Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

I was informed that in a circuit, the current will stay the same, and this is why the lightbulbs will light up (because in order for the current to stay the same, the drift speed of the electrons need to get faster). However, I do not understand why the current needs to stay the same from point to point.

Why does the current stay the same from point to point in a circuit?

share|improve this question
5  
When you sya "the current will stay the same," do you mean that it's the same from moment to moment (ie, constant in time), or that it's the same from point to point along the current? –  Colin McFaul Feb 22 '13 at 3:40
    
welcome to physics.SE . I have given you a +1 so you can start accumulating some reputation that will allow you to comment. You can edit your question using the "edit" link above so as to clarify what Colin asked you.. –  anna v Feb 22 '13 at 8:07
    
Sounds like chapter 19 of the third edition of Matter & Interactions by Chabay and Sherwood. It also sounds like you haven't read the chapter, because your question is addressed very early on in the reading material. Read it again VERY carefully, remembering that fundamentally, current is counting electrons drifting past a given point in a one second duration. –  user11266 Mar 10 '13 at 22:55
add comment

2 Answers

The current doesn't necessarily remain constant in time in a circuit. For a simple example, consider a so-called $LC$-circuit. In this circuit consisting of an inductor and a capacitor in series, the current oscillates with angular frequency $$ \omega = \frac{1}{\sqrt{LC}} $$ were $L$ is the inductance of the inductor, and $C$ is the capacitance of the capacitor. In fact, the $LC$-circuit is a simple example of a more general class of circuits called AC or "alternating current" circuits where the current is a periodically changing function of time.

Having said this, there are many circuits in which the current doesn't change much once the system is in the steady state. A circuit consisting of a lightbulb (which is basically just a resistor) connected in series to a battery is a simple example. In this case the current $I$ satisfied Ohm's law and is given by $$ I = \frac{V}{R} $$ where $V$ is the voltage of the battery and $R$ is the resistance of the bulb.

share|improve this answer
add comment

Electrons are present everywhere in an electric circuit. When a potential difference is applied to the circuit, an electric field is set up throughout the circuit, almost with the speed of light. Electrons in every part of the circuit begin to drift under the influence of this electric field and a current begins to flow in the circuit immediately.

You have to note here that if the potential difference you're applying is constant as with a D.C battery the electric field remains constant, and thus the current remains constant.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.