Chapter 1: Q 1.5. (page 5)
When you're sick with a fever and you take your temperature with a thermometer, approximately what is the relaxation time?
Short Answer
1 minute.
Chapter 1: Q 1.5. (page 5)
When you're sick with a fever and you take your temperature with a thermometer, approximately what is the relaxation time?
1 minute.
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Get started for freeThe Fahrenheit temperature scale is defined so that ice melts at 320 F and water boils at 2120 F.
(a) Derive the formula for converting from Fahrenheit to Celsius and back
(b) What is absolute zero on the Fahrenheit scale?
In analogy with the thermal conductivity, derive an approximate formula for the viscosity of an ideal gas in terms of its density, mean free path, and average thermal speed. Show explicitly that the viscosity is independent of pressure and proportional to the square root of the temperature. Evaluate your formula numerically for air at room temperature and compare to the experimental value quoted in the text.
Two identical bubbles of gas form at the bottom of a lake, then rise to the surface. Because the pressure is much lower at the surface than at the bottom, both bubbles expand as they rise. However, bubble A rises very quickly, so that no heat is exchanged between it and the water. Meanwhile, bubble B rises slowly (impeded by a tangle of seaweed), so that it always remains in thermal equilibrium with the water (which has the same temperature everywhere). Which of the two bubbles is larger by the time they reach the surface? Explain your reasoning fully.
Pretend that you live in the th century and don't know the value of Avogadro's number* (or of Boltzmann's constant or of the mass or size of any molecule). Show how you could make a rough estimate of Avogadro's number from a measurement of the thermal conductivity of gas, together with other measurements that are relatively easy.
For a solid, we also define the linear thermal expansion coefficient, α, as the fractional increase in length per degree:
(a) For steel, α is 1.1 x 10-5 K-1. Estimate the total variation in length of a 1 km steel bridge between a cold winter night and a hot summer day.
(b) The dial thermometer in Figure 1.2 uses a coiled metal strip made of two different metals laminated together. Explain how this works.
(c) Prove that the volume thermal expansion coefficient of a solid is equal to the sum of its linear expansion coefficients in the three directions β=αx + αy + αz. (So for an isotropic solid, which expands the same in all directions, β =3 α .)
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