A25-cm-long, center-fed, wire-type antenna is made of copper wire (nonmagnetic, σcu = 5.8×107 s/m) with a radius of 1 mm. the antenna is excited by a sinusoidal current with an amplitude i0 = 5 a. determine the antenna gain (in db) and the time average power radiated, if the frequency is

(a) 1 mhz,
(b) 0.6 ghz.
(c) at what operating frequency the given antenna is more efficient and what is the ratio (in db) of powers emitted at 0.6 ghz and 1 mhz?

Line joining liquid phase with liquid and solid phase mixture is known as: a) liquidus b) solidus c) tie line d) none of the mentioned

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?

How much power could a wind turbine produce if it had the following specifications? cp = 0.45 -d=1.2kg/m3 d=50m v 5m/s