Photoelectric Effect: A metal surface has a work function of 2.50 eV. What is the longest wavelength of light that will eject electrons from the surface of this metal? (1 eV = 1.60 × 10-19 J, c = 3.00 × 108 m/s, h = 6.626 × 10-34 J ? s)
Fill in the blank(s) with the appropriate word(s).
497 nm
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A string is stretched and fixed at both ends, 200 cm apart. If the density of the string is 0.015 g/cm, and its tension is 600 N, what is the wavelength (in cm) of the first harmonic?
a. 600 b. 400 c. 800 d. 1 000 e. 200
Water flowing through a pipe is heated by steam condensing on the outside of the pipe. (a) Assuming a uniform overall heat transfer coefficient along the pipe, derive an expression for the water temperature as a function of distance from the entrance. (b) For an overall heat transfer coefficient of 570 W/(m2 K), based on the inside diameter of 5 cm, a steam temperature of 104°C, and water-flow rate of 0.063 kg/s, calculate the length required to raise the water temperature from 15.5 to 65.5°C.
GIVEN
• Water flowing through a pipe steam condensing on the outside
FIND
(a) An expression for the water temperature as a function of distance from the entrance, Tw (x)
(b) For Overall heat transfer coefficient (U) = 570 W/(m2 K)
Inside diameter (D) = 5 cm = 0.05 m
Steam temperature (Ts) = 104°C
Water flow rate ( m w) = 0.063 kg/s
Water temperatures: Tw,in = 15.5°C Tw,out = 65.5°C
Find the length (L) required
ASSUMPTIONS
• A uniform overall heat transfer coefficient
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at the mean temperature of 40°C (cpw) =4175 J/(kg K)
A torque acting on an object tends to produce
A) equilibrium. B) rotation. C) linear motion. D) velocity. E) a center of gravity.
The earliest human culture, involving villages and a sense of history, developed
A) about 10,000 years ago. B) about one billion years ago. C) a few million years ago. D) 100,000 to 200,000 years ago. E) about 1000 years ago.