A circuit consists of N resistors, all of resistance R, connected as shown below. A potential difference V is applied to the circuit. The equivalent resistance of the circuit is
a.
.
b.
b
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In a long, 30-cm square bar shown in the accompanying sketch, the left face is maintained at 40°C and the top face is maintained at 250°C. The right face is in contact with a fluid at 40°C through a heat transfer coefficient of 60 W/(m2 K) and the bottom face is in contact with a fluid at 250°C through a heat transfer coefficient of 100 W/(m2 K). If the thermal conductivity of the bar is 20 W/(mK), calculate the temperature at the 9 nodes shown in the sketch.
GIVEN
• Square bar with two surfaces at fixed temperature and two surfaces with convective boundary conditions
FIND (a) Temperature at 9 shown nodes
SKETCH
Atmospheric pressure air is heated in a long annulus (25-cm-ID, 38-cm-OD) by steam condensing at 149°C on the inner surface. If the velocity of the air is 6 m/s and its bulk temperature is 38°C, calculate the heat transfer coefficient.
GIVEN
Atmospheric flow through an annulus with steam condensing in inner tube
Inside diameter (Di) = 25 cm = 0.25 m
Outside diameter (Do) = 38 cm = 0.38 m
Steam temperature (Ts) = 149°C
Air velocity (V) = 6 m/s
Air bulk temperature (Tb) = 38°C
FIND
The heat transfer coefficient (hc)
ASSUMPTIONS
Steady state
Steam temperature is constant and uniform
Heat transfer to the outer surface is negligible
Air temperature given is the average air temperature
Thermal resistance of inner tube wall and condensing steam is negligible (Inner tube wall surface
temperature = Ts)
SKETCH
PROPERTIES AND CONSTANTS
for dry air at 38°C
Three pith balls supported by insulating threads hang from a support. We know that ball X is positively charged. When ball X is brought near balls Y and Z without touching them, it attracts Y and repels Z. Since pith is an insulating material, we can conclude that
a. Y has a negative charge. b. Z has a negative charge. c. Y has a positive charge. d. Z has a positive charge. e. Z is neutral (has no net charge).
The huge, dark, almost spherical regions between the superclusters of galaxies are called ________
Fill in the blank(s) with correct word