KS3 · Physics

Measuring temperature

You know a cup of tea is hotter than an ice cream. But “hotter” isn't a measurement. How do you turn “how hot” into a number everyone agrees on?

Physics · Temperature

Build the Celsius scale

This line runs from 0 °C to 100 °C. Drag each tag to where you think it sits, then check.

Ice — Pure ice meltingFridge — Inside a fridgeRoom — Room temperatureBody — Human core body temperatureBoil — Pure water boiling

Inside a thermometer

The laboratory glass thermometer

View: Warmed. Showing 3 layers: Glass tube and bulb, Liquid — bulb warmed, Scale

View

Explore

switch Warmed / Cooled, then tap a part

Warm the bulb and the coloured liquid rises up the tube.

A thermometer is any device that measures temperature. There are several kinds: a gun thermometer you point at something without touching it, a digital medical thermometer, and this one, the glass thermometer used in the lab. Switch between Warmed and Cooled, then tap each part.

Physics · Temperature

Put a scale on a blank thermometer

You have a glass thermometer with no numbers on it. Mark a Celsius scale on it, then work out where the 40 °C line goes.

Put the bulb in pure melting ice. When the liquid settles, mark its level: that's 0 °C.
missing step

Which line is step 2?

Put the bulb in pure boiling water. When the liquid settles, mark its level: that's 100 °C.Put the bulb in water at room temperature. When the liquid settles, mark its level: that's 100 °C.Put the bulb in pure boiling water. Mark the level straight away, before the liquid settles: that's 100 °C.

Physics · Measuring safely

Find the slip in Sam's method

Sam measured the temperature of boiling water with a glass thermometer and a Bunsen burner. One line of this method is unsafe. Which one?

Sam's method — which line goes wrong?

I put on eye protection.
I took the thermometer out of its tray and held it between the soft pads of a clamp on a stand.
I lit the Bunsen burner, then put the beaker of water in place and lowered the thermometer into it.
I made sure the bulb of the thermometer was fully inside the water.
When the water was boiling, I waited for the coloured liquid to settle.
Keeping my face away from the steam, I read the scale with my eye level with the top of the coloured liquid.
I didn't touch any of the apparatus until the hot parts had cooled down.

Physics · Temperature

The door and the handle

A wooden door and its metal handle have been in the same room all night. The room is at about 20 °C.

Which is closest to what you think right now?

The metal handle is at a lower temperature than the door, because metal is a cold material.The handle feels colder when I touch it, so it must be at a lower temperature.Each one is still at whatever temperature it was when it was first put there.They are both at the same temperature: room temperature, about 20 °C.

How sure are you?

I'm sureI think soI'm guessing

The metal handle is at a lower temperature than the door, because metal is a cold material.

This is a common misconception

It's a really common idea, but temperature doesn't depend on what something is made of. Left in the room long enough, the wood and the metal both end up at room temperature, about 20 °C.

The handle feels colder when I touch it, so it must be at a lower temperature.

This is a common misconception

Your hand isn't a thermometer. A thermometer is the device that measures temperature, and it would give the same reading for the handle and the door: room temperature, about 20 °C. How something feels is not a measurement.

Each one is still at whatever temperature it was when it was first put there.

This is a common misconception

Objects don't hang on to their starting temperature. Left for long enough, everything in a room ends up at the same temperature: room temperature.

They are both at the same temperature: room temperature, about 20 °C.

This matches the evidence

Exactly right. Left for long enough, all the objects in a room reach the same temperature, whatever they are made of. The handle and the door are both at about 20 °C.

Leave anything in a room for long enough and it reaches room temperature, whatever it's made of. Wood, metal, plastic: same room, same temperature.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Two fixed points, a hundred equal steps, one unit — °C

What you need to know

What temperature measures, and how to write its unit: °C
The parts of a glass thermometer and what the coloured liquid does when the bulb is warmed or cooled
How a scale is put on a blank thermometer using two fixed points
How to take a temperature reading accurately and safely
Some everyday temperatures, and why objects in the same room end up at the same temperature

The big picture

Temperature is a measure of how hot or cold something is, in degrees Celsius (°C). A glass thermometer shows it with coloured liquid that rises when the bulb is warmed and drops when it is cooled. Its scale is made from two fixed points, melting ice at 0 °C and boiling water at 100 °C, with the gap split into 100 equal steps. Measure with the bulb fully in, the liquid settled and your eye level with the top of it. Left long enough, everything in a room reaches room temperature.

Key points

1Temperature is a measure of how hot or cold something is. A cup of tea has a higher temperature than an ice cream.

2Temperature is measured in degrees Celsius, written °C, with a capital C because the unit is named after a person, Celsius.

3A thermometer measures temperature. Types include the gun thermometer, the digital medical thermometer and the glass laboratory thermometer.

4In a glass thermometer, warming the bulb makes the coloured liquid rise up the tube; cooling it makes the liquid drop. The reading comes from the scale.

5Pure ice melts at 0 °C and pure water boils at 100 °C. These fixed points are marked, then the distance between them is divided by 100 to find the length for 1 °C.

6For an accurate reading: bulb fully in, wait for the liquid to settle, eye level with the top of the liquid.

7Everyday temperatures: a fridge is about 5 °C, a room usually about 20 °C, human core body temperature about 37 °C.

8Left long enough, all objects in a room reach the same temperature, room temperature, whatever they are made of.

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Worked example

Problem

Priya puts a scale on a blank thermometer. Her 0 °C and 100 °C marks are 20 cm apart. She puts the bulb in some warm water, and when the liquid settles its top is 5 cm above the 0 °C mark. What temperature is the water?

⚠ Watch out

Writing the unit wrongly: “25 c”, “25 C°” or just “25 degrees”. Write the number, then °C: a small raised circle, then a capital C, because the unit is named after Celsius.

🧠

Memory hook

Ice 0, fridge 5, room 20, you 37, boiling 100. Two fixed ends, a hundred equal steps.

✓

Check yourself

Without scrolling up: why does making a thermometer's scale need two fixed points and not just one? What goes at each end, and what do you do with the gap in between?

Flashcards

(13)

What does temperature measure?

How hot or cold something is. A cup of tea has a higher temperature than an ice cream.

What unit is temperature measured in, and how is it written?

Degrees Celsius, written °C: a small raised circle, then a capital C (the unit is named after a person, Celsius).

What is a thermometer?

A device that measures temperature.

Name three types of thermometer.

A gun thermometer (pointed at an object without touching it), a digital medical thermometer, and the glass thermometer used in the lab.

What are the main parts of a glass thermometer?

A glass tube with a bulb at the bottom full of coloured liquid, and a scale marked on the tube.

What happens to the coloured liquid when the bulb is warmed? And cooled?

Warmed: it rises up the tube. Cooled: it drops.

What are the two fixed points of the Celsius scale?

Pure ice melts at 0 °C; pure water boils at 100 °C.

The 0 °C and 100 °C marks on a thermometer are a known distance apart. How do you find the length for 1 °C?

Divide the distance between the marks by 100.

Three things to do for an accurate thermometer reading?

Put the bulb fully inside what you're measuring, wait for the liquid to settle, and read with your eye level with the top of the liquid.

Where should a glass thermometer be kept, and how is it held while measuring?

Stored in a tray; held between the soft pads of a clamp on a stand.

Measuring boiling water: what gets done before the Bunsen burner is lit?

The apparatus is set up, with the thermometer in the water.

Roughly how hot is a fridge, a room and the inside of the human body?

Fridge about 5 °C, room usually about 20 °C, human core body temperature about 37 °C.

A metal handle and a wooden door have been in a room all night. Which is at the higher temperature?

Neither. Both are at room temperature. Left long enough, everything in a room reaches the same temperature, whatever it's made of.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Build the Celsius scale

Put a scale on a blank thermometer

Find the slip in Sam's method

The door and the handle

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