# Temperature and its Measurement

## Overview

In this chapter, students explore the concept of hotness and coldness, understand what temperature is, and learn how it is measured using different types of thermometers. The chapter also highlights proper techniques for temperature measurement and introduces various temperature scales used in science and daily life.

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## Key Topics Covered

### 1. Hot or Cold?

* Objects can feel hot or cold depending on their temperature.
* Sense of touch is unreliable for measuring temperature due to human perception.
* **Activity**: Hands dipped in hot and cold water may give misleading results when later placed in normal water.
* **Conclusion**: Accurate instruments like thermometers are required.

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### 2. Understanding Temperature

* Temperature is a measure of how hot or cold a body is.
* A hotter body has higher temperature.
* A **thermometer** is used to measure temperature.

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### 3. Types of Thermometers

#### A. Clinical Thermometer

* Measures human body temperature.
* Two types:

* **Mercury thermometers** (now rarely used due to toxicity).
* **Digital thermometers** (more common; battery operated).
* Measures in **Celsius (°C)** and **Fahrenheit (°F)**.
* Normal body temperature: **37°C or 98.6°F**.
* Used under the tongue or in the armpit (slightly lower reading).

#### B. Non-Contact Thermometer

* Also called **Infrared Thermometers**.
* Measures temperature without contact (used during COVID-19).

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### 4. Measurement with a Clinical Thermometer

* Steps:

* Clean thermometer tip.
* Reset it.
* Place under tongue.
* Wait for beep/light.
* Read and record the temperature.
* **Precautions**: Do not immerse digital parts in water. Hold properly. Clean before and after use.

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### 5. Fahrenheit and Kelvin Scales

* **Celsius (°C)**: Common in daily and scientific use.
* **Fahrenheit (°F)**: Earlier used widely in healthcare.
* **Kelvin (K)**: SI unit of temperature, used in scientific work.

* **Conversion**:
`K = °C + 273.15`

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### 6. Laboratory Thermometer

* Used in labs for measuring temperature of liquids and other substances.
* Consists of a **glass tube with bulb** containing mercury or alcohol.
* Range: **–10°C to 110°C**.
* Must be used carefully and correctly.

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### 7. Reading a Laboratory Thermometer

* Each small division usually represents **1°C** (can vary).
* Must be read **while immersed** in the liquid, **vertically**, without touching beaker sides.
* Temperature reading should be **at eye level**.

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### 8. Temperature of Boiling Water and Ice

* Temperature remains **constant** while water boils or ice melts.
* Clinical thermometers cannot measure extreme temperatures like boiling water or ice.

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### 9. Air Temperature

* Measured using **room thermometers** and reported in weather forecasts.
* Changes daily based on season and weather.
* Weather stations record **maximum and minimum** temperatures.

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### 10. Notable Scientist: Anna Mani

* Known as the **Weather Woman of India**.
* Designed weather instruments and worked on renewable energy.

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## New Terms

| Term | Simple Definition |
| ---------------------- | ------------------------------------------------------------------------------- |
| Temperature | How hot or cold something is |
| Thermometer | A tool used to measure temperature |
| Celsius Scale (°C) | A temperature scale where water freezes at 0°C and boils at 100°C |
| Fahrenheit Scale (°F) | A temperature scale commonly used in the USA; 98.6°F is normal body temperature |
| Kelvin Scale (K) | The scientific scale of temperature, starting from absolute zero |
| Clinical Thermometer | Used to measure the temperature of the human body |
| Laboratory Thermometer | Used in labs to measure temperature of substances |
| Infrared Thermometer | A thermometer that measures temperature without touching the object |
| Degree | A unit used to measure temperature in °C or °F |
| Absolute Zero | The lowest possible temperature, 0 K or –273.15°C |

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## 🟢 Easy (3 Questions)

### 1. What is used to measure temperature?

* **A. Thermometer**
* B. Ruler
* C. Compass
* D. Barometer
**Answer**: A
**Explanation**: A thermometer is the instrument used to measure temperature.

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### 2. What is the normal body temperature of a healthy human?

* A. 32°C
* **B. 37°C**
* C. 25°C
* D. 42°C
**Answer**: B
**Explanation**: A healthy human body temperature is approximately 37°C or 98.6°F.

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### 3. Which thermometer can measure temperature without touching?

* A. Laboratory thermometer
* **B. Infrared thermometer**
* C. Mercury thermometer
* D. Digital clinical thermometer
**Answer**: B
**Explanation**: Infrared thermometers are non-contact and measure temperature from a distance.

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## 🟡 Medium (2 Questions)

### 4. Why can't a clinical thermometer measure the temperature of boiling water?

* **A. It has a limited temperature range**
* B. It is too large
* C. It contains mercury
* D. It breaks easily
**Answer**: A
**Explanation**: Clinical thermometers are designed for body temperatures (around 35°C to 42°C), not high temperatures like boiling water (\~100°C).

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### 5. What is the SI unit of temperature?

* A. Degree Celsius
* B. Degree Fahrenheit
* **C. Kelvin**
* D. Joule
**Answer**: C
**Explanation**: Kelvin (K) is the SI unit of temperature used in scientific measurements.

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## 🔴 Difficult (3 Questions)

### 6. Convert 25°C to Kelvin.

* A. 298 K
* B. 250 K
* **C. 298.15 K**
* D. 273.15 K
**Answer**: C
**Explanation**: K = °C + 273.15 = 25 + 273.15 = 298.15 K

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### 7. If a laboratory thermometer has 50 divisions between 0°C and 100°C, what is the value of one division?

* A. 0.5°C
* **B. 2°C**
* C. 1°C
* D. 5°C
**Answer**: B
**Explanation**: 100°C ÷ 50 divisions = 2°C per division.

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### 8. What precautions should be followed while using a laboratory thermometer?

* A. Hold it by the bulb
* B. Read it after removing from liquid
* **C. Keep it vertical and read at eye level while immersed**
* D. Touch the bulb to the beaker bottom
**Answer**: C
**Explanation**: Proper usage requires vertical placement, immersion, and eye-level reading.

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## 🔵 Very Difficult (2 Questions)

### 9. Why does the temperature reading drop when a laboratory thermometer is removed from hot water?

* A. Because the water cools
* **B. Because the thermometer starts cooling immediately**
* C. Due to friction
* D. It’s a defective thermometer
**Answer**: B
**Explanation**: Once removed, the liquid inside cools, lowering the reading.

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### 10. Vaishnavi's temperature record shows 40.0°C at 7 pm on Day One. What does this indicate?

* A. Hypothermia
* B. Normal temperature
* **C. High fever**
* D. Low fever
**Answer**: C
**Explanation**: 40°C is much higher than normal body temperature (37°C), indicating a high fever.

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