Which of the following wavelengths could NOT be present as a harmonic on a 2 m long string?
a. 4 m
b. 2 m
c. 1 m
d. 0.89 m
e. 0.5 m
d
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A 2.5 × 2.5 m steel sheet 1.5-mm-thick is removed from an annealing oven at a uniform temperature of 425°C and placed in a large room at 20°C in a horizontal position. (a) Calculate the rate of heat transfer from the steel sheet immediately after its removal from the furnace, considering both radiation and convection. (b) Determine the time required for the steel sheet to cool to a temperature of 60°C. Hint: This will require numerical integration.
GIVEN
• Horizontal steel sheet in air
• Sheet dimensions = 2.5 m × 2.5 m × 0.0015 m
• Sheet initial temperature (Tsi) = 425°C = 698 K
• Air temperature (T?) = 20°C = 293 K FIND
(a) The initial rate of heat transfer (q) (b) The time required for the sheet to cool to 60°C (333 K)
ASSUMPTIONS
• The room behaves as a black body at T?
• The steel sheet behaves as a black body (? = 1.0)
• Heat transfer takes place from both top and bottom of the sheet
• The steel is 1% carbon steel
• Heat transfer from the edges of the plate is negligible
SKETCH
PROPERTIES AND CONSTANTS
The Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)
for 1% carbon steel
Specific heat (cs) = 473 J/(kg K)
Density (?s) = 7801 kg/m3
for dry air at the mean temperature of 496 K (223°C)
Thermal expansion coefficient (?) = 0.00203 1/K
Thermal conductivity (k) = 0.0384 W/(m K)
Kinematic viscosity (?) = 38.7 × 10–6 m2/s
Prandtl number (Pr) = 0.71
A block of wood with a piece of iron tied to the top of it floats in a bucket of water. If the wood and iron are turned over so that the iron is submerged beneath the wood, the water level at the side of the bucket
A) rises. B) falls. C) remains the same.
Which force field can increase a moving electron's speed?
A) electric field B) magnetic field C) both of these D) neither of these
A galvanometer has a coil with a resistance of 24.0 ?, and a current of 180 ?A causes it to deflect full scale. If this galvanometer is to be used to construct an ammeter that can read up to 10.0 A, what shunt resistor is required?
A) 123 µ? B) 234 µ? C) 342 µ? D) 432 µ? E) 423 µ?