How much energy, in joules and in kW•h, is consumed by a 120 W light bulb if it is left on for 15 min?

With steps please

2 Answers
Feb 21, 2018

I got #0.03 \ "kWh"=1.08*10^5 \ "J"#.

Explanation:

We first need to do some conversions here.

Know that:

#1 \ "kW"=1000 \ "W"#

#1 \ "hour" = 60 \ "minutes"#

#:.120 \ "W"=0.12 \ "kW"#

#:.15 \ "minutes" = 0.25 \ "hours"#

So, the bulb uses

#0.12 \ "kW" * 0.25 \ "h"=0.03 \ "kWh"# if it's left running for #15# minutes.

But, we need to convert to #"kWh"# into joules #("J")#. Know that,

#1 \ "kWh"=3.6*10^6 \ "J"#

#:.0.03 \ "kWh"=0.03*3.6*10^6 \ "J"=1.08*10^5 \ "J"#

Feb 21, 2018

Converting given values in desired units, #WtokW# and #minto hr#

Energy consumed #=120/1000xx15/60=0.03\ kWh#

We know that #1\ kWh=3.6xx10^6\ J# or (#1\ Js^-1=1\ W#)

#:.# Energy consumed #=0.03xx3.6xx10^6=1.08xx10^5\ J#