Questions
Select all true statements. The threshold of human hearing is defined as having an intensity of...

Select all true statements.

The threshold of human hearing is defined as having an intensity of exactly one W/m2.

Sound is a longitudinal wave in air.

Sound waves travel faster through gases than through solids.

The sound of a horn approaching a stationary observer will have higher frequency than the frequency of the horn at rest.   

All other variables being equal, the speed of sound in air decreases as the air temperature becomes colder.

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1. The Earth spins one full rotation every 24 hours. You, a mad scientist bent on...

1. The Earth spins one full rotation every 24 hours. You, a mad scientist bent on destroying the world, wish to make "Earth stand still" - you want to make it stop rotating. In your arsenal, you have lots and lots of rocket engines that you are free to place however you wish around the Earth. How will you arrange these rockets to stop the Earth's rotation (where will you put them, how will you orient them)? How much total thrust will you need to stop the rotation? Assume the Earth is a uniform sphere. You can find the mass and radius of the Earth, and you will need the moment of inertia through a sphere's center of mass, which you can also find on Google.

2. When an object rolls without slipping, the static friction acts antiparallel to the direction of motion. Why don't we usually worry about the (negative) work done by the static friction on the rolling body? Hint: How does the rotational work done by the static friction compare? It will help to set up an example problem and calculate the quantities explicitly to compare them.

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Concepts/Description a. Discuss the difference between internal quantum efficiency and external quantum efficiency of a LED....

Concepts/Description

a. Discuss the difference between internal quantum efficiency and external quantum efficiency of a LED.

b. Describe the operation of a photodiode

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Is there a simple derivation for the law of reflection using the integral form of Maxwell's...

Is there a simple derivation for the law of reflection using the integral form of Maxwell's equations?

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In your own words, explain what conductors and insulators are, and describe how and why they...

In your own words, explain what conductors and insulators are, and describe how and why they differ. Then explain why it is important to avoid touching live electrical wires. Provide your explanation in terms of conductors and insulators and the properties of electric circuits.

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For this problem, assume that high frequency sound waves travel through human tissue at 1500 m/s...

For this problem, assume that high frequency sound waves travel through human tissue at 1500 m/s (about the speed of sound in water).

a) Measurements of the blood flow in the ascending aorta shows a maximum speed of 92.00 cm/sec. Assuming the ultrasound frequency used is 2.000000 MHz (the paper uses 2.25 MHz), calculate the frequency as seen by the blood that is traveling toward the ultrasound transducer at 92.00 cm/s. The transducer, which both transmits and receives the sound waves, is not moving. It’s fine to use lots of significant figures here, so you can see the difference in frequency.

b)Calculate the shift in frequency for the waves received by the transducer after the waves have reflected off the flowing blood back to the transducer. The shift in frequency is the difference in frequency between the incoming and outgoing waves.

c)The transducer is then re-positioned so that the blood is flowing away from the transducer. Again, calculate the shift in frequency for the waves received by the transducer after the waves have reflected off the flowing blood back to the transducer. [

d)For (c), calculate the magnitude of the percentage difference between the incoming and outgoing frequencies. (It’s essentially the same magnitude for part (b), too, because the speed of the blood is so much smaller than the speed of sound.)

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Concepts/Descriptions: a. List the modes of interaction for photons and electron in a solid. b. Contrast...

Concepts/Descriptions:

a. List the modes of interaction for photons and electron in a solid.

b. Contrast spontaneous emission and spontaneous emission of photons

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Air at 15°C flows at 9 m/s parallel to a thin flat plate measuring 260 mm...

Air at 15°C flows at 9 m/s parallel to a thin flat plate measuring 260 mm × 390 mm. The direction of flow is parallel to the 260-mm edges. The surface of the plate is at a uniform temperature of 85°C. The plate is in a large chamber with walls at a temperature of 22°C. The emissivity of the plate’s surfaces is 0·75. (a) Determine the rate of convective heat transfer from one side of the plate to air. [16] (b) Determine the rate of radiant heat transfer from one side of the plate the chamber walls. [4] (c) In the configuration described above, consider two values of freestream air speed: 9 m/s and 100 m/s. Sketch a graph showing the variation of local heat flux q'' (x) as a function of distance x along the plate from the leading edge for each value of speed, showing the two curves on a single set of axes. It is not necessary to calculate values for q'' (x) but you should determine the correct shape of each curve. Briefly explain the reasons for differences between the curves.

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A thin uniform disk of radius r and mass m is spinning about its center at...

A thin uniform disk of radius r and mass m is spinning about its center at angular speed ω0. The disk is placed flat on a horizontal surface. The coefficient of kinetic friction between the disk and the surface is μ and constant for the entire area of contact. a) Find the frictional torque on the disk. (Hint: Divide the disk into many concentric rings.) b) How long will it take the disk to come to rest?

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Thermodynamics: State the three Laws of Thermodynamics and explain their meanings.

Thermodynamics: State the three Laws of Thermodynamics and explain their meanings.

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Derive the density of states for free electrons as a function of energy E in 1)...

Derive the density of states for free electrons as a function of energy E in 1) one-dimension, 2) twodimension, and 3) three-dimension (N=total number of electrons, m=electron mass, V=volume of solid) (Hint: First, derive the total number of electrons as a function of k)

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What are incident neutrons??

What are incident neutrons??

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Modern versus classical Sport What role does techonolgy play in modern sport? Give an example of...

Modern versus classical Sport

What role does techonolgy play in modern sport? Give an example of modern sport that relies on technology and speculate on the historical beginnings of that particular sport before such technology.

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An electrical machine dissipates 2.5 kW. All cooling of the unit takes place through one exposed...

An electrical machine dissipates 2.5 kW. All cooling of the unit takes place through one exposed surface, measuring 120 mm × 190 mm. All other surfaces of the unit are insulated. 50 fins are mounted on the exposed surface. The fins are made of aluminium alloy 2024-T6, and each one measures 120 mm × 2 mm in cross-section and 80 mm in length (normal to the surface they are mounted on). The fins and base surface are exposed to fan-driven air at 15°C with a convection heat transfer coefficient of 60 W m–2 K–1. Calculate the steady-state temperature of the power supply’s exposed surface. (b) To increase the heat transfer rate through a set of fins, without changing the base temperature, would it be more effective to increase the number of fins by 20%, or to increase the length of each fin by 20%? Explain your answer.

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How does Shallow Trench Isolation cause compression in the island structure silicon?

How does Shallow Trench Isolation cause compression in the island structure silicon?

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