The heater element of a particular 120-V toaster is a 8.9-m length of nichrome wire, whose diameter is 0.86 mm. The resistivity of nichrome at the operating temperature of the toaster is 1.3 × 10-6 ? ? m
If the toaster is operated at a voltage of 120 V, how much power does it draw? A) 720 W
B) 700 W
C) 750 W
D) 770 W
E) 800 W
A
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A stainless steel pin fin 5-cm-long, 6-mm-OD, extends from a flat plate into a 175 m/s air stream as shown in the sketch. Estimate (a) the average heat transfer coefficient between air and the fin. (b) the temperature at the end of the fin. (c) the rate of heat flow from the fin with glycerol at 20°C flowing over the fin at 2 m/s. The plate temperature is 50°C.
GIVEN
• A stainless steel pin fin in an air stream
• Pin length (L) = 5 cm = 0.05 m
• Pin diameter (D) = 6 mm = 0.006 m
• Glycerol velocity (U?) = 2 m/s
• Glycerol temperature (T?) = 20°C
• Plate temperature (Tp) = 50°C FIND
(a) The average heat transfer coefficient ( h c) (b) The temperature of the end of the fin (TL) (c) The rate of heat flow from the fin (qf) ASSUMPTIONS
• Steady state
• Turbulence in the glycerol approaching the fin is low
• Radiative heat transfer is negligible
• Steel is type 304
• Steel properties are uniform
• Variation of the thermal properties of glycerol and steel with temperature is negligible
PROPERTIES AND CONSTANTS
Thermal conductivity (k) = 0.285 W/(m K) Kinematic viscosity (?) = 1175 × 10–6 m2/s Prandtl number (Pr) = 12,609 for type 304 stainless steel ks = 14.4 W/(m K) at 20°C
Consider the sun and its largest planet Jupiter. On the line joining them, how far from the center of the sun is their center mass? Is it within or outside the sun? (Jupiter-sun distance is 778 × 106 km, diameter of the sun is 1
4 × 106 km, the sun is 1000 times as massive as Jupiter)
All real images
a. cannot be focused on a screen. b. are erect. c. can be focused on a screen. d. are inverted.
Elliptical galaxies contain more gas, dust, and young stars than do Sa galaxies
a. True b. False Indicate whether the statement is true or false