Basic Circuits Kit: Pencil Resistors


[whoosh] [ding] Hi, this is Ben Finio with
Science Buddies and this video will show you how to use your Basic Circuits Kit for the
pencil resistors project. So here we have all the parts in the kit, you have four double
A batteries, you have a three double A battery holder so your kit comes with one extra battery,
you have a small light bulb, a light bulb base, and three alligator clips which get
their name because they have these little metal jaws that can grab on to wires and circuit
components. To assemble your kit first you’re going to put three batteries in the battery
holder. Look closely at the batteries, you see that there are plus signs on one end of
the batteries, there are also plus signs printed inside the battery holder. Make sure those
plus signs line up. You can also check the flat end of the battery is the side that goes
up against the spring. So put three batteries in the battery holder and then put the fourth
battery aside. Next just screw the light bulb into the base, and now you are ready to connect
everything with the alligator clips. So we’re going to color code here, take the red alligator
clip and connect it to the red wire from the battery pack, take the black alligator clip
and connect it to the black wire, oops you can see so these alligator clips will hold
on kind of snugly but if you pull too hard they will come off, so I lost the red one
there I’m going to reattach that. Now here’s one important safety note, at this point you
want to make sure that the red and black alligator clips do not touch each other directly. That
will create a short circuit and can cause your battery pack to get very hot. So keep
those nice and spaced out, away from each other on your table so they don’t bump into
each other. Now you’re going to take your light bulb holder, and it has these two little
screws on it on either side that you can connect the alligator clips to. Now it will be a little
easier to connect to those if you actually take a small Philips head screwdriver and
loosen the screws slightly. That kind of gets the surface up away from the bottom so it’s
not flush there and it will be easier to get them with the alligator clips. So once you’ve
loosened those a little bit, take the other end of the black alligator clip, connect it
to one of the screws, and now take the green alligator clip which you haven’t used yet
and connect it to the other screw. So as of right now, we still have an open circuit.
There is no complete path for the electricity to flow so this light bulb does not light
up. However if I take the free ends of the red and green alligator clips and touch them
together, I have a closed circuit so electricity can flow in a loop through this red wire,
through the green alligator clip, through the light bulb and then back through the black
alligator clip and wire to the battery pack. So check that your light bulb lights up when
you touch these two alligator clips together. If it does not light up, make sure that all
your connections are secure and you don’t have a loose alligator clip and you did not
put a battery in the battery pack backwards, and once that’s working you are ready to
start your experiment. For the pencil resistor project you will make resistors out of pencils
by cutting them to various lengths and then sharpening them on both ends. To connect them
to your circuit, use the alligator clips and clip on to the graphite tip on both ends.
Make sure you do not connect to the wood and that the metal from the alligator clip actually
makes contact with the graphite. You can see that when I do that, the light bulb lights
up much dimmer than it did before when I connected the two alligator clips directly to each other.
But again, be careful, you’ll see that if I clip on and don’t make good contact with
the graphite and I’m only touching the wood, the light bulb will not light up at all and
that will affect the results of your experiment. So make sure the metal from the alligator
clip makes good contact with the graphite tip of the pencil. To conduct your experiment
you will make multiple pencils of different lengths and measure how the length of the
pencil affects the brightness of the light bulb. For directions for thousands of other
science and engineering projects you can do for school or at home, visit us online at
www.sciencebuddies.org.