At room temperature (~295 K with kT ~ 0.025 eV), what fraction of the free electrons in a semiconductor with an energy gap of 1.5 eV can be expected to be in the conduction band?
A)
10-9
B)
10-13
C)
10-30
D)
0.03
E)
10-15
B
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Your friend applies a horizontal force to your 2.0-kg physics textbook, which rests stationary against a vertical wall. The static and kinetic friction coefficients between the book and the wall are 0.20 and 0.15, respectively. With what force must your friend push on the book in order that it doesn’t slip down the wall?
A. 39 N B. 20 N C. 19.6 N D. 25 N E. 98 N
Some regions along the plane of the Milky Way appear dark because
A) there are no stars in these areas. B) stars in that region are hidden by interstellar gas. C) stars in that region are hidden by dark dust particles. D) many brown dwarfs in those areas absorb light which they turn into heat. E) many black holes absorb all light from those directions.
Air pressure is 1.00 × 10^5 N/m2, air density is 1.30 kg/m3, and the density of soft drinks is 1.00 × 10^3 kg/m3 . If one blows carefully across the top of a straw sticking up 0.10 m from the liquid in a soft drink can, it is possible to make the soft drink rise half way up the straw and stay there. How fast must the air be blown across the top of the straw?
a. 0.036 m/s b. 27 m/s c. 1.4 m/s d. 19 m/s e. 750 m/s
The units of work are the same as those of ______________
Fill in the blank(s) with correct word