Inside a house, stepping on a tile floor barefooted may feel almost cold, but stepping on carpet in an adjacent room feels comfortably warm. Why is this?
a. It's because the tile is below room temperature while the carpet is at room temperature.
b. It's because the tile is at room temperature while carpet is normally warmer.
c. It's because the thermal conductivity of tile is less than that of carpet.
d. It's because the thermal conductivity of carpet is less than that of tile.
D
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In an experimental setup in a laboratory, a long cylinder with 5-m diameter, and an electrical resistance heater inside its entire length is cooled with water flowing crosswise over the cylinder at 25oC and a velocity of 0.8 m/s. For these flow conditions, 20 KW/m of power is required to maintain a uniform temperature of 95oC at the surface of the cylinder. When water is not available, air at 25oC is used with the velocity of 10 m/s to maintain the same surface temperature. However, in this case, the cylinder surface heat dissipation rate is reduced to 400 W/m. Calculate the convection heat transfer coefficients for both water and air, and comment on the reason for differences in the value.
GIVEN • A long cylinder with diameter d=5 cm=0.05 m Case A • Crosswise water flow at 25oC and velocity of 0.8 m/s • Power required(qc/L)=20,000 W/m • Surface temperature(Ts)=95 oC Case B • Crosswise air flow at 25oC and velocity of 10 m/s • Power required(qc/L)=400 W/m • Surface temperature(Ts)=95 oC FIND • Convection heat transfer coefficient for both air and water. • Comment on differences in the values. ASSUMPTIONS • The system is in steady state
Which of the following lenses is a diverging lens?
A. A B. B C. C
The ability of a telescope to separate two closely spaced stars is called ________
Fill in the blank(s) with correct word
The Curiosity rover has detected evidence of what kind(s) of chemical activity in Mars' soil?
A) organic carbon chemistry B) helium and hydrogen C) photosynthesis D) water, sulfur and chlorine-containing minerals E) minerals containing sulfur or produced by reactions with sulfuric acid