Answer key

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Last edited 26 days ago by Learn LoopHQ.

Chapter: 03. Physical Quantities And Measurement 2

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Answer Key - Long Answers

Heat and temperature are interconnected but distinct concepts. Temperature is defined as the degree of hotness or coldness of a body, representing the average kinetic energy of its particles. Heat, on the other hand, is a form of energy that is transferred due to the motion of constituent particles and is responsible for the sensation of hotness or coldness. Heat transfer between two bodies can only occur if there is a difference in their temperatures, always flowing from the higher temperature to the lower temperature body. Crucially, two bodies can have the same temperature but different amounts of heat if their sizes or number of constituent particles differ, illustrating that temperature is an intensive property while heat is an extensive one.

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The 12-hour clock divides the 24-hour day into two periods: a.m. (ante meridiem, before midday) and p.m. (post meridiem, after midday), requiring these specifiers to indicate whether the time is morning or evening (e.g., 6:20 a.m. or 6:20 p.m.). In contrast, the 24-hour clock uses a continuous scale from 0000 to 2400 hours without a.m. or p.m. (e.g., 0620 hours for 6:20 a.m. and 1820 hours for 6:20 p.m.). The 24-hour system is highly unambiguous, making it essential and commonly used in professions where precision and clarity are critical, such as aviation, military, and emergency services.

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Historically, people first estimated time by observing natural phenomena like the positions of the sun and moon. This led to early inventions such as sundials, which measured time by casting shadows, exemplified by the Samrat Yantras. Other early mechanical methods included water clocks, candle clocks, and sand clocks (hourglasses). Over time, more sophisticated instruments like spring-driven clocks and pendulum clocks were developed, offering greater accuracy. Today, we primarily use highly precise electronic or digital watches and clocks for daily timekeeping. For highly specific measurements, stopwatches are used for intervals, and atomic clocks, based on atomic vibrations, represent the pinnacle of precise time measurement.

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The constriction in a clinical thermometer is a slight bend or kink located in the capillary tube just above the mercury bulb. Its primary purpose is to prevent the mercury level from rapidly dropping back into the bulb once the thermometer is removed from the patient’s body. This design feature is crucial because it allows the user enough time to accurately read the patient’s temperature without the mercury level falling due to ambient temperature changes. To reuse the thermometer, the mercury must be forced back down below the constriction by giving the thermometer a few firm jerks.

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A laboratory thermometer is designed to measure a wide range of temperatures, typically from -10° C to 110° C, and is used for measuring room temperature or the temperature of liquids and solids in experiments. It lacks a constriction, meaning the mercury level falls immediately after it is removed from the substance. In contrast, a clinical thermometer has a much narrower range, usually 35° C to 42° C, specifically suited for measuring human body temperature. It features a constriction near the bulb, which prevents the mercury from dropping quickly, allowing for an accurate reading after it’s removed from the patient.

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A laboratory thermometer consists of a thin glass bulb at one end, filled with mercury, connected to a very fine glass tube called a capillary tube. This capillary tube is enclosed and protected by a thicker glass tube called the stem, which features graduations (markings) typically ranging from -10° C to 110° C. When the bulb is placed in contact with an object or substance, the mercury inside expands as it absorbs heat, causing it to rise up the capillary tube. The point at which the shiny mercury thread stabilizes on the marked scale indicates the temperature of the object.

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