# Video: Identifying a Measuring Instrument for Measuring the Thickness of a Wire

Which of the following items can be used to measure the width of a wire? [A] A protractor [B] A thermometer [C] A balance [D] A meter ruler [E] A micrometer

03:27

### Video Transcript

Which of the following items can be used to measure the width of a wire, A) protractor, B) a thermometer, C) a balance, D) a meter ruler, E) a micrometer?

Okay so in this case, we’re trying to measure the width of a wire. So let’s go through the options one by one and see what each item actually does, starting with a protractor. Now a protractor is an object, usually semicircular, that we can use to measure the angle between for example two lines. Let’s say this is the first line and this is the second. Well the protractor can be used by aligning one of the lines with the zero mark on the protractor and then reading off the angle value at the next line. So protractors are for measuring angles not distances. Therefore, option A is not the answer we’re looking for.

Option B then, a thermometer, a thermometer is actually used to measure temperature. So if we wanted work out, albeit with great difficulty, how hot our wire was, then we would use a thermometer. However, a thermometer is not useful for measuring the width of a wire. So option B is not the one we’re looking for either. Option C then, a balance, now balances come in various forms. For example, we can have a digital mass balance which we can place objects onto and the mass balance would tell us the mass of these objects, or we can have this old- fashioned seesaw-like contraption, where on one side you place a mass of known value and on the other you place your object. Now in this case, the mass balance seesaws back and forth. So one side can move up and the other side can move down or vice versa. But when the masses of the two objects are absolutely equal, then the level of the two parts of the seesaws are exactly the same. But in either of these cases, a mass balance is used to measure the mass of an object, not the width of a wire. So option C isn’t our answer either.

Option D then a meter ruler, now a meter ruler is more like it because it’s a device used to measure distances. And in theory, we could use a meter ruler to measure the width of a very thick wire. However, when we say wire, we’re generally talking about long thin pieces of metal. And their thinness means that their width, which is this distance that we’re trying to measure, is generally about the same or less than the smallest graduations on a meter ruler, because generally the smallest graduations on a meter ruler are every millimeter. So if we wanna measure the width of our wire with any level of precision, then a meter ruler is not going to do because we can only measure to the nearest millimeter. Plus, using a long meter ruler is a bit of a faff away trying to measure the width of a wire. And so we can cross out option D as well.

This means that option E must be our answer: a micrometer. Now a micrometer is an interestingly shaped device which can be used to measure pretty small distances. Now the way that it works is that we put our wire into the gap between this end of the micrometer and this end. By the way, in this diagram, the way that we’ve drawn wire, it’s going into the screen. So we’re looking at a cross section of the wire. Now with this micrometer, what we can do is to turn this knob right at the end clockwise. And what this does is actually screw in this end of the micrometer such that it moves closer towards the end of the wire. Once the wire is held tightly between the two ends of the micrometer, we know that we’ll get an accurate reading for the width of the wire. And the reading itself is found somewhere on this part of the micrometer. And it measures to a much higher precision than a meter ruler. Sometimes the precision can be even as good a thousandth of a millimeter, or in another words a micrometer, hence the name of the device: a micrometer. And so our final answer is that a micrometer can be used to measure the width of a wire.