ShmoopTube

00:04

here's your shmoop du jour brought

00:05

to you by food fries although we've never been food fighters [People throwing food into each others face]

00:09

we've always been food lovers we're going to pour ourselves another glass of [Man sipping gravy]

00:13

gravy and then I get to work an immense food fights broken out in the cafeteria

00:17

in the midst of all the confusion something drops onto Hannah's table

00:20

it's a squishy bag with a countdown timer and it realizes it's a gravy [A bag of TNT appears]

00:25

grenade sure she could run away and save herself

00:27

but Hannah thinks she knows enough about electric circuits to defuse this thing

00:30

less than 10 seconds left anna cuts the wire embraces herself [Hannah cuts wire]

00:35

two-one-zero nothing happens the gravy grenade has been defused she jumps up

00:41

with a booyah and then a mound of mashed potato it's her right between the eyes [Mashed potato strikes hannah in the face]

00:45

take a look at this diagram of the circuit right there yeah all right

00:50

what's the circuit I won in a gravy grenade circuit and your essential

00:55

answers all right well seems like there's an arms race and food fight [Men throw pie into face]

01:00

these days if there are gravy grenades well we're just a few steps away from a

01:04

butter bazooka which could be devastatingly slippery [Man with butter bazooka]

01:06

luckily we can work on disarmament maybe get some kind of cafeteria peace prize

01:10

from the lunch lady well this circuit has two loops which

01:13

means we'll be employing the loop rule the loop rule basically states that when

01:17

following any closed loop around a circuit there is no change in the

01:20

potential there are a few rules that go along with this one when crossing the

01:24

resistor in the same direction as the current the potential drops by current

01:28

times resistance 2 when crossing the resistor in the opposite direction to

01:32

the current the potential increases by current times resistance 3 when moving

01:36

through a battery from negative positive the potential increases by voltage 4

01:41

when moving through a battery from positive to negative the potential

01:45

decreases by voltage well in this circuit we have two loops first we have [loops of circuit highlighted]

01:49

AFEBA let's break this loop down step-by-step keeping in mind the rules

01:54

we just covered from A to F we move through v1 from negative to positive

01:59

which adds positive c1 from F to e we cross our one in the direction of i1

02:05

which adds negative I,1 r1 from E to B we cross our 4 in the direction of

02:12

I 1 plus I 2 which adds negative I 1 plus I 2 times R 4 from B to a there is

02:18

no change the changes in potential along the loop sum to 0 well here's the whole

02:23

thing it's an equation walking out way through the loop CDEBC we'll find an

02:29

equation that looks like this there we go okay we were given the [Equation appears on circuit]

02:33

voltages and resistances so we can plug those numbers into the equations

02:38

well we can simplify those equations and set them as simultaneous now we're

02:42

getting out to break up in here to solve this we multiply the AFEBA loop by 3

02:48

making it easier to deal with the second variable Omega I to remember we're

02:54

solving I sub 1 we then subtract loop C de BC from this equation [Equation appears]

02:59

leaving us with a new equation of a hundred sixty ohms times current I sub 1

03:05

equals 20 volts since current equals volts over resistance we can divide the

03:11

voltage 20 by the resistance 160 to find that current one equals one eight

03:17

amperes meaning the correct answer is a and hopefully everyone has learned their [Man carrying butter bazooka]

03:22

left and when it comes to food fight you know that we're never going to use food

03:25

as ammunition again but then again we're not sure what they feed us in our

03:29

cafeteria actually counts as food [Man turns green after sniffing cafeteria food]

Full Transcript