Conduction: A heat-conducting rod, 0.90 m long and wrapped in insulation, is made of an aluminum section that is 0.20 m long and a copper section that is 0.70 m long. Both sections have a cross-sectional area of 0.00040 m2. The aluminum end and the copper end are maintained at temperatures of 30°C and 230°C, respectively. The thermal conductivities of aluminum and copper are 205 W/m ? K (aluminum) and 385 W/m ? K (copper). What is the temperature of the aluminum-copper junction in the rod with steady state heat flow?
A. 100°C
B. 93°C
C. 86°C
D. 80°C
E. 74°C
Answer: A
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A 15 cm black disk is placed halfway between two black 3-m-diameter disks that are 7 m apart with all disk surfaces parallel to each other. If the surroundings are 0 K, determine the temperature of the two larger disks required to maintain the smaller disk at 540°C.
GIVEN
GIVEN
• A black disk (A1) halfway between two other black disks (A2 & A3)
• Diameter of A1 (D1) = 15 cm = 0.15 m
• Diameter of A2 and A3: (D2 = D3) = 3 m
• Distance between A2 and A3 (2L) = 7 m
• Surrounding temperature (T?) = 0 K
• Temperature of A1 (T1) = 540°C = 813 K
FIND
• The temperature A2 and A3 required ASSUMPTIONS
• A2 and A3 are at the same temperature (T2 = T3)
• Steady state conditions
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)
One mole of an ideal gas has a temperature of 25°C. If the volume is held constant and the pressure is doubled, the final temperature (in °C) will be
A. 174 B. 596 C. 50 D. 323 E. 25
What is the formula of a compound formed from the ions M3+ and X3-?
a. M2X b. MX c. M2X3 d. MX2
A straight 10-cm wire bent at its midpoint so as to form an angle of 90° carries a current of 10 A. It lies in the xy plane in a region where the magnetic field is in the positive z direction and has a constant magnitude of 3.0 mT. What is the magnitude of the magnetic force on this wire?
a. 3.2 mN b. 2.1 mN c. 5.3 mN d. 4.2 mN e. 6.0 mN