Powering a light bulb with a battery

Powering a light bulb with a battery
Just connect the positive terminal of the battery with one electrical contact of your light bulb and the negative terminal with the other electrical contact of the bulb. Many bulbs have one electrical contact with screw threads on it, with the other contact as a round dot on the end of the base. Other bulbs will have metal prongs sticking out. It’s notoriously hard to get good electrical contact on batteries and bulbs by soldering wires on. The spring contacts in flashlights work much better (but even they are troublesome from time to time).




It’s important to select a bulb which matches what your battery can put out. If the battery has too low a voltage, the current flowing through the bulb will be small and the bulb’s filament won’t get hot enough to visibly glow. If the battery has too high a voltage, so much current will flow that the filament will get too hot and vaporize.



Standard bulbs are designed to work with a voltage of around 120 V, which is an unusual range for batteries. Ordinary flashlight bulbs are designed to work with about 3V, easy to obtain with two batteries in series. Bulbs from cars are usually designed to work with about 12V, the output of a car battery or of eight standard battery cells in series.



You might think that using a lower voltage would only slightly dim the light, but actually the effect is much more severe. First, the heating power in the bulb goes as the square of the voltage, at least until the voltage gets big enough for the bulb to heat up and increase its resistance. Second, the amount of visible light produced in the bulb is virtually zero until the filament temperature gets close to the standard operating temperature. Thus using one fourth of the power will give much less than one fourth of the light output. If you use a bit too low a voltage, the bulb will glow orangeish, because it can still put out some colors of light but not the blue part of the spectrum.



You yourself generate about 60 W of heating power, the same as a 60 W bulb, but I’ll bet you don’t visibly glow very much. That’s because your temperature is too low to give off visible light. The light you do give off is infrared, which can be detected but not directly by our eyes.

How do I make an electromagnet?

How do I make an electromagnet?

It is fairly easy to build an electromagnet. All you need to do is wrap some insulated copper wire around an iron core. If you attach a battery to the wire, an electric current will begin to flow and the iron core will become magnetized. When the battery is disconnected, the iron core will lose its magnetism. Follow these steps if you would like to build the electromagnet described in our Magnets and Electromagnets experiment:

Step 1 - Gather the Materials

To build the electromagnet described in our Magnets and Electromagnets experiment, you will need:
One iron nail fifteen centimeters (6 in) long
Three meters (10 ft) of 22 gauge insulated, stranded copper wire
One or more D-cell batteries
A pair of wire strippers

Step 2 - Remove some Insulation

Some of the copper wire needs to be exposed so that the battery can make a good electrical connection. Use a pair of wire strippers to remove a few centimeters of insulation from each end of the wire.

Step 3 - Wrap the Wire Around the Nail

Neatly wrap the wire around the nail. The more wire you wrap around the nail, the stronger your electromagnet will be. Make certain that you leave enough of the wire unwound so that you can attach the battery.
When you wrap the wire around the nail, make certain that you wrap the wire all in one direction. You need to do this because the direction of a magnet field depends on the direction of the electric current creating it. The movement of electric charges creates a magnetic field. If you could see the magnetic field around a wire that has electricity flowing through it, it would look like a series of circles around the wire. If an electric current is flowing directly towards you, the magnetic field created by it circles around the wire in a counter-clockwise direction. If the direction of the electric current is reversed, the magnetic field reverses also and circles the wire in a clockwise direction. If you wrap some of the wire around the nail in one direction and some of the wire in the other direction, the magnetic fields from the different sections fight each other and cancel out, reducing the strength of your magnet.
When you wrap the wire around the nail, make certain that you wrap the wire all in one direction. You need to do this because the direction of a magnet field depends on the direction of the electric current creating it. The movement of electric charges creates a magnetic field. If you could see the magnetic field around a wire that has electricity flowing through it, it would look like a series of circles around the wire. If an electric current is flowing directly towards you, the magnetic field created by it circles around the wire in a counter-clockwise direction. If the direction of the electric current is reversed, the magnetic field reverses also and circles the wire in a clockwise direction. If you wrap some of the wire around the nail in one direction and some of the wire in the other direction, the magnetic fields from the different sections fight each other and cancel out, reducing the strength of your magnet.

Step 4 - Connect the Battery


Attach one end of the wire to the positive terminal of the battery and the other end of the wire to the negative terminal of the battery. If all has gone well, your electromagnet is now working!
Don't worry about which end of the wire you attach to the positive terminal of the battery and which one you attach to the negative terminal. Your magnet will work just as well either way. What will change is your magnet's polarity. One end of your magnet will be its north pole and the other end will be its south pole. Reversing the way the battery is connected will reverse the poles of your electromagnet.
Hints to Make Your Electromagnet Stronger


The more turns of wire your magnet has, the better. Keep in mind that the further the wire is from the core, the less effective it will be.
The more current that passes through the wire, the better. Caution! Too much current can be dangerous! As electricity passes through a wire, some energy is lost as heat. The more current that flows through a wire, the more heat is generated. If you double the current passing through a wire, the heat generated will increase 4 times! If you triple the current passing through a wire, the heat generated will increase 9 times! Things can quickly become too hot to handle.
Try experimenting with different cores. A thicker core might make a more powerful magnet. Just make certain that the material you choose can be magnetized. You can test your core with a permanent magnet. If a permanent magnet is not attracted to your core, it will not make a good electromagnet. An aluminum bar, for example, is not a good choice for your magnet's core.