing in series circuits can be applied in various real-life situations, such as analyzing the flow of electricity in household circuits, understanding the operation of electronic devices, and troubleshooting electrical issues in cars or other machinery.

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