Chapter 7: Temperature and Its Measurement

Touch can trick; thermometers tell. Learn to measure temperature accurately using the right instruments the right way.

"Wrong measurements are worse than no measurements at all."
— Anna Mani

Big Ideas (Why this chapter matters)

  • Touch can trick; thermometers tell. You can feel hot or cold, but only a thermometer gives a reliable number.
  • Temperature is the measure of hotness/coldness; we use scales (°C, °F, K).
  • Use the right thermometer the right way:
    Clinical (digital) → body temperature.
    Laboratory → liquids/air in experiments.
  • Read correctly (no parallax, correct position), else the number is wrong—even with a good instrument.

Hot or Cold? (Activity idea)

Three-bowl demo:

Right hand in warm water (A), left in ice-cold (C) for 1–2 min → then both into tap water (B).

  • • One hand feels B cool, the other warm—the same water!

Memory hook:

Takeaway: "Touch can trick, thermometers tell."

Clinical Thermometer (Digital) — for body temperature

Digital, battery-run, easy-to-read. Safer than mercury (mercury is toxic).

How to use (D.A.R.T.)

  1. DDisinfect/clean the tip; keep display dry.
  2. AApply under tongue (mouth closed) or in armpit for children/elderly.
  3. RRead when it beeps/flashes.
  4. TTidy up: clean & dry the tip after use.

"Normal" human temperature:

About 37.0 °C (98.6 °F), but varies slightly with age, time of day, and activity.

Important notes:

  • • Armpit readings are typically 0.5–1.0 °C lower than core body temperature.
  • • Non-contact infrared thermometers measure from a distance.

Laboratory Thermometer — for liquids/air (not for the body)

Parts:

  • • Long glass stem
  • • Bulb with liquid (often coloured alcohol or mercury)
  • • Celsius scale on stem

Read it correctly (V.I.E.W. rule)

V

Vertical

Hold the thermometer upright.

I

Immersed

Bulb fully in the liquid; don't touch beaker sides/bottom.

E

Eye-level

Eyes in line with the top of the liquid column (avoid parallax).

W

While-in

Read while immersed; as soon as you take it out, the column falls.

Do not use a lab thermometer to measure body temperature (range/design unsuitable; reading drops on removal).

Mini-Labs (class-ready)

  1. 1
    Touch vs Thermometer: Do the three-bowl activity; reflect why touch misleads.
  2. 2
    Body Temp Log: Record your temperature morning/noon/evening for a week; notice patterns.
  3. 3
    Find Least Count: Inspect your lab thermometer; calculate the smallest division value.

HOTS / Exam-Style Practice

  1. 1

    Why is touch unreliable for detecting fever? Use the three-bowl reasoning.

  2. 2

    List four precautions for using a lab thermometer and explain why for each.

  3. 3

    A thermometer has 50 divisions between 0 °C and 100 °C. What is its least count?

Quick Recap

  • Temperature measures hotness/coldness; thermometers give reliable numbers.
  • Clinical (digital): body only; Lab: liquids/air (–10 to 110 °C typical).
  • Read with V.I.E.W. (Vertical, Immersed, Eye-level, While-in).

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