Temperature Notes with Examples & Videos
Introduction to Temperature
Temperature is a measure of how hot or cold an object or substance is.
We describe temperatures as cold, warm, or hot, but for accurate comparisons we use a thermometer and a temperature scale.
Everyday Examples
- Water from a refrigerator feels cold.
- Boiling water feels very hot.
- In cold weather, people wear thick clothes to stay warm.
- Ceramic floors feel colder than wooden floors.
- Boiling water is hotter than boiling paraffin.
Measurement of Temperature
Temperature is measured using a tool called a thermometer.
Different types include clinical thermometers, digital thermometers, and infrared thermometers.
Fixed Points of a Thermometer
| Fixed Point | Celsius (°C) | Kelvin (K) |
|---|---|---|
| Melting point of pure water | 0°C | 273K |
| Boiling point of pure water | 100°C | 373K |
Temperature Scales
Celsius Scale (°C)
On the Celsius scale, the melting point of water is 0°C and the boiling point is 100°C.
Kelvin Scale (K)
Kelvin is the SI unit for temperature. It starts at absolute zero and does not use a degree symbol (K instead of °K).
Conversion Between Celsius and Kelvin
Formulae
Celsius to Kelvin:
K = C + 273
Kelvin to Celsius:
C = K − 273
Example 3.35
Convert 70°C to Kelvin.
Solution:
K = 70 + 273
K = 343K
Example 3.36
Convert 305K to Celsius.
Solution:
C = 305 − 273
C = 32°C
Change in Temperature
To find the change in temperature, subtract the initial temperature from the final temperature:
Temperature Change = Final − Initial
Example 3.37
Water at 80°C cools to 33°C. Find the temperature change.
Solution:
Change = 80 − 33
Change = 47°C
Exercise 3.6
1. Convert to Kelvin
67°C =
K = C + 273 → 67 + 273 = 340K
95°C =
95 + 273 = 368K
12°C =
12 + 273 = 285K
45°C =
45 + 273 = 318K
2. Convert to Celsius
298K =
C = K − 273 → 298 − 273 = 25°C
350K =
350 − 273 = 77°C
312K =
312 − 273 = 39°C
450K =
450 − 273 = 177°C
3. Change in Temperature
Water at 298K is heated to 350K. What is the change?
Change = 350 − 298 = 52K
4. New Temperature in Kelvin
A metal at 20°C gains 300°C. What is its new temperature in Kelvins?
20 + 300 = 320°C
320 + 273 = 593K