# Video: Identifying a Measuring Instrument for Measuring Temperature

Which of the following instruments is used to measure temperature? [A] A light gate [B] An ohmmeter [C] A thermometer [D] A weighing scale [E] A measuring cylinder

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### Video Transcript

Which of the following instruments is used to measure temperature? A) A light gate, B) An ohmmeter, C) A thermometer, D) A weighing scale, E) A measuring cylinder.

Okay, so here we’re trying to measure temperature. Let’s look at each one of the options one by one. So first of all, a light gate. A light gate is commonly a U-shaped device which has usually an infrared light going from one tip of the U shape to the other. Now a light gate is used to accurately measure the point in time, at which the beam of light gets broken, for example, by an object passing through the light gate.

Therefore, a light gate is most often used to measure some sort of time, whether that’s the time at which this object is passing through the light gate or the time interval between the object passing between two light gates. Either way, light gates are not used to measure temperature.

So let’s look at option B, an ohmmeter. Now an ohmmeter is a device used in an electric circuit to measure electrical resistance. Of course, the unit of resistance is ohms. Therefore, this device is called an ohmmeter. And so this is not the answer to our question either.

Option C then, a thermometer. Now a thermometer is indeed used to measure temperature. The way this works is that if the thermometer is placed in a warmer region, then the level of liquid in the thermometer rises. But that’s particular to this type of thermometer.

There are many different kinds of thermometers including digital thermometers as well nowadays. But they’re all used to measure temperature. The clue is in the name because it’s a thermometer. In other words, it measures some sort of thermal quantity or temperature. And so option C looks like the correct answer.

But let’s look at option D and E very quickly as well. Option D then, a weighing scale. Now a weighing scale can come in many different forms such as this digital weighing scale here. But they’re always used to measure the mass of an object or of course the weight of the object depending on how we calibrate it. Either way, they’re not used to measure temperature.

And finally, option E, a measuring cylinder. Now a measuring cylinder is basically a hollow cylinder that we can fill up with liquid, so as to measure the volume of that liquid. And so it doesn’t measure temperature.

Hence, we have our final answer. The instrument used to measure temperature is a thermometer.