Simple circuit question?

[mr chievous]

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Here is a picture of a super simple circuit. The voltage drop across the resistor is 12 volts. If the voltage drop across the resistor is 12 volts, then what moves the electrons from point B to point D? I think I'm not understanding something properly 🙁

 

[Captain Sisko]

Here is a picture of a super simple circuit. The voltage drop across the resistor is 12 volts. If the voltage drop across the resistor is 12 volts, then what moves the electrons from point B to point D? I think I'm not understanding something properly 🙁

In reality the voltage drop across the resistor is slightly less than 12 v because the wire has a very small resistance of its own. To simplify things we assume that this resistance is zero and no voltage difference is required to push the electrons through a wire. But yes, there is actually a small resistance and voltage difference there. So what you'd do is add up the resistance of your wire, resistor, and wire back to the battery as if they were resistors in series, determine the current and then use that to find the voltage drop in each wire

Pro- tip: resistance in a wire is a function of cross sectional area, length, and material conductivity.

 

[AmirTimur]

Here is a picture of a super simple circuit. The voltage drop across the resistor is 12 volts. If the voltage drop across the resistor is 12 volts, then what moves the electrons from point B to point D? I think I'm not understanding something properly 🙁

I'm not an expert in this, but I think your understanding of circuit is infected with a misconception. Flowery language aside, an electron doesn't actually "travel" from point B to point D. What happens when you turn on the switch, is that every single electron in a wire starts marching, b/c it's affected by the electric field generated by the battery. This electron drift speed (e.g. marching electrons) is extremely slow (a fraction of a meter per second or something like that). Hence, it's not like a charge started out in the battery, started marching and then it's energy was dissipated by the resistor. No. Electron drift flow is continuous throughout the wire, and that energy is harnessed by the resistor (presumably into a useful form of energy).

Read this for more info: http://www.physicsclassroom.com/Class/circuits/u9l2c.cfm