Temperature and Its Measurement Class 6 Notes | CBSE Science

Hoshi noticed something strange: a steel spoon and a wooden spoon were sitting in the same room, but the steel one felt much hotter to touch. Same room. Same surroundings. Why? The answer lies in understanding temperature — what it is, how we measure it, and why it matters. This is your complete CBSE guide to this chapter.

What Is Temperature?

CBSE Definition — write this in your exam

Temperature is the measure of the degree of hotness or coldness of an object or substance.

When you touch a cup of hot tea, your hand feels warm. When you hold an ice cube, your hand feels cold. This difference in feeling is because the tea and the ice have different temperatures. A higher temperature means an object is hotter; a lower temperature means it is cooler.

Temperature is measured using an instrument called a thermometer.

💡 Remember: Temperature and heat are not the same thing. Temperature is a measurement. Heat is a form of energy. We cover this important difference below.

What Is a Thermometer?

A thermometer is an instrument used to measure temperature. Most thermometers contain mercury — a silvery liquid metal that expands when heated and contracts when cooled. As mercury moves up or down a thin glass tube, we can read the temperature from the scale marked on the tube.

There are two types of thermometers you need to know for Class 6 CBSE:

  • Clinical thermometer — used to measure human body temperature
  • Laboratory thermometer — used to measure temperature in science experiments

Clinical Thermometer

A clinical thermometer is the thermometer a doctor or nurse uses to check if you have a fever. It is designed specifically for measuring the temperature of the human body.

Key features:

  • Range: 35°C to 42°C (or 94°F to 108°F) — covers the full range of human body temperatures including high fever
  • Has a kink: a small bend just above the bulb. This prevents mercury from falling back when removed from the mouth, so the reading stays visible
  • Must be jerked before use: shake the thermometer downward a few times before each reading to bring mercury below 35°C
  • Placed under the tongue or armpit to take a reading
✅ Exam-ready answer

Q: What is the use of a kink in a clinical thermometer?

A: The kink in a clinical thermometer prevents mercury from flowing back into the bulb after the thermometer is removed from the patient's mouth. This allows the temperature reading to remain visible even after removal.

How to use a clinical thermometer:

  1. Wash the thermometer with cold water and wipe clean with antiseptic.
  2. Jerk it downward to bring mercury below 35°C.
  3. Place it under the tongue (or in the armpit) and keep the mouth closed.
  4. Wait for 1–2 minutes, then remove it.
  5. Read the temperature at eye level, holding it horizontally.

Laboratory Thermometer

A laboratory thermometer is used to measure temperature in science experiments — for example, to measure the temperature of water being heated, or a cooling liquid in a beaker.

Key features:

  • Range: −10°C to 110°C — a much wider range than a clinical thermometer
  • No kink: mercury falls back as soon as it is removed from the substance, so you must read it while it is still submerged
  • Never used for body temperature: it is not designed for this purpose
  • Must be held upright while reading
  • The bulb must be fully submerged in the substance being measured
⚠️ Common mistake

Never use a laboratory thermometer to measure human body temperature. Its range goes up to 110°C — far too high for body use, and its design makes an accurate body-temperature reading impossible. Always use a clinical thermometer for the human body.

Clinical vs Laboratory Thermometer — Comparison Table

This table is one of the most frequently asked topics in Class 6 Science exams. Know it well.

Feature Clinical Thermometer Laboratory Thermometer
Used for Measuring human body temperature Measuring temperature in experiments
Range 35°C to 42°C −10°C to 110°C
Kink Yes — prevents mercury falling back No kink
Reading Can be read after removing from mouth Must be read while still in the substance
Jerking before use Yes, required before every use Not needed

Temperature Scales: Celsius and Fahrenheit

Temperature is measured using two scales. You need to know both for CBSE Class 6.

Celsius (°C)

The Celsius scale is used in India and in science. Key values:

  • Water freezes at 0°C
  • Normal human body temperature: 37°C
  • Water boils at 100°C

Fahrenheit (°F)

The Fahrenheit scale appears on clinical thermometers alongside Celsius. Key values:

  • Water freezes at 32°F
  • Normal human body temperature: 98.6°F
  • Water boils at 212°F

Heat vs Temperature — The Key Difference

This is one of the most common points of confusion — and one of the most common exam questions.

Heat Temperature
A form of energy A measurement
Flows from hot to cold objects Tells us how hot or cold an object is
Measured in Joules (J) or Calories Measured in °C or °F
A large pot of lukewarm water contains more heat than a small cup of boiling water The boiling water has a higher temperature

Safety Rules When Using a Thermometer

These appear as short-answer questions in CBSE exams. Know at least three:

  • Never hold a thermometer by the bulb — always hold by the upper end
  • Never wash a thermometer with hot water — it may break or give a wrong reading
  • Do not tilt a laboratory thermometer while reading — keep it upright
  • Read the thermometer at eye level to avoid parallax error
  • Keep the bulb of a laboratory thermometer fully submerged while measuring
  • Do not use a laboratory thermometer to measure body temperature