Multimeter experiment with voltage and current

Description:

Experiment with electricity using a multimeter and a battery.

Equipment Needed:

A multimeter, either a digital multimeter or an analog multimeter.

A battery. A standard AA, C, or D battery will do nicely.

A piece of wire. A straightened paperclip is fine, although any wire long enough to go from one end of the battery to the other will be good.

The Digital Bits Science Lab Experiment:

There are two characteristics of electricity that get measured regularly: the “voltage“, and the “amperage“, or current.

In some ways, electricity is kind of like pumping water. The “voltage” corresponds to how much “pressure” there is forcing the electricity through things, while the “amperage” corresponds to the actual “quantity” of electricity. So, if water were electricity, a big slow-flowing river would have a very low voltage but a very high amperage, while a stream of water jetting out of a power washer would have a very high voltage but a very low amperage. A battery is kind of like a pump for electricity.

So, we will use your multimeter to measure both voltage and amperage of the electricity from a battery, and see how it changes when we “short the battery out”.

First, turn your multimeter selector dial to “DC Volts“, at the lowest range. Touch one probe to each end of the battery. If it is an unused AA, C, or D battery, it should read 1.5 volts. (If you are using an analog multimeter, and the needle tries to turn the wrong direction, just swap the ends of the battery that the probes are touching).

Leaving the probes on the ends of the battery, short it out: take your bit of wire and bend it so the wire touches both ends of the battery. The voltage that you read should drop quite a lot, maybe to almost zero. This is as if we had a power washer, and punched a hole in the hose so that the water could get out more easily, making the pressure drop. If you leave the wire touching both ends of the battery for more than a few seconds, it will start to get hot, so don’t leave it on too long.

Now, turn your multimeter selector knob to “DC mA“. That stands for Direct Current milli-Amperes. Most multimeters only measure up to 250 mA, and when you touch the probes to the battery ends, it will go off the scale (for an analog multimeter), or display some message about being “out of range” (for a digital multimeter). This means that the battery is able to supply a lot more electrical current than your multimeter can measure.

Still leaving the probes on the battery, short it out again with your piece of wire. Now, instead of being out-of-range, the current will drop to something you can read on your scale. Basically, most of the electricity is flowing through the wire, and your multimeter is measuring the current that is “left over”.

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