welcome back everybody so in the last um video we did we did this which is um ohm's law v over
i equals r okay and i explained that it was a bit of a puzzle okay puzzles are good fun and
they don't need to be complicated v over i equals r v over i equals r do you remember
so let's just uh redo that oh i think the microphone might be a wee bit close
and this by the way video is suitable if you are studying for the foundation license exam
or anybody else who just might be interested in how to calculate power from uh that's what's
from vaults and amps and resistance and things like that by the way this is on page four of
this book but uh you know if you're interested that's fine i'm not expecting a lot of views on
this video so maybe you would reward me with a thumbs up or if you're a professional you know
all about this you can watch my presentation give me a score out of 10 if you like use the black pen
so to remind us v over i equals r so if we've got 12 volts 2 amps we know that 12 divided by 2 is 6.
good how do we calculate power and by the way i'm going to come on to how to reverse how to reverse
engineer this in the exam because i'll show you the sort of questions they're going to ask
so power watts comes down this line a little bit further what power is and and it's called what's
is again part of this relationship is that v times i is power and we measure power in watts
all right so let's do nice simple example over here we'll do one of the examples we had
last time 12 2 and 6 okay so v over i equals r and i'm going to calculate the power all right so do
red so i'll have 12 volts there we'll have let's say two amps and do you remember how to calculate
the resistance well v over i equals r so 12 divided by two is six so six
similarly we could have calculated um i by doing v divided by r equals i the 12 divided by six is two
easy so what is the how many watts are being consumed if that circuit stayed on all the time
is that we will come down this line here all right this line
so we've got 12 and we've got two how many watts is that 2 12 24
now i could end the video there but i'm gonna show you the sort of question you would get in an exam
okay the sort of question you're gonna get would would miss out some of these
so it might give us 24 watts and it might give us the volts it might even give us the
resistance but it will want to know what the current is and this is going to prove
your understanding of ohm's law and how to work power out so whatever they give you
in the exam it might say something like we've got a circuit that is consuming 24
watts we have a 12 volt circuit consuming 24 watts what is the resistance where that
what what would i do so you get a scrap piece of paper and you do what column says v over i
r and then you put w down there because this line here and we will fill out what what they've asked
so the question is we have a circuit consuming 24 watts so you'll write 24 there
and it will say ah and it's got a 12 volt battery let's say so you'll write 12 there
the question is what is the resistance right well we know that v times i is w
right v times i is w so um or w divided by v is i as well so in power what would the answer be here
because we just need to fill out all the blanks once we've filled out all the blanks we can work
out what the resistance is well that times that is that we know that 212s are 24 okay and 24 divided
by 12 is 2 so we can write 2 in there this is on your scrap piece of paper and then we go right
then what is the resistance this is a standard triangle that callum taught me on the video
uh well v over i equals r so 12 divided by 2 is 6. so the answer is going to be 6. so it will say
we've got 24 watts being consumed at 12 volts what is the resistance you'll be able to work
it out okay i'll do one more for you just in case i was i plundered a bit on there
so we are asked the question in the exam we have a 12 volt battery and we know we are consuming
12 watts of power what is the current okay so you get your scrap piece of paper out and
you'll write it down you know you've got a 12 volt battery because that's going to be
and it said we've got how many what did i just say
i've forgotten i'll start again okay so let's say the question is i have a 12 volt battery consuming
six watts of power six watts of power so you get your scrap paper out and you'll just jot your
six down here and then it will say what is the current and you also got no idea right so what the
only thing we do know is this is ohm's law v over i equals r and we know that's what's
so we need to fill in the blanks all right okay well we know that something times something is
six that'll be a half because half of twelve is six so the answer to this one is going to be 0.5
it might ask what is the resistance okay that's not a problem you've got your little
scrapbook out here 12 divided by 0.5 is r how many halves are there in 12 all right
24. so the answer will be 24. so don't panic just put your own slaw triangle down
draw w down bottom left and gradually fill out all the blanks and that'll be another question asked
hopefully i've done that because this is the second take first take i drove
to the office in the car and thought i could have done that a lot better
i'm not doing it again it's all explained on page four and five and i'm just here to
kind of help you out and give you that extra confidence all right so it's here
page four power and resistance p equals v times i there we are uh it goes on about resistance here
i'm not teaching in the whole blooming book i'm like your brush up lecturer okay next comes
series and parallel circuits light emitting diodes alternating currents and voltages
i'm going to miss all that out your you can read that ac if you don't know about it you have to
look it up i tell you what we'll do next though is frequencies okay how to calculate frequency from
wavelength and all that sort of stuff because that's easy as i said at the beginning if i
deserve it give me a thumbs up and if you've got a different way of explaining this by all means
write me a comment and if you're a lecturer or you do training yourself maybe you can take
something from this you can go oh i wouldn't done it that way but i would have done it that way and
that's good excuse me that's quite interesting all right so from callum here in the bunker and
the next video up here i bid you farewell all the best now i'll see you next time bye for now