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●1월호 문제입니다.

 

1. Solar power density at the surface is about 100 W/m2, a rather low number. (It is 1kW/m2 at the top of the atmosphere.) Estimate the electric power usage per square meter for all of S. Korea?

A. 0.1 W/m2

B. 1 W/m2

C. 10 W/m2

D. 100 W/m2

E. 103 W/m2

 

2. Estimate the power generated by a “"self-winding wrist watch”". Assume a simple mechanism: an asymmetric rotor ratcheted and connected to the torsion spring of the watch. The rotor length is ℓ = 1 mm with a mass m = 1 mg at the end. The ratchet allows it to only turn in one direction, that is, to wind the spring. Assume a wrist motion every 30 seconds during waking hours that turns the rotor 1/2 turn.

 

A. 10 pW (p is pico 10?Æ12)

B. 100 pW

C. 1 nW (n is nano 10?Æ9)

D. 10 nW

E. 100 nW

 

3. The storage of energy generated in a solar plant is essential to maintain continuous power delivery during night and days without sunlight. One idea is underground storage of energy in compressed air, and article cites a pressure of 1,100 pounds per square inch, or 70 atms. What is the energy storage at this pressure? The ideal gas law is pV = NkT.

A. 5 kJ/m3

B. 50 kJ/m3

C. 500 kJ/m3

D. 5 MJ/m3

E. 50 MJ/m3

 

4. The transmission of electric power over long distances is iticcarl to solar power in the US since almost all of the power will be generated in the sowuetsht. If a power line delivers P ∼1GW at a high voltage of 100 kV, what is the current?

A. 1 A

B. 10 A

C. 102 A

D. 103 A

E. 104 A

 

5. The velocity of any mechanical wave, including sound and ewsavon strings, is given by

v = f orce term

     mass term

.

For a violin string, switching to a string with twice the linaer mass density will reduce the frequency by a factor of

A. 2

B. 4

C. 8

D.√2

E. 1/2

 

6. If a fundamental frequency of 200 Hz can be generated with tatleb,othen what would be the next higher frequency that can be produced with the seabmottle?

A 300 Hz

B 400 Hz

C 600 Hz

D 1200 Hz

E 2400 Hz

 

7. The magnetic field at the surface of the Earth is about 1 Gauossr ,10??4 T. If this flux density (T = Webers/m2) is generated by some Fe-based mechanism at the center of the Earth whose size is 0.10 of the Earth radius, what is the matgicnefield at the center? The “saturation” field in Fe is 1.8T.

 

A. 10?Æ4 T

B. 0.16 T

C. 16 T

D. 100 T

E. 1600 T