Name: kelvin temperature and gas thermometer standards
Uploaded: 2023-04-30T12:29:16.000Z
Duration: 1 min 22 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.13

CHEM.13.D

Gas Thermometers and the Kelvin Scale

מדחום גז מעריך טמפרטורה בהתבסס על שינויים בלחץ או בנפח של מלא הגז.
ישנם שני סוגים של מדי חום גז: נפח קבוע, ולחץ קבוע, ואת מדחום גז נפח קבוע הוא בשימוש הנרחב ביותר.
העיקרון של מדחום זה הוא כי, בנפח קבוע, הלחץ של גז עולה ככל שהטמפרטורה עולה.
כדי לכייל את מדחום הגז, נמדד הלחץ ב 0 ו 100 מעלות צלזיוס.
ערכים אלה משורטטים בקו ישר, אשר אקסטרפולציה כדי למצוא את טמפרטורת הלחץ אפס.
טמפרטורה זו היא נקודת האפס של סולם קלווין. זהו קנה המידה הסטנדרטי לטמפרטורה, שכן יחידת SI של הטמפרטורה היא קלווין.
אפס מוחלט הוא הטמפרטורה הנמוכה ביותר האפשרית המשקפת באופן אידיאלי את היעדר מוחלט של אנרגיה תרמית.
בסולם קלווין, נקודת הקיפאון של המים היא 273.15, בעוד שנקודת הרתיחה היא 373.15. ההבדל זהה לזה שבסולם צלזיוס; רק נקודת האפס שונה.
לפיכך, ניתן לקבוע בקלות את הקשר בין סולמות קלווין וצלזיוס.

<ol>
	<li>OpenStax. (2019). פיזיקה אוניברסיטאית כרך 2. [גרסת אינטרנט]. מקור: <a href="https://openstax.org/books/university-physics-volume-2/pages/1-2-thermometers-and-temperature-scales">https://openstax.org/books/university-physics-volume-2/pages/1-2-thermometers-and-temperature-scales</a></li>
</ol>

מדחום גז וסולם קלווין

<div style="direction:rtl">ההגדרה של טמפרטורה במונחים של תנועה מולקולרית מציעה שתהיה הטמפרטורה הנמוכה ביותר האפשרית, שבה האנרגיה הקינטית הממוצעת של מולקולות היא אפס (או המינימום המותר על ידי מכניקת הקוונטים). ניסויים מאשרים את קיומה של טמפרטורה כזו, הנקראת אפס מוחלט. סולם טמפרטורה מוחלט הוא כזה שנקודת האפס שלו היא אפס מוחלט. סולמות כאלה נוחים במדע מכיוון שמספר כמויות פיזיקליות, כגון נפח גז אידיאלי, קשורות ישירות לטמפרטורה המוחלטת. סולם קלווין הוא סולם הטמפרטורה המוחלט שנמצא בשימוש נפוץ במדע. סולם קלווין הוא חלק ממערכת היחידות SI, כך שהגדרתו בפועל מסובכת יותר מזו שניתנה לעיל. ראשית, הוא אינו מוגדר במונחים של נקודות הקפאה ורתיחה של מים, אלא במונחים של נקודת משולשת. הנקודה המשולשת היא השילוב הייחודי של טמפרטורה ולחץ שבו קרח, מים נוזליים ואדי מים יכולים להתקיים ביציבות. הטמפרטורה המשולשת מוגדרת כ-273.16 K. להגדרה זו יש יתרון שלמרות שטמפרטורת ההקפאה וטמפרטורת הרתיחה של המים תלויות בלחץ, יש רק טמפרטורת משולשת אחת. אפילו עם נקודות מוגדרות היטב על הסולם, מדי חום שונים נותנים תוצאות שונות במקצת עבור טמפרטורות אחרות. לכן, יש צורך במדחום סטנדרטי. מטרולוגים בחרו את מדחום הגז בנפח קבוע למטרה זו. כלי בעל נפח קבוע מלא בגז נתון לשינויי טמפרטורה, והטמפרטורה הנמדדת פרופורציונלית לשינוי בלחץ. התוצאות תלויות במידה מסוימת בבחירת הגז, אך ככל שהגז בנורה פחות צפוף, כך התוצאות עבור גזים שונים מתאימות יותר. אם מבצעים אקסטרפולציה של התוצאות לצפיפות אפס, התוצאות מתאימות למדי, כאשר לחץ אפס מתאים לטמפרטורה של אפס מוחלט. מדי חום גז בנפח קבוע הם גדולים ומגיעים לשיווי משקל לאט, ולכן הם משמשים בעיקר כסטנדרטים לכיול מדי חום אחרים.</div>

הגדרת הטמפרטורה במונחים של תנועה מולקולרית מציעה כי צריכה להיות הטמפרטורה הנמוכה ביותר האפשרית, שבה האנרגיה הקינטית הממוצעת ...

Education

JoVE Core

Physics

פיזיקה

Unit 1

יחידה 1

Temperature and Heat

טמפרטורה וחום

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

kelvin temperature and gas thermometer standards

Kelvin temperature is the absolute scale used in science, and it starts at absolute zero. That zero point matches the lowest possible temperature, where molecular motion reaches zero or the minimum allowed by quantum mechanics. Scientists use this scale because some physical quantities, such as the volume of an ideal gas, depend directly on absolute temperature.

The Kelvin scale is part of the SI system of units, so its definition is more precise than simply using water’s freezing and boiling points. Instead, it is tied to the triple point of water. The triple point is the only temperature and pressure combination where ice, liquid water, and water vapor can all coexist. Its temperature is defined as 273.16 K, which is useful because it does not change with pressure the way water’s freezing and boiling points do.

Even with fixed reference points, different thermometers can give slightly different readings for other temperatures. For that reason, scientists need a standard thermometer. Metrologists use the constant-volume gas thermometer for this job. In this device, a gas in a sealed vessel stays at the same volume while temperature changes, and the temperature is found from the change in pressure.

The choice of gas can affect the results a little. However, the less dense the gas in the bulb, the better different gases agree. When the results are extrapolated to zero density, they match well, and zero pressure corresponds to absolute zero. Constant-volume gas thermometers are large and slow to reach equilibrium, so they are mainly used as standards to calibrate other thermometers.

Kelvin Temperature and Gas Thermometer Standards

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Kelvin temperature is the absolute scale used in science, and it starts at absolute zero. That zero point matches the lowest possible temperature, where molecular motion reaches zero or the minimum allowed by quantum mechanics. Scientists use this scale because some physical quantities, such as the volume of an ideal gas, depend directly on absolute temperature. The Kelvin scale is part of the SI system of units, so its definition is more precise than simply using water’s freezing and boiling...

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Radiation heat transfer depends on temperature, surface area, and emissivity. The Stefan-Boltzmann law describes the rate of heat transfer by emitted radiation. In this law, σ is the Stefan-Boltzmann constant, A is the object’s surface area, and T is its temperature in kelvins. The fourth-power dependence on absolute temperature makes radiation highly sensitive to small temperature changes. Even a slight rise in temperature can change the emitted heat a lot. That sensitivity is why radiation...

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Learn how the Kelvin scale is tied to absolute zero, the triple point of water, and constant-volume gas thermometers used to calibrate other thermometers.

Kelvin Temperature and Gas Thermometer Standards | JoVE K12

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Kelvin Temperature and Gas Thermometer Standards

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