Temperature and its Measurement – CBSE NCERT Study Resources

Temperature measures how hot or cold an object is. Our textbook shows it is measured in degrees Celsius (°C) or Fahrenheit (°F).

A thermometer has a liquid (like mercury) that expands with heat and rises in a narrow tube. The scale helps us read the temperature.

We use thermometers to check fever. For example, doctors place it under the tongue to measure body temperature.

A laboratory thermometer measures temperatures in experiments. It has a higher range than a clinical one.

It has a long stem with a mercury column. We studied that it can measure from -10°C to 110°C.

Unlike clinical thermometers, it cannot measure body temperature. For example, we use it to check water temperature in labs.

Fixed points are standard references to calibrate thermometers. Our textbook mentions ice and steam points.

Ice point is 0°C (melting ice) and steam point is 100°C (boiling water). The scale between them is divided into 100 equal parts.

For example, weather forecasts use these points to describe temperature ranges.

Digital thermometers use sensors to measure temperature and display it digitally.

They have a metal probe that detects heat. Unlike mercury thermometers, they give quick readings without liquid expansion.

For example, we use digital thermometers in kitchens to check food temperature safely.

Shaking resets the mercury level to the lowest reading.

If not shaken, the mercury may stay at a previous reading, giving wrong results. Our textbook shows this as a safety step.

For example, a doctor shakes it to ensure accurate fever measurement.

A thermometer measures temperature using the expansion of liquid. We studied that mercury or alcohol expands when heated.

A laboratory thermometer has a long, narrow tube for precise readings. Unlike a clinical thermometer, it lacks a kink and measures a wider range (-10°C to 110°C). Our textbook shows it is used in labs.

In cooking, we check water temperature, while doctors use clinical thermometers for fever.

Digital thermometers use sensors to detect temperature changes. We studied they give quick readings.

They convert heat into electrical signals displayed on a screen. Unlike mercury thermometers, they are safer and easier to read.

Hospitals use them for accurate fever checks. At home, parents prefer them for kids.

• No risk of mercury poisoning
• Faster results

Water absorbs heat efficiently. We studied it prevents engines from overheating.

In vehicles, water circulates through the engine, absorbing excess heat. A radiator then cools the water using air flow.

Our textbook shows this system in cars. Farmers also use water to cool machinery.

The kelvin scale starts at absolute zero (-273°C). We studied it is used in labs.

Unlike Celsius, kelvin has no negative values. 0 K means no molecular motion. Our textbook shows it for precise experiments.

Scientists use it in space research. Weather reports still prefer Celsius.

A thermos reduces heat transfer. We studied it keeps drinks hot or cold.

It has a vacuum layer to block heat flow. Shiny walls reflect heat. Our textbook shows this design.

Mothers use it for school lunches. Workers carry tea in it.

To measure temperature using a laboratory thermometer, follow these steps:

1. Hold the thermometer vertically to ensure accurate reading.
2. Immerse the bulb completely in the substance whose temperature is to be measured.
3. Wait for the mercury thread to stabilize before taking the reading.
4. Read the temperature at eye level to avoid parallax error.

Precautions:

• Do not hold the thermometer by its bulb as body heat can alter readings.
• Avoid sudden temperature changes to prevent breakage.
• Never use it to measure temperatures beyond its scale.
• Handle with care as mercury is toxic if the thermometer breaks.

Laboratory thermometers are designed for precise measurements in experiments, unlike clinical thermometers meant for body temperature.

Heat and temperature are related but distinct concepts:

Heat is the total energy of molecular motion in a substance, measured in joules (J). For example, a bucket of warm water contains more heat than a cup of boiling water, even though the latter has a higher temperature.

Temperature is the average kinetic energy of molecules, measured in °C, °F, or K. For instance, a spark from a fire has a very high temperature but carries little heat due to its tiny mass.

Key differences:

• Heat depends on mass, temperature doesn't.
• Heat flows from hotter to colder objects, while temperature determines the direction of this flow.
• Thermometers measure temperature, not heat.

Understanding this difference helps explain why large bodies of water moderate climate - they store massive amounts of heat without extreme temperature changes.

To measure temperature using a laboratory thermometer, follow these steps:

1. Hold the thermometer vertically and ensure it is clean.
2. Dip the bulb of the thermometer into the substance whose temperature is to be measured.
3. Wait for the mercury or alcohol thread to stabilize.
4. Read the temperature at eye level to avoid parallax error.

Precautions:

• Do not hold the thermometer by its bulb as body heat can alter readings.
• Avoid touching the sides or bottom of the container while measuring.
• Do not use it for temperatures beyond its range to prevent breakage.
• Handle with care as it contains hazardous materials like mercury.

This method ensures accurate measurement of temperature in liquids or gases.

Clinical Thermometer:

• Structure: Has a kink near the bulb to prevent mercury from falling back.
• Range: Typically measures from 35°C to 42°C, suitable for human body temperature.
• Usage: Used in medical settings to measure body temperature.

• Structure: No kink, allowing continuous measurement.
• Range: Measures from -10°C to 110°C, covering a wider range for experiments.
• Usage: Used in labs to measure temperatures of liquids or gases.

The main difference lies in their design and application, with clinical thermometers being specialized for medical use and laboratory thermometers for scientific experiments.

A clinical thermometer is a specialized device used to measure the human body temperature. It works on the principle of thermal expansion, where the mercury or alcohol inside the thermometer expands when heated and contracts when cooled, indicating the temperature on a calibrated scale.

Differences between clinical and laboratory thermometers:

• Range: Clinical thermometers measure temperatures between 35°C to 42°C, while laboratory thermometers have a wider range (e.g., -10°C to 110°C).
• Kink: Clinical thermometers have a kink near the bulb to prevent mercury from falling back immediately, whereas laboratory thermometers lack this feature.
• Usage: Clinical thermometers are used for medical purposes, while laboratory thermometers are used in experiments.

Procedure to measure body temperature:

The Celsius and Fahrenheit scales are two common units for measuring temperature. The Celsius scale is based on the freezing (0°C) and boiling (100°C) points of water, while the Fahrenheit scale sets these points at 32°F and 212°F, respectively.

Conversion formula: °F = (°C × 9/5) + 32

Significance of 37°C: This is the normal human body temperature. It ensures optimal functioning of enzymes and metabolic processes. A deviation from this value may indicate fever or hypothermia.

Temperature is a measure of how hot or cold an object is, indicating the average kinetic energy of its particles. It is measured in degrees Celsius (°C) or Fahrenheit (°F).

A clinical thermometer is specifically designed to measure human body temperature. Here’s how it is used:

• Shake the thermometer gently to bring the mercury level below 35°C.
• Place the bulb of the thermometer under the tongue or in the armpit for about 1-2 minutes.
• Remove it and read the temperature by observing the mercury level against the scale.

Precautions:

• Do not hold the thermometer by its bulb.
• Wash the thermometer before and after use.
• Avoid touching the mercury bulb with hot or cold objects.
• Never use a clinical thermometer to measure other high-temperature objects.

Clinical thermometers have a kink near the bulb to prevent mercury from falling back, ensuring accurate readings.

Laboratory Thermometer:

• Measures a wide range of temperatures (typically -10°C to 110°C).
• Used in labs for experiments.
• No kink in the capillary tube, so mercury falls back when removed from the heat source.

Clinical Thermometer:

• Measures a narrow range (35°C to 42°C) suitable for the human body.
• Used to measure body temperature.
• Has a kink to prevent mercury from falling back, allowing accurate reading after removal.

A laboratory thermometer cannot measure human body temperature because:

• It lacks a kink, so mercury drops quickly, making it hard to read.
• Its range is too broad, reducing precision for body temperature measurements.
• It is not designed for safe use in the mouth or armpit.

Thus, clinical thermometers are specifically calibrated for human body temperature measurement.

A clinical thermometer is a special type of thermometer used to measure human body temperature. It has a narrow kink near the bulb to prevent the mercury from falling back immediately after removal from the body, ensuring accurate reading.

Working Principle: It works on the principle of thermal expansion. When the thermometer is placed under the tongue or armpit, the heat from the body causes the mercury inside to expand and rise up the capillary tube. The temperature is read from the scale marked on the glass tube.

Differences from a Laboratory Thermometer:

• Range: Clinical thermometers measure between 35°C to 42°C, while laboratory thermometers have a wider range (e.g., -10°C to 110°C).
• Kink: Clinical thermometers have a kink; laboratory thermometers do not.
• Usage: Clinical thermometers are used for medical purposes, while laboratory thermometers are used in experiments.

Diagram: (Draw a labeled diagram showing the bulb, capillary tube, kink, and scale of a clinical thermometer.)

A maximum-minimum thermometer is a special thermometer that records the highest and lowest temperatures over a period of time, usually a day. It consists of a U-shaped glass tube with two separate scales for maximum and minimum temperatures.

Working:
1. The thermometer contains alcohol and a small amount of mercury.
2. When the temperature rises, the alcohol expands, pushing the mercury toward the maximum scale.
3. When the temperature falls, the alcohol contracts, pulling the mercury toward the minimum scale.
4. Two small metal markers (indices) are pushed by the mercury to record the extremes.

Use in Weather Forecasting: It helps meteorologists track temperature variations, which is crucial for predicting weather patterns, planning agriculture, and issuing warnings for extreme conditions.

A clinical thermometer is a special type of thermometer used to measure human body temperature. It has a narrow kink near the bulb that prevents the mercury from falling back immediately after removal from the body, allowing an accurate reading.

Special features of a clinical thermometer:

• It has a temperature range of 35°C to 42°C, suitable for measuring body temperature.
• The kink ensures the mercury stays in place until shaken down.
• It is designed for safe and hygienic use in medical applications.

A laboratory thermometer cannot be used for measuring body temperature because:

• It lacks a kink, so the mercury level drops as soon as it is removed from the heat source.
• Its range is much wider (usually -10°C to 110°C), making it less precise for body temperature readings.
• It is not designed for medical use and may not be hygienic.

To measure the temperature of water using a laboratory thermometer, follow these steps:

1. Immerse the bulb of the thermometer completely in the water without touching the sides or bottom of the container.
2. Wait for the mercury (or alcohol) to stabilize, which usually takes about 1-2 minutes.
3. Read the temperature at eye level to avoid parallax error, noting the meniscus of the liquid inside.
4. Record the temperature in °C (Celsius).

Precautions for accurate readings:

• Do not hold the thermometer by its bulb, as body heat can alter the reading.
• Ensure the thermometer is clean and dry before use.
• Do not use it for temperatures outside its specified range to avoid breakage.
• Avoid sudden temperature changes, as it may crack the glass.

Laboratory thermometers are more precise than regular thermometers and are ideal for scientific experiments where accuracy is crucial.

A clinical thermometer is a special type of thermometer used to measure human body temperature. It works on the principle of thermal expansion, where the liquid inside (usually mercury or alcohol) expands when heated and rises in a narrow glass tube.

Key features of a clinical thermometer:

• Temperature range: 35°C to 42°C (since the human body temperature stays within this range).
• Has a kink near the bulb to prevent the mercury from falling back immediately after removal from the body.
• Used for medical purposes, such as checking fever.

Difference from a laboratory thermometer:

• A laboratory thermometer has a wider range (-10°C to 110°C) and lacks a kink.
• It is used in labs for general temperature measurements, not for body temperature.

Diagram: (Draw a labeled diagram showing the bulb, capillary tube, kink, and scale of a clinical thermometer.)

A maximum-minimum thermometer is a special thermometer that records the highest and lowest temperatures over a period (usually 24 hours). It consists of a U-shaped glass tube with two separate scales for maximum and minimum readings.

Working principle:

• It uses two liquids—alcohol (which expands with heat) and mercury (which pushes small metal markers).
• When temperature rises, alcohol expands, pushing mercury and the maximum marker upward.
• When temperature falls, alcohol contracts, pulling mercury and the minimum marker downward.

Use in weather forecasting: It helps meteorologists track daily temperature variations, which is crucial for predicting weather patterns and extreme conditions.

Diagram: (Draw a U-shaped tube with labeled markers, alcohol, and mercury sections.)