TEMPERATURE AND ITS MEASUREMENT – Class 6 : Science
SUMMARY
What is Temperature?
Temperature tells us how hot or cold an object is.
It shows the degree of hotness.
Instruments for Measuring Temperature
Thermometer is used to measure temperature.
Laboratory thermometer: used in experiments.
Clinical thermometer: used by doctors to measure human body temperature.
Units of Temperature
Common units are Celsius (°C), Fahrenheit (°F), and Kelvin (K).
In daily life, Celsius is most commonly used.
Human Body Temperature
Normal body temperature = 37°C or 98.6°F.
How to Read a Thermometer
Keep the thermometer upright.
Place the bulb of thermometer in contact with the substance.
Wait for the mercury level to settle, then note the reading.
Precautions while Using a Clinical Thermometer
Do not use it for very hot things.
Hold it carefully, as it is made of glass.
Always wash before and after use.
Never keep it in direct sunlight.
Heat vs Temperature
Heat is the energy transferred between objects.
Temperature measures the degree of hotness of a body.
SHORT QUESTION AND ANSWERS
Q: What is temperature?
A: Temperature is the measure of how hot or cold an object is.
Q: Which instrument is used to measure temperature?
A: Thermometer.
Q: What is the unit of temperature in the metric system?
A: Degree Celsius (°C).
Q: What is the SI unit of temperature?
A: Kelvin (K).
Q: What is the normal temperature of the human body in Celsius?
A: 37°C.
Q: What is the normal temperature of the human body in Fahrenheit?
A: 98.6°F.
Q: Which thermometer is used to measure human body temperature?
A: Clinical thermometer.
Q: Which thermometer is used in laboratories?
A: Laboratory thermometer.
Q: What is present inside a clinical thermometer?
A: Mercury.
Q: What is the range of a clinical thermometer?
A: 35°C to 42°C.
Q: What is the range of a laboratory thermometer?
A: –10°C to 110°C.
Q: What is the freezing point of water in Celsius?
A: 0°C.
Q: What is the boiling point of water in Celsius?
A: 100°C.
Q: What is the freezing point of water in Fahrenheit?
A: 32°F.
Q: What is the boiling point of water in Fahrenheit?
A: 212°F.
Q: What should be done before using a clinical thermometer?
A: Shake it to bring mercury below 35°C.
Q: Why should a thermometer not be kept in direct sunlight?
A: Because it can break or give wrong readings.
Q: Why is mercury used in thermometers?
A: Because it expands uniformly and is visible.
Q: Which type of thermometer is used in hospitals nowadays instead of mercury thermometers?
A: Digital thermometer.
Q: What does a digital thermometer display?
A: Temperature reading directly in numbers.
Q: What is the difference between heat and temperature?
A: Heat is energy, temperature is the degree of hotness.
Q: Who discovered the Fahrenheit scale?
A: Gabriel Fahrenheit.
Q: Who discovered the Celsius scale?
A: Anders Celsius.
Q: What is the Kelvin value for 0°C?
A: 273 K.
Q: What is the Kelvin value for 100°C?
A: 373 K.
Q: What is the lowest possible temperature in nature?
A: 0 K (absolute zero).
Q: Can a laboratory thermometer measure body temperature?
A: No.
Q: Why can’t a laboratory thermometer be used to measure body temperature?
A: Because it does not have a constriction to hold mercury.
Q: What precaution should be taken while using a laboratory thermometer?
A: The bulb should be fully immersed in the substance.
Q: What should be avoided while handling a thermometer?
A: Sudden jerks and dropping.
Q: What is the body temperature of a healthy person?
A: 37°C or 98.6°F.
Q: Why is mercury preferred over colored alcohol in thermometers?
A: Mercury does not stick to glass and gives accurate readings.
Q: What happens to mercury when temperature increases?
A: It expands and rises in the tube.
Q: What happens to mercury when temperature decreases?
A: It contracts and falls in the tube.
Q: Can digital thermometers be used safely for children?
A: Yes.
Q: Why should mercury thermometers be handled carefully?
A: Because mercury is poisonous.
Q: What should be done after using a clinical thermometer?
A: Wash it with clean water.
Q: Which scale is mostly used in India for weather reports?
A: Celsius scale.
Q: Which scale is mostly used in the USA for weather reports?
A: Fahrenheit scale.
Q: What is the device used to measure very high temperatures in furnaces?
A: Pyrometer.
LONG QUESTION AND ANSWER
Q1. Explain the difference between heat and temperature with suitable examples.
Ans. Heat is the energy that flows from a hotter body to a colder body, while temperature is the measure of the degree of hotness of a body. For example, a cup of tea and a bucket of water may have the same temperature, but the bucket contains more heat as it has more water.
Q2. Describe the structure of a clinical thermometer and explain how it works.
Ans. A clinical thermometer is a narrow glass tube with a bulb at one end containing mercury. It has a constriction near the bulb that prevents mercury from falling back quickly. The thermometer has a scale marked from 35°C to 42°C. When placed under the tongue or in the armpit, mercury expands and rises, indicating body temperature.
Q3. Write a note on laboratory thermometer. How is it different from a clinical thermometer?
Ans. A laboratory thermometer is used to measure temperatures in science experiments. It has a mercury bulb and a long glass tube with a scale usually ranging from -10°C to 110°C. Unlike a clinical thermometer, it has no constriction, so mercury moves up and down freely. A laboratory thermometer cannot be used to measure body temperature.
Q4. Why are precautions necessary while using a clinical thermometer? List them.
Ans. Precautions are necessary because a clinical thermometer is made of glass and mercury, both of which can be dangerous if broken. The precautions are:
Wash before and after use.
Do not place in very hot substances.
Read at eye level.
Do not shake hard to avoid breakage.
Always store safely in its case.
Q5. Explain the different temperature scales used in measurement.
Ans. There are three main temperature scales:
Celsius scale – Freezing point of water = 0°C, boiling point = 100°C.
Fahrenheit scale – Freezing point = 32°F, boiling point = 212°F.
Kelvin scale – Absolute zero = 0 K, freezing point = 273 K, boiling point = 373 K.
In daily life Celsius is commonly used, Fahrenheit in medicine, and Kelvin in science.
Q6. How do you correctly use a laboratory thermometer to measure the temperature of a liquid?
Ans. To measure liquid temperature:
Hold thermometer vertically.
Dip bulb in liquid without touching container walls.
Wait for mercury to stop rising.
Take reading at eye level.
This ensures accurate measurement of the liquid’s temperature.
Q7. What is the importance of temperature measurement in daily life? Give examples.
Ans. Temperature measurement is important in many ways:
Doctors use it to check fever.
In cooking, correct temperature ensures proper food preparation.
In industries, controlling temperature helps in production of chemicals, medicines, and metals.
Weather reports use temperature to predict climate conditions.
Scientists use it in experiments.
Q8. Explain why clinical thermometer cannot be used in laboratories.
Ans. Clinical thermometer has a limited range of 35°C to 42°C, which is only suitable for measuring human body temperature. In laboratories, temperatures may go much higher or lower, so clinical thermometers are not suitable. Also, the constriction in clinical thermometers prevents mercury from moving freely, making them unfit for laboratory use.
Q9. Discuss the role of thermometers in healthcare and medicine.
Ans. In healthcare, thermometers are essential tools:
Clinical thermometers help detect fever in patients.
Digital thermometers give quick readings.
Infrared thermometers are used to measure body temperature without contact, useful in hospitals.
Thermometers also help monitor temperature in incubators, operation theatres, and storage of medicines and vaccines.
Q10. Why is mercury used in thermometers? Are there alternatives to mercury thermometers?
Ans. Mercury is used because it is shiny, visible, expands uniformly with heat, and does not stick to glass. It remains liquid over a wide temperature range. However, mercury is poisonous, so safer alternatives like alcohol thermometers and digital thermometers are now widely used.
Q11. Describe the working of a digital thermometer. Why is it considered safer?
Ans. A digital thermometer works with electronic sensors that detect temperature changes and display the value on a digital screen. It does not use mercury, making it safe and easy to use. It provides fast readings and can store memory. It is widely used in hospitals and homes.
Q12. Why is it advised not to use a laboratory thermometer to measure body temperature?
Ans. Laboratory thermometers have a range of -10°C to 110°C and no constriction. If used for body temperature, mercury level will fall as soon as it is removed, making it impossible to record. Also, the long tube may hurt the patient. Hence, only clinical thermometers are suitable for the human body.
Q13. Explain the precautions to be taken while using a laboratory thermometer.
Ans. Precautions are:
Do not tilt the thermometer, keep it vertical.
The bulb should not touch container walls.
Read at eye level.
Handle carefully to avoid breakage.
Do not dip in very hot substances suddenly.
Q14. How is body temperature measured? What is the normal human body temperature?
Ans. Body temperature is measured using a clinical thermometer. It is placed under the tongue or in the armpit for about a minute. The normal human body temperature is about 37°C (98.6°F). Any rise above this indicates fever.
Q15. What is absolute zero? Why is it important in science?
Ans. Absolute zero is the lowest possible temperature, equal to 0 Kelvin (-273°C). At this temperature, all molecular motion stops. It is important in science because it represents the theoretical limit of coldness and is used in physics experiments.
Q16. Compare Celsius and Fahrenheit scales with examples.
Ans. The Celsius scale sets freezing point of water at 0°C and boiling point at 100°C. The Fahrenheit scale sets freezing point at 32°F and boiling at 212°F. For example, 37°C body temperature equals 98.6°F. Celsius is used in most countries, while Fahrenheit is used in the USA and medical practice.
Q17. How does a thermometer measure temperature? Explain the principle.
Ans. A thermometer works on the principle that substances expand on heating and contract on cooling. In thermometers, mercury or alcohol expands and rises in the glass tube when heated. The scale on the tube allows reading of the temperature.
Q18. Explain why alcohol is sometimes used instead of mercury in thermometers.
Ans. Alcohol is used because:
It expands more than mercury, so small changes are visible.
It remains liquid at very low temperatures (-100°C), suitable for cold regions.
It is safer than mercury as it is not poisonous.
Thus, alcohol thermometers are used for low-temperature measurements.
Q19. How is fever detected and why is it important to measure body temperature during illness?
Ans. Fever is detected by measuring body temperature with a clinical thermometer. If the temperature is higher than 37°C, it indicates fever. Measuring temperature helps doctors diagnose infections, monitor recovery, and decide treatment.
Q20. What is the use of thermometers in weather forecasting?
Ans. Meteorological departments use maximum-minimum thermometers to record daily temperatures. This helps predict heat waves, cold waves, rainfall, and climate conditions. Farmers, travelers, and industries depend on weather temperature data.
Q21. Differentiate between digital and mercury thermometers.
Ans.Mercury thermometers use mercury expansion; digital thermometers use electronic sensors.
Mercury ones are fragile and poisonous; digital ones are safer.
Digital thermometers give faster and more accurate readings.
Mercury thermometers need careful handling.
Q22. What are the advantages and disadvantages of using mercury thermometers?
Ans.Advantages: Accurate readings, wide temperature range, long life.
Disadvantages: Mercury is poisonous, glass breaks easily, unsafe for children, not environment-friendly.
Q23. Explain the use of maximum and minimum thermometer.
Ans. A maximum-minimum thermometer is used in weather stations. It records the highest and lowest temperatures in a day. This helps in studying climate, agriculture, and environment.
Q24. Why should thermometers be read at eye level?
Ans. Thermometers should be read at eye level to avoid parallax error, which occurs when reading from an angle. Eye-level reading ensures accuracy.
Q25. What are the safety concerns with mercury thermometers?
Ans. Mercury is toxic if inhaled or touched. A broken thermometer can release harmful vapors. It can pollute water and soil. Hence, digital thermometers are preferred today.
Q26. Explain how heat transfer affects temperature measurement.
Ans. Heat always flows from hot to cold objects. If a thermometer is placed in a hot liquid, heat flows into mercury, making it expand. If placed in ice, heat flows out of mercury, making it contract. This principle helps measure temperature.
Q27. Why should we not dip a hot thermometer suddenly in cold water?
Ans. The sudden change in temperature can crack the glass due to rapid contraction. Also, mercury might separate into droplets. Hence, thermometers must be cooled gradually.
Q28. Describe the invention and development of thermometers.
Ans. Galileo is believed to have invented the first thermometer in the 16th century. Later, Fahrenheit invented the mercury thermometer in 1714. Celsius introduced the 0–100°C scale. Kelvin developed the absolute scale used in science. Over time, digital and infrared thermometers were invented for safer and faster readings.
Q29. How does temperature affect our daily life activities?
Ans. Temperature affects health, cooking, storage of food, agriculture, industry, weather forecasting, and scientific experiments. It influences lifestyle, clothing, and living conditions.
Q30. Write a short note on modern thermometers used today.
Ans. Modern thermometers include digital, infrared, ear, and non-contact thermometers. They are faster, safer, and more accurate. They do not use mercury, making them eco-friendly. They are widely used in homes, hospitals, airports, and industries.
MCQS
Which instrument is used to measure temperature?
a) Barometer
b) Thermometer
c) Hygrometer
d) Compass
Answer: b) Thermometer
The unit of temperature commonly used in daily life is:
a) Kelvin
b) Fahrenheit
c) Celsius
d) Joule
Answer: c) Celsius
Normal human body temperature is:
a) 35°C
b) 37°C
c) 39°C
d) 40°C
Answer: b) 37°C
Clinical thermometers measure temperature in:
a) Celsius only
b) Fahrenheit only
c) Both Celsius and Fahrenheit
d) Kelvin
Answer: b) Fahrenheit only
What is the boiling point of water on Celsius scale?
a) 0°C
b) 50°C
c) 100°C
d) 212°C
Answer: c) 100°C
Which thermometer is used in laboratories for experiments?
a) Clinical thermometer
b) Laboratory thermometer
c) Digital thermometer
d) Alcohol thermometer
Answer: b) Laboratory thermometer
98.6°F is equal to:
a) 35°C
b) 36°C
c) 37°C
d) 38°C
Answer: c) 37°C
In a clinical thermometer, the constriction in the capillary tube prevents:
a) Mercury from falling back
b) Glass from breaking
c) Scale from shifting
d) Heat transfer
Answer: a) Mercury from falling back
Which of the following is a unit of temperature?
a) Newton
b) Watt
c) Kelvin
d) Pascal
Answer: c) Kelvin
What should not be done while using a clinical thermometer?
a) Wash before use
b) Shake down mercury level
c) Keep in boiling water
d) Place under tongue
Answer: c) Keep in boiling water
The freezing point of water is:
a) 0°C
b) 100°C
c) 212°F
d) 37°C
Answer: a) 0°C
Which gas thermometer is used for accurate scientific purposes?
a) Mercury gas thermometer
b) Constant volume gas thermometer
c) Digital thermometer
d) Clinical thermometer
Answer: b) Constant volume gas thermometer
Which is the SI unit of temperature?
a) °C
b) °F
c) Kelvin (K)
d) Joule
Answer: c) Kelvin (K)
What liquid is usually used in thermometers?
a) Water
b) Mercury
c) Oil
d) Alcohol only
Answer: b) Mercury
0 Kelvin equals to:
a) -273°C
b) 0°C
c) 100°C
d) 273°C
Answer: a) -273°C
Which thermometer does not use mercury?
a) Clinical thermometer
b) Laboratory thermometer
c) Digital thermometer
d) Constant volume thermometer
Answer: c) Digital thermometer
Fever in human body is indicated when temperature rises above:
a) 35°C
b) 37°C
c) 39°C
d) 40°C
Answer: b) 37°C
Which scale is used in most scientific work?
a) Fahrenheit
b) Celsius
c) Kelvin
d) Rankine
Answer: c) Kelvin
A thermometer works on the principle of:
a) Expansion of mercury or alcohol on heating
b) Contraction of glass
c) Heat conduction
d) Electricity
Answer: a) Expansion of mercury or alcohol on heating
The maximum and minimum thermometer is used for measuring:
a) Body temperature
b) Weather temperature
c) Room temperature only
d) Boiling point
Answer: b) Weather temperature
