Suppose your phone charges from 0% to 100% in I4 hours, where I is the electric current (amps/hour) supplied by your charger. Imagine you can make the current as weak or strong as you want.
(a)
What are the possible values for I?
Solution:
The charging time is given by
I4 hours
A zero or negative current would never charge the phone (zero current gives infinite time; negative would drain its battery). Therefore,