Homemade bimetallic strips - Thermostat demonstration // Homemade Science with Bruce Yeany

oh I appreciate it today way to take a

look at bimetallic strips now talk to

your parity simple piece but it has a

lot of applications they control the

temperature inside a water heater or in

your house there's a thermostat which

has a coil bimetallic strip that little

dial on the toaster determines how long

the bread stays down for I think that

was a little bit too long they can make

lights blink on and off and even some

clocks have bimetallic strips to keep

them more accurate now this is a

demonstration bimetallic strip so let's

see how it operates and now I'm going to

show you how you can make your own

version of it and demonstrate it

yourself now this piece is made of two

metals it has brass on one side and iron

on the other side and they've been

pressed together it's not a spring if I

bend it it stays bent but let me

straighten it out here now let's go see

what happens when we heat it

you'll notice as I'm heating the bar

it's starting to curve now why would it

do this brass expands more than the iron

does so when the bar is heated it

expands unevenly with the brass on the

outside and the iron on the inside let's

see what happens when we cool the bar

by adding a little water it's going to

cool the bar back to room temperature

and notice that it's straightening

itself out if we were to freeze this it

would actually Bend in the opposite

direction now it's time to try our own

version of in this case I call it a

biomaterials trip these chips have

aluminum on the outside and heavy stock

paper on the other side but it behaves

the same way if I heat this the aluminum

will expand and curve with the paper on

the inside

now as you can see by heating it we get

a pretty nice curve to it and if we let

this sit eventually that metal is going

to contract and cause this to straight

now so let's take this to the table I'll

speed the camera up here so we see the

results a little bit faster now that

took about two minutes for it to

straighten itself out we could peel it

off and try it again

and of course we're going to get the

same results the aluminum is caught it

caused a strip to expand on evenly just

like the bimetallic strip made of the

brass in the iron let's go see how to

make these our first method is going to

use aluminum tape and a piece of heavy

stock paper I'm simply going to rip off

a piece that's slightly longer than the

paper is pull off the backing and pull

it tight to get any creases out and try

and apply it to the paper as smoothly as


there we go

next I'll use scissors to cut out this

trip to the desired width and length

that I wanted go and there's my buy

material strip another version is to use

mailing labels and simply attach them to

aluminum foil again I'll put them on

here and then I could cut them out

another possibility is to use heavy

stock paper and I can smear some white

glue onto the one side of it go spread

it out nice and smooth so I have a film

covering the whole piece and once again

now I'm going to take this and simply

press it down onto aluminum foil and

that's going to take a while cord to dry

I made a few other ones earlier now I

have to do is simply cut them out now

let's give these a try and see if they

work we'll start with the label that's

attached to aluminum foil heat that up

we can see it bending that's good and

this is the one that was glued here we

go we can see this one bending also

now let's see if we can use these and

apply them to a practical purpose

now at the beginning of this video we

saw these lights out of blinking on and

off there aren't you being controlled by

these by material strips how do they

operate well let's see this experiment

is going to start with a six volt power

source and a six volt light bulb now the

wires from the power source well one's

going to go to this little red post here

and the second one's going to be wired

inside that closed pit you can see it a

little bit closer there now the idea is

if I run a wire from inside the

clothespin over to that post completes a

circuit and the light bulb lights if I

replace that wire with one of the strips

and make contacts on both side the light

bulb lights and if I lift it up and

break the contact it goes out so we're

going to use this to turn the light bulb

on and off now to make it a little bit

more efficient I'm going to carve the

aluminum side with a little bit of black

marker and that's going to help it turn

the radiant energy into thermal energy

and that's going to make it work a

little bit better car it here put it

back in there we go

there are several factors that determine

how quickly this points on and off but I

find once it gets into a rhythm it's

really going to take about 20 or 30

seconds to make that change I've built a

few different versions of this piece so

let's switch over from a 6-volt system

to a 12-volt system this way I'll grab

this one here is now the only real

difference between this piece and the

last one is that this uses a 12 volt

bulb which I got from an auto supply


it's the heat from the light bulb that

causes the biomaterials chip to bend up

slightly great contact and the light

bulb goes off as it cools the strip

comes down and makes contact again and

turns light bulb back on

this is the same basic concept that

bimetallic strips are used to control

the temperature and all sorts of heating