00:02
So here we have a question about a reading lamp that's going to remain turned on for one hour.
00:08
It wants us to find what the cost is to run that lamp for an hour if one kilowatt hour costs $ .075.
00:15
They give us information about the voltage that the lamp is supplied with and the current that runs through it.
00:22
In order to get the answer, we have to find the power that's supplied or the power that the light is giving off.
00:33
In order to help us find out what the cost is.
00:37
So there is an equation allows us to do that.
00:40
That is power is equal to the potential difference or the voltage times current.
00:48
And what we can do is multiply those numbers.
00:52
So we have 120 volts for this delta v and we have current being 2 .6 amps there.
01:05
And when we do that, we end up getting 312 watts of power.
01:13
So that's how much power the lamp uses.
01:19
And if what we can do now is figure out the cost, we will have our answer.
01:24
So what allows us to do that is if we take our power, so the cost is equal to the power times the the number of hours.
01:39
So what we could do is we could put the time in hours over the over 1 ,000, right, 1 ,000.
01:51
And this is the conversion factor that turns the watts from watts to kilowatts.
01:57
So i'm going to show those steps kind of, this is the general formula for it.
02:02
But i'm going to show this in a way where you can kind of see me do the conversion.
02:08
Here so um so what i'm going to do is take our power let's see let's do it over here so we're going to take power of 312 watts and i'm going to convert that to to kilowatts so i know that i know that let's see one kilowatt is equal to 1 ,000 watts so what i can do is take this and i can say well 1 ,000 watts here is equal to one kilowatt there.
02:48
What that does is allow those to cancel, those units to cancel and i'm left with kilowatts.
02:53
So i do 312 kilowatts divided by 1 ,000.
02:59
I get 0 .312.
03:03
So what i can do is kind of update my answer over here...