Current Flow Through Circuit

In summary: V power supply and a 1 ohm resistor, the current flows identically through all points in the wire when the circuit is closed, or if there is a delay due to the speed of light. He uses the analogy of filling a hose with water, and wonders if the water will instantly start flowing through the other end when the supply is opened, or if there will be a delay due to the elasticity of the hose. There is no clear answer to this question, as it depends on various factors such as capacitance and inductance. However, it is important to note that electrons do not travel at the speed of light, and there is a finite speed at which
  • #1
Scott Pratz
10
0
I have a simple series circuit, with a 9V power supply, and a 1 ohm resistor. If I place to identical fuses in series on opposite sides of the resistor that are rated for <9A, which fuse will blow first?

I am essentially asking if current flows identically through all points in a wire the instant the circuit is closed, or if there is an instant at "the speed of light (electrons)" where current flows only in the high electron side of the wire.

Basically I'm thinking (if I revert to the water metaphor), there is a hose and I can either open the supply to with it empty hose that needs to have water passed through it, or I canopen it with an already filled hose which will instantly start passing water though the free end.

Hopefully this isn't too vague..
 
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  • #2
I have two "identical" ice creams. If I take them out of a fridge at same time, which one totally melts first?
 
  • #3
I too can answer questions with metaphors that have absolutely no evidence... provide any?
 
  • #4
If same current passes through both "identical" fuses, they should melt at same instant of time (in theory). However, in the real world you'll never have two identical fuses placed in identical enviroment.
 
  • #5
Scott Pratz said:
I am essentially asking if current flows identically through all points in a wire the instant the circuit is closed, or if there is an instant at "the speed of light (electrons)" where current flows only in the high electron side of the wire.

That question is clearer than the question about the resistors! It's not clear how much you reality that you want to allow in the question about the resistors.

My answer is: yes, the change in the electric field propagates through the wire at a finite speed. This finite speed is not necessarily the speed of light in a vacuum. Viewing the electrons as classical particles, they have a mass. They don't instantly accelerate when acted upon by a force, so it isn't the electrons themselves that move at the speed of light. There are still a lot of undefined aspects to the above question, so I'm sure other people might not agree.
 
  • #6
The water analogy can be useful but one must be rigorous.

Your "full" hose cannot transmit pressure instantaneously to its other end because it is elastic and will swell slightly under the higher pressure. So you must add water to the hose to start the pressure rise propagating down the hose to accelerate the water.
But you'd be hard pressed to measure that delay with a stopwatch.
That compliance in your garden hose is analogous to capacitance. Inertia of the water is analogous to inductance. Interestingly c is a function of capacitive and inductive related parameters permittivity εο and permeability μο .
http://en.wikipedia.org/wiki/Vacuum_permittivity

Here's a link that'll make you scratch your head:
http://amasci.com/tesla/tmistk.htmlhave fun.
 
  • #7
Scott Pratz said:
I am essentially asking if current flows identically through all points in a wire the instant the circuit is closed, or if there is an instant at "the speed of light (electrons)" where current flows only in the high electron side of the wire.

electrons DONT travel at the speed of light, google electron drift :)

Dave
 

What is current flow through a circuit?

Current flow through a circuit refers to the movement of electric charge through a closed path or circuit. It is measured in units of amperes (A) and is caused by the flow of electrons.

How is current flow through a circuit related to voltage and resistance?

According to Ohm's Law, current flow (I) is directly proportional to voltage (V) and inversely proportional to resistance (R). This means that as voltage increases, current flow increases, and as resistance increases, current flow decreases.

What factors affect the flow of current through a circuit?

The flow of current through a circuit is affected by the voltage source, the resistance of the circuit, and the type of conductor material used. Other factors such as temperature, length, and cross-sectional area of the conductor can also impact current flow.

How is current flow measured in a circuit?

Current flow is measured using a device called an ammeter. It is connected in series with the circuit and measures the amount of current passing through a specific point in the circuit.

What are the different types of current flow in a circuit?

The two main types of current flow in a circuit are direct current (DC) and alternating current (AC). DC flows in one direction, while AC alternates between flowing in opposite directions. AC is the type of current used in most household and industrial circuits.

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