Q: A train approaches a platform at 10.0 m/s and blows its whistle. The speed of sound is $$v_\text{sound} = 331\ \text{m/s}$$ and the frequency of the whistle is $$f = 240\ \text{Hz}. $$What is the observed frequency by a stationary observer on the platform?

$$f' = f \left( \dfrac{v_\text{sound}}{v_\text{sound} - v_\text{source}} \right) = 240 \left( \dfrac{331}{331 - 10} \right) = 247.6\ \text{Hz}$$

Q: A bat uses ultrasound at a frequency of $$10\ \text{MHz} to $$locate prey. If the speed of sound in air is $$340\ \text{m/s}$$, what is the wavelength of the sound emitted by the bat?

$$\lambda = \dfrac{v}{f} = \dfrac{340}{10 \times 10^6$} = 3.4 \times 10$$^{-5}$$\ \text{m}$$

Q: Convert a temperature of $$-117\ ^\circ\text{F} to $$Kelvin using the formulas provided.

$$T[\text{K}] = \dfrac{5}{9}(-117 - 32) + 273.15 = 190\ \text{K}$$

Q: A tungsten filament inside an incandescent lightbulb operates at $$2527\ ^\circ\text{C}. $$What is its temperature in Kelvin?

$$T[\text{K}] = 2527 + 273.15 = 2800\ \text{K}$$

Q: Which equation correctly converts Celsius to Fahrenheit?

$$T[\text{F}] = \dfrac{9}{5}T[\text{C}] + 32$$

Q: A sound source emits a frequency $$f$$ and moves toward a stationary observer at speed $$v_\text{source}. $$Which formula gives the observed frequency?

$$f' = f \left( \dfrac{v_\text{sound}}{v_\text{sound} - v_\text{source}} \right)$$

Q: Which of the following is the correct definition of atomic mass unit (u)?

1 u = $$1.6605 \times 10$$^{-27}$$ kg

Question 1

A train approaches a platform at 10.0 m/s and blows its whistle. The speed of sound is $$v_	ext{sound} = 331\ 	ext{m/s}$$ and the frequency of the whistle is $$f = 240\ 	ext{Hz}. $$What is the observed frequency by a stationary observer on the platform?

Accepted Answer

$$f' = f \left( \dfrac{v_	ext{sound}}{v_	ext{sound} - v_	ext{source}} ight) = 240 \left( \dfrac{331}{331 - 10} ight) = 247.6\ 	ext{Hz}$$

Question 2

Which of the following best describes the Zeroth Law of Thermodynamics?

Accepted Answer

If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.

Question 3

A bat uses ultrasound at a frequency of $$10\ 	ext{MHz} to $$locate prey. If the speed of sound in air is $$340\ 	ext{m/s}$$, what is the wavelength of the sound emitted by the bat?

Accepted Answer

$$\lambda = \dfrac{v}{f} = \dfrac{340}{10 	imes 10^6$} = 3.4 	imes 10$$^{-5}$$\ 	ext{m}$$

Question 4

Which temperature scale is based on an absolute zero reference point?

Accepted Answer

Kelvin

Question 5

Convert a temperature of $$-117\ ^\circ	ext{F} to $$Kelvin using the formulas provided.

Accepted Answer

$$T[	ext{K}] = \dfrac{5}{9}(-117 - 32) + 273.15 = 190\ 	ext{K}$$

Question 6

Which of the following statements about thermal equilibrium is correct?

Accepted Answer

When two objects are in thermal equilibrium, there is no net heat flow between them.

Question 7

A tungsten filament inside an incandescent lightbulb operates at $$2527\ ^\circ	ext{C}. $$What is its temperature in Kelvin?

Accepted Answer

$$T[	ext{K}] = 2527 + 273.15 = 2800\ 	ext{K}$$

Question 8

Which of the following is NOT a property that can be used to define temperature?

Accepted Answer

Mass

Question 9

A jet breaks the sound barrier and creates a shock wave. What is the physical explanation for the formation of a sonic boom?

Accepted Answer

The jet travels faster than the speed of sound, causing sound waves to overlap and form a shock front.

Question 10

Which equation correctly converts Celsius to Fahrenheit?

Accepted Answer

$$T[	ext{F}] = \dfrac{9}{5}T[	ext{C}] + 32$$

Question 11

A sound source emits a frequency $$f$$ and moves toward a stationary observer at speed $$v_	ext{source}. $$Which formula gives the observed frequency?

Accepted Answer

$$f' = f \left( \dfrac{v_	ext{sound}}{v_	ext{sound} - v_	ext{source}} ight)$$

Question 12

Which of the following is the correct definition of atomic mass unit (u)?

Accepted Answer

1 u = $$1.6605 	imes 10$$^{-27}$$ kg

Question 13

Which of the following best describes Brownian motion?

Accepted Answer

Random microscopic motion of particles suspended in a fluid

Question 14

If the freezing point of water is $$0\ ^\circ	ext{C}$$, what is this temperature in Fahrenheit?

Accepted Answer

$$T[	ext{F}] = \dfrac{9}{5} 	imes 0 + 32 = 32\ ^\circ	ext{F}$$

Question 15

A stationary observer hears a frequency of $$253.1\ 	ext{Hz}$$ from a train whistle when the train is moving toward them at $$10.0\ 	ext{m/s}. $$What frequency will the observer hear when the train is at rest?

Accepted Answer

$$f = 240\ 	ext{Hz}$$

Question 16

Which of the following is NOT a correct temperature conversion formula?

Accepted Answer

$$T[	ext{C}] = \dfrac{9}{5}(T[	ext{F}] - 32)$$

Question 17

Which of the following is a real-world application of the Doppler effect?

Accepted Answer

Ultrasound imaging in medicine

Question 18

If the surface temperature of the Sun is $$6000\ 	ext{K}$$, what is this temperature in Celsius?

Accepted Answer

$$T[	ext{C}] = 6000 - 273.15 = 5726.85\ ^\circ	ext{C}$$

Lecture 26: Temperature, Gas Laws, and Applications of Sound

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