O Level Notes : Physics - Temperature

Welcome back everyone! How are you? Today we’re going to study in detail about temperature, and this is in fact a really easy topic. Okay, so many people mix temperature and heat, very wrong it is. Heat refers to the amount of thermal energy that is transferred from a hotter to a colder region. Temperature is something different.

Definition:

So, what is the difference then? Temperature is the degree of hotness or coldness of a room, a bowl of soup or that of ice cream.

Temperature is measured using the instrument thermometer with which we all are familiar.

Task: Google how a thermometer is made.

Thermometer:

I won’t go in much detail about the making of thermometer, just briefly: an appropriate substance is chosen e.g. mercury because it varies continuously with changes in temperature, then two fixed points are chosen called the upper and the lower fixed point and lastly a scale is calibrated within the two fixed points. Also, you should all know how the two fixed points are marked, it is by placing the thermometer bulb in melting ice and on steam respectively for the lower and upper fixed points.

Now, suppose you have a thermometer with the upper and lower fixed points marked on it but it is not calibrated, and you also know where a certain point is whose temperature you have to find. You know the lengths of all three points. And the question is to find the temperature of the unknown temperature. All you have to do in such a question is insert the values of the known lengths. Here:

Ѳ°C = (l_Ѳ - l₀) / (l₁₀₀ - l₀) x 100

where Ѳ°C is the unknown temperature, l_Ѳ is the length of the unknown temperature, l₁₀₀ is the length of the 100°C (the upper fixed point) and l₀ is the length of the lower fixed point i.e. 0°C.

Try solving this question using the formula to see if you actually got it.

Q1. In an unmarked mercury thermometer, it was found that the length l₀ was 5 cm and the length l₁₀₀ was 25cm. What is the temperature when l_Ѳ is (a) 14 cm, (b) 3 cm?

Thermocouple Thermometer:

Okay so a thermocouple is shown above, it basically consists of two wires made of different metals such as iron and copper as shown above. The ends of wires are joined together to form junctions. The unknown temperature labelled above is then calculated using the reading on the voltmeter (mV in the diagram).

How does this happen? Hmm..well, the two different temperatures causes a small voltage to be produced, greater the difference, greater is the voltage.

Task: Google the advantages of using thermocouple thermometer.

Answers:

Q1. (a) 45°C

(b) -10°C