# Why is current not 0 in a regular resistor - battery circuit immediately after you closed a circuit?

In regular open circuits with either a capacitor or inductor element, (when capacitor is uncharged) with a battery, when a switch is closed to complete the circuit the current is said to be 0 because current doesn't jump immediately.

But in a circuit with just resistors, as soon as a switch is closed the current isn't 0?

Example is this question from 2008 AP Physics C Exam

http://apcentral.collegeboard.com/apc/public/repository/ap08_physics_c_em_frq.pdf

Go to Question 2 for details.

• It's not clear enough what you're having trouble with. Conceptually, yes, current jumps instantly in a battery-resistor circuit. If it is as simple as this, I don't see what you're asking. Aug 27 '12 at 19:29
• @AlanSE, that's my problem why does it jumpy instantaneously?
– Hawk
Aug 27 '12 at 20:12
• @jak, it's as simple as Ohm's Law. When the switch is instantaneously closed, the voltage across the resistor instantaneously changes from zero to some non-zero value. Thus, by Ohm's Law, the current instantaneously changes from zero to some non-zero value. Aug 28 '12 at 1:56

The answer is as above, the current does not instantaneously propogate throughout the circuit but at some finite speed $<c$. In introductory problems however this speed is much faster than you need to worry about.
This is really a footnote to user1631's answer: even in the absence of any inductance the current obviously can't change instantly because no signal can propagate faster than the speed of light. In typical circuits the increase in current propagates somewhere between $0.1c$ and $c$.