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Hi guys, This is a pre-lecture for
this Friday's lecture on September 6th, which will be on Kirchoff's laws
in networks.
The way we finished Wednesday's lecture is we talked about
just the basic set up for a telegraph; and, I'd like you to warm up
with this problem,
based on the last lecture. Start by calculating
the number of turns in an electromagnet with the cross-section of
three centimeters squared,
which can live 20 grams across a two millimeter gap 100 km away.
You can assume a 48 V battery,
which is like four car batteries connected in series
(which we'll talk about later),
and the the wire of gauge 12. OK. So, you can pause...
Alright, if you're coming back
let's get going with the new stuff, and
let's discuss: what if we want to broadcast our signal.
Let's say we want to start at Urbana-Champaign, with the switch there
and we want the telegraph to click with the same message
in Bloomington, in Decatur,
and in Springfield. And this is the map of this area.
If you're not familiar with it, it might be useful to take a look.
Alright, so
we can set up like this: we can have the wire running from
Urbana-Champaign, transmitting in the signal to the receiver which is the
electromagnet in Bloomington
then a run into Springfield going to the
electromagnet there and then from Springfield to Decatur gone through
electromagnet there
another receiver and coming back to mention being
that's one possible configuration but we could also do this
from Urbana Champaign we could run a wire well
set of two wires one go in there and one coming back to the Gator
and indicated with branch aw with the
one set of wires going to Bloomington gone through electromagnet there
and coming back and the other I going to
Springfield gone through a commitment there and coming back
right that dramatically it would look something like this:
the better in the switcher and champagne and in the first case
you know the wire just runs continuously here's a symbol for
a bunch of wire which is not coincidentally the same as the symbol
for the resistor
here and we're going through an electromagnet
thats Bloomington run into Springfield gone through electromagnet going to the
Gator
electromagnet and coming back to Champaign
versus the other configuration where we will go to
Decatur here and then one branch will go to Bloomington go through look for a
minute there and come back
and the other branch will go to Springfield go through electromagnet
there
and come back and go through electromagnet indicator
and come back to Champaign I so those are the two configurations
so whether I wanted to do with this right so
for the two configurations figure out all the resistances will start their
good the resistance is for all the wire segments basam
other two geometries in the slider bar and assume
twelve-gauge way right many of these resistances will be the same
so you don't need to do actual too much work to determine which ones are the
same
pretty much I'm and calculate them
I'm we have the formula for their system so
go okay if you're coming back
and would like to do some more
if you're not too tired I'm you can assume that the batteries 48 whoops
and get Lee the currents 3 jours reelect remains were both
other configurations this is working ahead okay this is where we gonna start
the lecture
I'm India can use kar Cubs lost and owns lossy need to read up a little bit and
perhaps lost
are were you some other resources that will give you
I and this is where we will pick up day
thank you right
I think I'll have to be careful to stop the video here