Make a Homemade Flashlight!
One of the more memorable school projects I encountered during my
youth was the building of a flashlight from scratch. It taught me a
lot about electricity and showed that what might seem like a
mysterious, unfathomable device was often more simple that it
appeared. That led to the understanding that even complex equipment
could be comprehended if you studied hard enough.
You can acquire the same understanding by making your own flashlight,
with the bonus of having the flashlight to use when you're done. It's
not difficult, and it's not very expensive, either.
The materials are simple and readily available:
Figure 1. The supplies you'll need.
- 1 cardboard tube from a roll of paper towels
- 1 flashlight bulb
- Aluminum Foil (or some pieces of electrical wire)
- Masking Tape
- A flat piece of cardboard
- Two "D" batteries
That's all you need. The flashlight bulb can be obtained almost
anywhere; Radio Shack or an Auto Parts store are sure bets.
Figure 2. Prepare the materials
Cut two circles from the flat piece of cardboard. These will be
used as the ends of the flashlight. Cut a 1/2 slit in the center
of one and carefully poke a hole in the center of
the other. Take two pieces of aluminim foil and fold them 4 or 5
times until you have two long strips about 12 inches by 1/2 inch
each. Cut the cardboard tube to just slightly longer than the
length of the two batteries together. See figure 2.
Figure 3. Putting it all together.
Slip one of the aluminum strips about 3 inches into the cardboard
circle with the slit in it. Fold the short end of the aluminum so
that it makes a small square bump. Insert the light bulb into the
hole in the other cardboard circle. Carefully wrap one end of the
other aluminum strip around the metal side of the bulb's base. Be
sure that the aluminum does not touch the metal tip on the bottom
of the bulb. Insert the two batteries into the cardboard tube.
(Make sure the batteries both point the same way.) Figure 3 shows
Figure 4. Assembling the flashlight.
Fit the two cardboard circles on the end of the tube to hold the
batteries in place. Make sure that the bottom tip of the bulb and
the aluminum square touch the ends of the batteries. Tape the
circles in place with the masking tape. Tape the aluminum strips
along the side of the tube so that they meet and over lap about an
inch or two. Leave the end of one strip free so that it can be
bent back to avoid touching the other strip. See figure 4.
Figure 5. Ready to use!
Turn the flashlight on by pressing the the two aluminum strips
together. If it doesn't light up, make sure that:
To turn it off, simply fold back one of the aluminum strips so
that they no longer touch.
- the bottom aluminum strip is securely touching the bottom
of the batteries,
- the top strip is touching only the side of the bulb,
- the bottom tip of the bulb is firmly touching the top end of
- both batteries are pointing the same way, and
- the two aluminum strips are touching each other without any
tape in between.
Turn out the lights and have fun!
How it works
Electricity flows through metals or other conductive
materials. When you connect the two ends of a battery with a
conductive material, current flows through the
circuit. If there is nothing in the circuit besides the
battery and the conductor, the current flows very freely, resulting
in a drained battery, a very hot conductor, and possibly a fire. This
is often called a short circuit.
To prevent this, a cuircuit should include some sort of load
or resistance to slow the current down. This is usually
accomplished by making the current do some sort of work -- in the case
of a flashlight, that work is lighting the bulb.
In this flashlight, we are using two batteries in series for
a little more oomph. Just as two train locomotives together can pull
a longer train, two batteries can do more work.
To turn the flashlight on and off, we open the circuit by
separating the two strips of aluminum. If there is not a complete path
from one end of the battery to the other, no current will flow.