If a watt is a unit of power, how can a kilowatthour be a measure of energy? Explain
What will be an ideal response?
The watt is a unit of power, equivalent to a joule per second. Therefore, a
wattsecond is the same as a joule. One watt times 60 seconds is a wattminute, and it is 60
joules. Sixty wattminutes is a watthour, and this is then equivalent to 3600 joules. A
thousand watthours is a kilowatthour, so that is the same as 1000 (3600 joules) = 3,600,000
joules.
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A radiant heater element is made so that it is concentric about a copper tube, as shown in the figure. The heater is 1 cm thick, 10 cm OD, and 8 cm ID. The copper tubing is 4 cm in diameter, has an emissivity of 0.05, and is at 200ºC. The heater tubing has an emissivity of 0.9 on the inside, and 0.04 on the outside. The heater is at 1000ºC. If the surroundings are taken as a black body at 300 K, determine the power per unit length of the heater needed for steady state operation.
How much of the Earth's surface is experiencing night at any time?
a. less than one-half, because of the tilt of the equator to the ecliptic plane b. more than one-half, because of the precession of the poles c. exactly one-half d. all of the night sky
Wave Characteristics: At a certain instant in time, the electric field of an electromagnetic wave in free space points in the -z direction, and the magnetic field points in the +y direction. In what direction is this wave traveling?
A. +x direction B. -x direction C. +y direction D. -z direction E. +z direction
The type of EM radiation that has wavelength just a bit longer than that of visible light is
a. ultraviolet. b. infrared. c. x-ray. d. microwave. e. gamma ray.