An electric current can consist of
a. positive ions flowing in a liquid. b. negative ions flowing in a liquid.
c. electrons flowing in a wire. d. all of the above.
d
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Which of the following is an inherent disadvantage of radio telescopes?
A. Radio telescopes cannot detect visible light. B. They only work at night. C. Radio telescopes have low magnification. D. Radio signals are very weak, and their photons do not penetrate the atmosphere easily. E. The long wavelength of radio waves results in lower resolving power, compared to other telescopes of the same size.
What did the Martian surface look like from the Viking lander sites?
A) a dry, dusty, boulder-strewn desert B) a huge canyon stretching out to the horizon C) flat, dark volcanic rocks out to the horizon D) very mountainous with huge volcanoes in the distance
The heat loss from the hairdryer duct enclosure was neglected. To a designer, while this may appear to be reasonable assumption it should really be checked bu order of magnitude calculations even if all the parameters are not known. In order to determine whether the heat loss from the exterior of the duct enclosure is neglected or not, assume a high surface emissivity of 0.8, an average surface temperature of 400C, and consider an estimate for natural convection coefficient at a high reasonable value. If the length of hair dryer is 20 cm, calculate the expected heat loss per unit length of the dryer duct, compare it with heat dissipation per unit length from the internal electrical heating, and comment on validity of negligible heat loss assumption.
GIVEN - High surface emissivity of 0.8, an average surface temperature of 400C - Length of the hear drier L=20 cm =0.2 m FIND - Expected heat loss per unit length of dryer duct - Compare it with heat dissipation per unit length from the internal electrical heating. ASSUMPTIONS - Steady state conditions prevail - Heat loss from outside of dryer duct is neglected. PROPERTIES AND CONSTANTS the air properties are Convection heat transfer coefficient for air (considering higher value) (hc)=20 W/(m2 K) Specific heat capacity(Cp)= 1.0049 kJ/kgK
Drag forces in cars depend on the profile the car offers to the air
What will be an ideal response?