Multimeter experiments and introduction

Description:

“Your Multimeter and You”: use a multimeter to measure electrical resistance of things, including yourself.

What is a multimeter? Multimeters are instruments to measure several different things, including electrical conductivity, electrical current, and electrical voltage. You can get very cheap ones (see the photo below). You’ll find them at hardware stores for approximately $10 - $20, or you can spend tens, hundreds, or even thousands of dollars for really high-end professional models.  I recommend one of the cheap ones. These can either have a needle and dial reading like the one shown here (analog multimeters) or a numerical display (digital multimeters).

Equipment Needed:

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

You

A metal object, like a coin

A piece of plastic, wood, or glass

A pencil with the eraser pulled off of one end so that you can see the pencil lead

The Digital Bits Science Lab Experiment:

A multimeter has many different settings, the one we are going to use is one of the ones marked “R” (for resistance) or “Ohms”:

This setting is used to measure how easily electricity flows through an object. What the multimeter does is this: it has a battery inside that is connected to the probes.  When you touch the probes to an object, electricity flows from the battery through the object.  If a lot of electricity flows, that means the object has very little electrical resistance, while if hardly any electricity flows, that means the object has very high electrical resistance. The multimeter measures the electrical current flow, and uses this to calculate the resistance of the object in units called “Ohms”.

So, turn the settings selector on your multimeter to measure resistance. First, check the calibration of your multimeter.  With the probes not touching each other, the reading should be “infinite resistance”, meaning no electricity is flowing. When you touch the probes together, the multimeter should read zero resistance, meaning that the current is flowing through the probes as quickly and easily as possible.

Now, we are ready to make some measurements. 

First, check a metal object: the resistance should be very close to zero ohms because metals are very good conductors of electricity.

Next, plastic or wood: the resistance should be extremely high, because these are all very bad conductors of electricity (insulators).

Now try the pencil: touch the multimeter probes to the lead on each end of the pencil.  You should get a reading of somewhere around 10 to 100 ohms. This means that the pencil lead (graphite) will conduct electricity, but that it is not as good of a conductor as most metals.

Finally, try yourself: grab hold of one probe in each hand, and see what your resistance is (don’t worry, the battery in the multimeter is not strong enough to give you a shock).  If your hands are dry, you will probably have nearly infinite resistance.  If your hands are sweaty, or if you lick your fingertips before taking hold of the probe, you should have
a resistance somewhere around 50,000 ohms.  If you touch the probes to your tongue, the resistance should be much lower.

So, this means that while your body has a lot of resistance, it has less resistance than an insulator like a piece of wood.  This is why you can get electrically shocked (because electricity can flow through your body), and why electrical appliances near water are a bad thing (because if you are wet, you have a lot less electrical resistance than if you are
dry).

Other articles related to this topic:

• Multimeter experiment with voltage and current
• Multimeter experiments with electricity and water
• Pick up thousands of rice grains with a pencil
• How to electroplate copper
• Easy electrolysis - how to make your own hydrogen