If a metal wire carries a current of 0.10 A, how long does it take for 5.00x1018 electrons to pass a given cross-
sectional area of the wire? (The charge on one electron is 1.6x10-19 C.)

8 seconds

Explanation:

The current in a wire is defined as

where

q is the charge passing through a given point of the wire in a time t

In a metal wire, the current is generally carried by electrons. So, the charge passing through a certain point of the wire can be written as

where

N is the number of electrons

is the fundamental charge (the charge of one electron)

So the formula becomes

In this metal wire we have

I = 0.10 A is the current in the wire

is the number of electrons

Solving for the time, we find:

measuring things 1 litre of water