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what temperature do the following pairs of scales read the same, if ever: (a) Fahrenheit and Celsius (verify the listing in Table \(19-1\) ), (b) Fahrenheit and Kelvin, and (c) Celsius and Kelvin?

Short Answer

Expert verified
Celsius and Fahrenheit are equal at -40 degrees; Kelvin and Fahrenheit match at 574.585 K. No point exists where Celsius and Kelvin match in the same scale.

Step by step solution

01

Setup the equations

To find when two temperature scales read the same, set their formulas equal to each other. Use the following equations:1. Fahrenheit and Celsius: \( F = \frac{9}{5}C + 32 \).2. Fahrenheit and Kelvin: \( F = \frac{9}{5}(K - 273.15) + 32 \).3. Celsius and Kelvin: \( C = K - 273.15 \).
02

Solve the equations

Now solve the above equations for equality:(a) Fahrenheit and Celsius:Set \( F = C \)\( C = \frac{9}{5}C + 32 \);Reorganize to find the value of C that satisfies this equation.(b) Fahrenheit and Kelvin:Set \( F = K \)\( K = \frac{9}{5}(K - 273.15) + 32 \);Reorganize to find the value of K that satisfies this equation.(c) Celsius and Kelvin:Set \( C = K \)\(C = K - 273.15 \);Reorganize to find the value of C or K that satisfies this equation.
03

Calculate the temperatures

(a) Fahrenheit and Celsius:\( C = \frac{9}{5}C + 32 \);\( C - \frac{9}{5}C = 32 \);\( \frac{-4}{5}C = 32 \);\( C = -40 \);So at -40 degrees, Celsius and Fahrenheit are the same.(b) Fahrenheit and Kelvin:\( K = \frac{9}{5}(K - 273.15) + 32 \);Rearrange to \( K = 1.8 K - 491.67 + 32 \);\( K - 1.8 K = -459.67 \);\( -0.8 K = -459.67 \);\( K = 574.585 \);(c) Celsius and Kelvin:\( C = K - 273.15 \);Set C = K,\( K - 273.15 = K \);Not possible since this leads to no solution with finite temperature value where C = K in the common scale.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Fahrenheit and Celsius Equivalence
Understanding the point where Fahrenheit and Celsius scales read the same can be a bit tricky, but it's a fascinating concept. First, remember the formula to convert Celsius to Fahrenheit: ewline $$ F = \frac{9}{5}C + 32 $$To find the temperature where both scales equate, we set $$ F = C $$. This gives us:
  • $$ C = \frac{9}{5}C + 32 $$
By simplifying, you get:
  • $$ C - \frac{9}{5}C = 32 $$
  • $$\frac{-4}{5}C = 32 $$
  • $$ C = -40 $$
Thus, at -40 degrees, Celsius and Fahrenheit scales are the sameThis fact means (when you see -40) both mercury and alcohol thermometers will display the same reading. It’s a useful point especially in extremely cold climates.
Fahrenheit and Kelvin Equivalence
The Fahrenheit and Kelvin scales also have an intersection point. However, this one might seem less intuitive due to their origins. To find the common reading, use the conversion formula that involves Kelvin: ewline $$ F = \frac{9}{5}(K - 273.15) + 32 $$Set $$ F = K $$ and solve:
  • $$ K = \frac{9}{5}(K - 273.15) + 32 $$
  • Rearrange: $$ K = 1.8 K - 491.67 + 32 $$
  • Simplify: $$ K - 1.8 K = -459.67 $$
  • $$ -0.8 K = -459.67 $$
  • $$ K = 574.585 $$
Hence, at approximately 574.585 Kelvin, the Fahrenheit and Kelvin scales are equal.It's a significantly high value compared to regular physical phenomena, reflecting the different ideals these scales are based upon:
  • The Kelvin scale is absolute, starting from absolute zero.
  • The Fahrenheit scale is more conventional and practical in everyday usage.
Celsius and Kelvin Equivalence
When considering the Celsius and Kelvin scales, it’s important to note their direct relationship:ewline $$ C = K - 273.15 $$We naturally assume they might meet at a certain temperature. But substituting $$ C = K $$ reveals a contradiction:
  • $$ C = K - 273.15 $$
  • Set $$ C = K $$: $$ K = K - 273.15 $$
  • Simplifying, we see this equation leads to a false statement.
Therefore, Celsius and Kelvin scales never meet on a numerical plane.Yet, this intimacy helps in understanding both:
  • Kelvin essentially translates Celsius readings into absolute measurements.
  • Used often in scientific contexts because of its non-negative nature and starting from absolute zero.

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Most popular questions from this chapter

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