In an RC circuit, how many time constants must elapse if an initially uncharged capacitor is to reach 80% of its final potential difference?
A. 2.2
B. 1.9
C. 1.6
D. 3.0
E. 5.0
Answer: C
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An electron is in an infinite square well that is 2.6 nm wide. What is the smallest value of the state quantum number n for which the energy level exceeds 100 eV? (h = 6.626 × 10-34 J ? s, mel = 9.11 × 10-31 kg, 1 eV = 1.60 × 10-19)
A) 43 B) 44 C) 45 D) 42 E) 41
To determine the thermal conductivity of a long, solid 2.5 cm diameter rod, one half of the rod was inserted into a furnace while the other half was projecting into air at 27°C. After steady state had been reached, the temperatures at two points 7.6 cm apart were measured and found to be 126°C and 91°C, respectively. The heat transfer coefficient over the surface of the rod exposed to the air was estimated to be 22.7 W/(m2 K). What is the thermal conductivity of the rod?
GIVEN
FIND
The thermal conductivity (k) of the rod
ASSUMPTIONS
Uniform thermal conductivity
One dimensional conduction along the rod
The rod approximates a fin of infinite length protruding out of the furnace
SKETCH
In ultrasound the __________ of the sound is much greater than in normal sound
Fill in the blank(s) with correct word
What was Cecilia Payne's discovery?
A. She showed how to calculate the level in which an atom's electrons were most likely to be found. B. She proved that stars are composed mainly of hydrogen. C. She classified stellar spectra by temperature. D. All of these choices are correct.