Chapter: 03. Physical Quantities And Measurement 2
CHECK YOUR PROGRESS
Earlier people estimated time by looking at the To record the time interval that has lapsed between two events, we use a SCIENCE TALK
What is the necessity of using the 24-hour clock in some professions instead of following the 12-hour clock? In which professions are they usually followed?
The 24-hour clock is necessary in professions like aviation, military, and emergency services to avoid ambiguity between a.m. and p.m. times. This ensures clarity and precision, which is critical for operations where errors could have serious consequences. LIFE SKILLS
Jatin is travelling to his grandparent’s house by train. The journey is 5 hours 12 minutes long. The train leaves at 1500 hours and stops midway for 15 minutes. His grandmother asks him at what time he will reach. To answer her question, Jatin converts the arrival time in a 12-hour clock format. What will Jatin’s answer be?
Jatin’s answer will be 8:27 p.m. Implied Questions from Text
A child is having chills and is shivering. His friend suggests him to measure his body temperature.
Which thermometer should he use? He should use a clinical thermometer or a digital thermometer. Where should he place the thermometer? He should place the thermometer below the tongue or under the armpit. How long should he keep the thermometer in position to get the correct reading? He should keep the thermometer for about two minutes (for a clinical thermometer) or until the digital thermometer beeps. PREPPING FOR PISA
Assertion (A): Two bodies with the same temperature always possess the same amount of heat energy.
Reason ®: The factors which affect the heat possessed by a body also affect its temperature. d. Both A and R are false. Two cubic blocks P and Q have different sizes but are made up of the same material. P and Q contain heat energy of 30 J and 80 J, respectively. What will happen if they are brought in contact with each other? c. There will be no transfer of heat energy. (Based on the passage, heat transfer depends on temperature difference, not just the amount of heat energy. Without knowing their temperatures, we cannot determine heat flow direction.) EVACOATION
A. Choose the correct option.
The standard unit of time in SI system is Which of the following instruments measure time most accurately? A clinical thermometer is marked from The normal body temperature of a person is Why is it advised not to hold a thermometer by its bulb while reading it? HOTS d. Both a and c. (Mercury in the bulb expands, and it gives a false reading.) B. Write true (T) or false (F) against the following statements.
1. A clinical thermometer measures the temperature of boiling water.
* F
2. Nowadays pendulum clocks are used since they are very accurate.
* F
3. The standard unit of temperature in SI system is degree Celsius.
* F
4. Stopwatches are used to record the time interval that has lapsed between two events.
* T
C. Fill in the blanks.
1. A slight bend or kink in a clinical thermometer is called a constriction.
2. Time taken by the Earth to complete one rotation about its own axis is called mean solar day.
3. The Samrat yantras in the Jantar Mantars at Jaipur and Delhi are examples of sundials.
4. In a thermometer, mercury appears as a shiny thread.
D. Name the following:
14. the physical quantity that measures how hot or cold an object is * Temperature
15. a liquid commonly used in laboratory thermometers * Mercury
16. the thermometer used to measure the temperature of a human body * Clinical thermometer
17. the interval between two events * Time
E. Short answer type questions.
What is the standard unit of time in SI system? How is it related to a mean solar day? * The standard unit of time in the SI system is the second (s). A mean solar day is 24 hours, which is equal to 86400 seconds.
What is temperature? State its standard unit in SI system. * Temperature is the degree of hotness or coldness of a body. Its standard unit in the SI system is kelvin (K).
How do we come to know that a person is suffering from fever? * We come to know that a person is suffering from fever if their body temperature, measured with a clinical or digital thermometer, is above the normal body temperature of 37° C or 98.6° F.
F. Long answer type questions.
What are the differences between a laboratory thermometer and a clinical thermometer? * A laboratory thermometer is used to measure room temperature or the temperature of solids and liquids in a lab, typically having a range from -10° C to 110° C and no constriction. A clinical thermometer is used to measure human body temperature, has a narrower range (typically 35° C to 42° C), and includes a constriction (kink) to prevent the mercury level from falling immediately.
Explain the purpose of a constriction in a clinical thermometer. * The purpose of a constriction (slight bend or kink) in a clinical thermometer is to prevent the mercury level from dropping back into the bulb immediately after the thermometer is removed from the patient’s mouth. This allows enough time for the user to read the patient’s temperature accurately before the mercury falls.
Higher Order Thinking Skills (HOTS)
Tick the option(s) which correctly identify why a laboratory thermometer cannot be used to measure human body temperature. c. It does not have a kink. (Also, implicitly, its range is not precise for body temperature and mercury falls quickly) Can we use a clinical thermometer to measure the temperature of boiling water? Explain. No, a clinical thermometer cannot be used to measure the temperature of boiling water. This is because its measuring range is typically only up to 42° C, while boiling water is 100° C. The high temperature would cause the mercury to expand beyond the thermometer’s scale, potentially breaking it. Additionally, the constriction would hinder the measurement of such a high temperature. Numericals
How many seconds are there in 8 hours and 30 seconds? 8 hours = 8 × 60 minutes × 60 seconds/minute = 28800 seconds. Total seconds = 28800 seconds + 30 seconds = 28830 seconds. How many hours are there in 14 days? 14 days = 14 × 24 hours/day = 336 hours. Convert the following 12-hour time into 24-hour time.
a. 9:20 pm
* 2120 hours
b. 10: 40 am
* 1040 hours Learning by Doing
In which year did the French create a standard unit of measurement? The French created a standard unit of measurement in 1799. What is this standard unit of measurement called? This standard unit of measurement is called the metre. Measure your pulse in one minute at rest. Now hop 20 times and measure your pulse again. Answer the following questions.
a. What is your pulse rate at rest?
* (This is a personal answer, but an example could be: My pulse rate at rest is approximately 70 beats per minute.)
b. Is your pulse rate higher after hopping? Find out why.
* Yes, my pulse rate is higher after hopping. This is because physical activity like hopping requires more energy, which means the heart needs to pump more oxygenated blood to the muscles. To meet this increased demand, the heart beats faster, leading to a higher pulse rate. 
Answers to textbook exercises