simple experiments for kids
if their dads will let them simple
experiments for dads and wonderful
experiments when you've lost your car in
a car park and can't find it
i want to talk about my key fob and
central locking device on it and you
press this button and the lights flash
and the
point is that this sends out
electromagnetic waves now the
the frequency of these waves depends on
whether you get a car in north america
or elsewhere for one it's about 320
megahertz i can't remember the exact
details the other is about 400 and 300
megahertz means that
the wavelength of these electromagnetic
waves is about a meter it's about so big
now then the whole point is that this
has a range if i walk away from the car
the signal coming out gets weaker and
weaker and weaker and there's a clever
trick which i found on youtube with
jeremy clarkson in top gear explaining
that if you have one of these key things
the central locking device the range can
be extended if you place the key against
your head i really wanted to know
whether this is true but i couldn't
believe it so what i want to do today is
to explain how it works but first i must
show you that it works
one two three four five six that's 20
paces if i use this you see even with my
arm extended i can get the lights to
turn on
i'll now go another 15 paces this way
and show you
uh that the car won't lights won't go on
unless i put this against my head so
here we go one two three four fifteen
and now if i
press the key
nothing happens
but if i press the key placing it next
to my head something happened now the
reason this works is because
everybody's brain
everybody's head is full of water so i
got over there some water which i'll go
and collect and we'll go another 20
paces that way and show you that the
water will extend the range even further
so just don't go away for a minute i'll
just go get it you think this is going
to be entertaining enough
one two three four five
even when i get here
the lights will flash ah i must get away
from the water
we're just about at the limit of the
range
of using your brain it doesn't work now
then
ah i can't hold it let's put it way up
there
i'm pressing now
there we go
when the electromagnetic waves goes into
the water
all the water molecules see more or less
the same electric field sloshing through
it
the electric field
moves the positive charges that is the
protons or the hydrogen ions one way and
the oxygen ions the other so
in effect what you've got is two protons
being pushed upwards and then pulled
downwards and pulled upward and
downwards
because of this oscillating electric
field
that means that they're behaving rather
like a radio aerial the electrons are
going up and down up and down radiating
energy now if i point my key that way
there is a ray going straight from me to
the car
but it's also going into the bottle of
water over here on my head over here and
the water in my head is going up and
down in synchronization with the rays
coming out of this because you're so
close together if you're a half a
wavelength you'll be completely out of
phase but because you're close you're in
phase and these waves add together the
wave coming from my
key the waves coming from the water in
my head often the water in a bucket and
that's the reason why these two add
together and extend the range
of my car keys there aren't obvious
parallels with this in physics in the
everyday world this seems to be one of
the few that i everybody can play around
with because they have these lovely keys
central locking devices for their cars
so you can do experiments at home i
didn't believe it and the only way of
finding out whether something is true is
to do the
the damned experiment
do the damned experiment find out what
is reality disprove your prejudices
okay