Lets assume that each student at LCC uses his or her cell phone for a total of 2.5 hours of straight usage each day. Lets also assume that each cell phone battery lasts for 270 minutes of usage, and each students cell phone charger draws .2 amperes and 5.1 volts from the wall for two hours to fully charge the cell phone.
Refer to the following for unit definitions:
J= Joules s= seconds A= amperes V= voltage W= Watts
First we find the power that the charger draws from the wall:
Power = Current x Voltage
P=I x V
P= (.2 A) (5.1 V)
P= 1.02 W used each second while charging one single cell phone
1.02 W= 1.02 J/s
Next we find the amount of time assumed it takes to charge one cell phone per day.
The average assumed time to charge a cell phone is 2 hours
2 hrs x (3600 s/ 1 hr) = 7200 s to charge a single cell phone
Then we take the time it takes to charge a cell phone per day and multiply it by the power it takes to charge the cell phone.
1.02 J/s x (7200 s) = 7344 J used to charge one cell phone per day
Since we assume that a person needs to charge their cell phone every other day throughout the entire year, we do the following:
365 days per year/2 = 182.5 days a year in which a person would need to charge his or her cell phone
Next we take the amount of days a person charges his or her cell phone a year and multiply it by the energy it takes to charge a cell phone once.
(7344 J) x (182.5 days) = 1,340,280 J/year used by one person
Finally in order to find the amount used by LCC students as a whole (assuming LCC has 2,600 students using cell phones) we must multiply the following numbers:
(1,340,280 J/year) x (2,600 students) = 3,484,728,000 J/year by LCC students