# Net current in a solenoid or torroid

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1. Oct 8, 2014

### paulina

The notion of multiplying the current in each loop in a toroid or solenoid with the total number of loops in order to find out the net current in the toroid or solenoid is appearing a bit confusing.
Why do we do this when we know the same current is flowing through each loop (just like water flowing in a pipe)?
When the wire is a straight conducting wire we take the net current as ' i ' but in toroid or solenoid it is
' n.i ' where n is the number of turns of the coil. What is the cause for this?

2. Oct 8, 2014

### Staff: Mentor

Current is the amount of charge that flows across a defined surface in a unit time. Generally, you take the surface to be the cross section of the wire, but you can choose a different surfsce. Sometimes, the surface of interest is one crossed by n wires each carrying a current of I. The charge crossing such a surface in a unit time is nI, so the current through that surface is n times the current through the wire.

3. Oct 8, 2014

### paulina

thanks for the explanation...