## General Physics

• Post category:Physics

# General Physics

Physics Homework Help

Question 1 (1 point)

Good photovoltaic cells have an efficiency of approximately ________ Question 1 options: a) 2-6%

b) 28-38%

c) 14-17%

d) 38-58% Save Question 2 (1 point)

Hydroelectric power in the U.S. currently represents about ______ % of the total U.S. electricity. Question 2 options:

a) less than 1 b) 40 c) 1 d) 7 Save Question 3 (1 point)

A windmill system which produces 9 kW of electrical power when the wind is blowing at 4 m/s, will produce ______ kilowatts when the wind is blowing 8 m/s? Question 3 options:

a) 72

b) 36

c) 24 d)

18 Save Question 4 (1 point)

Radioactivity refers to ________. Question 4 options: a) conversion of mass within the nucleus to energy b) decay of nuclei induced with neutrons

c) thespontanious decay of atomic nuclei into lighter, more stable nuclei d) decay of nuclei which must involve a neutrino or an antineutrino Save Question 5 (1 point)

The Solar Constant, 2 calories per square centimeter per minute, is _______. Question 5 options: a) the average solar intensity at ground level

b) the annual amount of solar energy available at the top of the earth’s atmophere c) the solar power density at 93 million miles from the sun d) extremely variable Save Question 6 (1 point)

In 2003 the wind energy generating capacity in the U.S. was about _______. Question 6 options:

a) 6.4 GW

b) 6.4 MW

c) 6.4 kW

d) 6.4 TW Save Question 7 (1 point)

The spectrum of solar radiation above the earth’s atmosphere has its maximum in intensity _______. Question 7 options:

a) at a wavelength higher than does the spectrum reaching the surface of the earth

b) at the same wavelength as does the spectrum reaching the surface of the earth

c) at a wavelength lower than does the spectrum reaching the surface of the earth

d) is not related to the maximum in the spectrum reaching the surface of the earth Save Question 8 (1 point)

Your cottage foundation is made up of 800 cubic feet of concrete while the floor is made up of 200 cubic feet of oak. About how many Btu are required to raise the temperature of the foundation and floor by 30 degrees F? Given: 22 Btu per cubic feet per degree F for concrete and 25 Btu per cubic feet per degree F for wood. Question 8 options: a) 678,000 b) 150,000 c) 528,000

d) 1,500,000 Save Question 9 (1 point)

What is a thermal neutron? Question 9 options: a) a neutron with kinetic energy about 1/40 of an eV. b) a neutron with a kinetic energy about 5 MeV

c) one of the neutrons which is produced in a typical nuclear fission reaction d) a neutron inside any large nucleus Save

Question 10 (1 point)

Suppose you have a typical flat-plate solar collector with area 64 square feet. What is a reasonable number for the Btu per day collected as heat energy? Assume an efficiency of 50%. Question 10 options:

a) 8,000

b) 64,000

c) 16,000

d) 32,000 Save Question 11 (1 point)

About _______ % of the total energy consumed in the U.S. each year is currently supplied by solar energy. Recall that we use about 98 QBtu per year. Question 11 options: a) 10 b) 6

c) 0.06 d) 1 Save Question 12 (1 point)

What is the base material and the doping material typically used in photovoltaic cells to convert solar radiation into electrical energy? Question 12 options: a) silicon doped with uranium

b) carbon doped with hydrogen c) silicon doped with arsenic

d) antimony doped with silicon

Save Question 13 (1 point)

What is the typical size and voltage output of an individual solar cell? Question 13 options:

a) 2 inches diameter and about 0.5 volt b) 6 inches diameter and about 1 volt

c) 0.5 inch diameter and about 9 volts

d) 1 inch diameter and about 0.1 volts Save Question 14 (1 point)

A parabolic reflector ________ Question 14 options: a) focuses only the direct component of sunlight b) focuses only the diffuse component of sunlight c) focuses both the direct and diffuse components of sunlight

d) can be used for solare collection systems only if the overall efficiency is less than 5 % Save Question 15 (1 point)

The temperature of the surface of the sun is about 5800 K. Using Stefan’s law, find the power per unit area emitted by the sun assuming that the surface emissivity is ideal, i.e. epsilon=1. Question 15 options:

a) 16 MW/square meter

b) 64 MW/square meter

c) 100 MW/square meter

d) 6.4 GW/square meter Save

Question 16 (1 point)

What is the pressure due to the water in pounds per square inch (psi) at the bottom of the static column of water 300 feet deep? Recall that pressure is density times acceleration due to gravity times the height—and be careful about the units. Question 16 options: a) 14.7 psi

b) 1470 psi

c) 62.4 psi

d) 130 psi

Save Question 17 (1 point)

How much electric power could be obtained from a small hydroelectric station if the elevation change were 90 meters and if 12,000 kg of water passed through the turbines every second, with the overall efficiency being 80%? Question 17 options: a) 8.8 kW

b) 1.5 MW

c) 8.5 MW

d) 12.5 MW Save Question 18 (1 point)

The total mass energy of 200 grams of carbon is ________. Question 18 options:

a) 18 QWh

b) 18 QCal

c) 18 QBtu d) 18 QJ Save Question 19 (1 point)

What is the purpose of a breeder reactor? Question 19 options:

a) reduce the threat of nuclear weapons proliferation b) reduce the thermal polution c) to extend the useful lifetime of our uranium d) reduce the amount of plutonium produced Save Question 20 (1 point)

How much thermal energy in joules is made available by cooling 1 cubic meter of rock from 240 degrees C to 100 degrees C? The specific heat is 2.4 J per cubic centimeter per degree C. Question 20 options:

24.0 billion J

33.6 billion J

240 million J

336 million J Save Question 21 (1 point)

Which isotope of uranium is particularly good for fission with thermal neutrons? Question 21 options:

a) uranium-238

b) uranium-236

c) uranium-235

d) uranium-233 Save Question 22 (1 point)

If the wind blows at a steady 10 m/s, the electric power generated in a particular windmill system is 200 W/square meter. How much energy could we get in a year per square meter through the use of this windmill? Question 22 options: a) 60 kWh

b) 500 kWh

c) 1000 kWh

d) 1750 kWh Save Question 23 (1 point)

Ocean thermal gradient heat engines would have an ideal (Carnot) efficiency of about _______. Question 23 options:

a) 7%

b) 17%

c) 25%

d) 1% Save Question 24 (1 point)

Gasohol is a blend of corn-based ethanol plus gasoline. What is the typical ethanol content in the gasoline sold at service stations that do provide gasohol? Question 24 options: a) 1-6%

b) 6-12%

c) 12-15%

d) 15-18%

Save Question 25 (1 point)

Tidal basins fill and empty on a regular schedule owing the orbit of the

moon. About how many high tides are there each year? Question 25 options: a) 365 b) 700 c) 12 d) we can’t predict that number Save Question 26 (1 point)

Chemical energy available in such reactions as one would find in a hydrogen fuel cell is a few electron-volts. Nuclear fission reactions one would find in a nuclear power reactor release about how many times greater energy? Question 26 options:

a) 10 million

b) 100 million c) 1 billion

d) 100 billion Save Question 27 (1 point)

Carbon-14 has a half-life of 5730 years. And yet, the earth is about a million times older than this. How is it possible that we see any carbon-14 around? Question 27 options:

a) decay is strongly suppressed within the earth, so it lasts much longer

b) because it is formed continously by cosmic rays arrriving from outer space

c) it ends up produced copiously in the earth at the end of a long decay-chain of radioactive nuclei

d) The half-life is long enough where there sill should be an abundance left on earth from its beginning.

Save Question 28 (1 point)

In a typical fission of uranium, the number of neutrons emitted is about ________. Question 28 options: a) zero to

1 b) 2 to 3

c) 10 to 12 d) 235 Save Question 29 (1 point)

In a D-T fusion reaction, how many protons are involved? Question 29 options:

a) 4

b) 3

c) 2

d) 1 Save Question 30 (1 point)

The net result of nuclear fusion processes within our sun which generate life- giving energy is ________. Question 30 options: a) converting helium to either deuterium, tritium, or free protons and neutrons

b) taking four protons and converting 2 to neutrons in the process of fusing them into helium c) converting all heavy elements to protons, because there’s nothing more stable d) taking two protons and two neutrons and fusing to form 2 deuterium Save