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### Course: AP®︎/College Physics 1>Unit 11

Lesson 7: DC Circuit analysis

# Current due to closing a switch: worked example

Find the current due to closing a switch using equivalent resistance and Ohm's law.

## Want to join the conversation?

• Is there a difference between the instant a switch is closed and a few minutes after a switch is closed for the current if say there was no break in the wire giving the current another path and placing the switch elsewhere?
(1 vote)
• There's no resistance through the switch when it is closed?
(1 vote)
• Yes, correct. When a switch is closed, it is treated as a wire.
(1 vote)
• Why would the current follow the path of least resistance? Wouldn't it get divided?
(1 vote)
• Well, here is how I like to think about it, the electrons would want to travel through a wire with the least resistance the exact same way any of us would want to take the easiest route back home. We wouldn't want to do the extra work would we? and the same way the electrons too would not want to do the extra work.

For example: Imagine you have a simple circuit, with a single wire connecting a resistor and a battery while forming a closed loop. Now, if you connect a second wire (that has way less resistance as compared to the first) to the circuit, let's say from a random point A on the first wire before the resistor to a random point B on the first wire after the resistor. This offers the electrons the choice to not pass through the resistor they had initially travelled through (this is actually called a short circuit). The electrons (most of them, we can't just suspend ohms law) then would take the wire with lesser resistance, ie the second wire .
(1 vote)
• If I remove the R1 in both case then if I close the switch then I create a short circuit and fry everything?