HW week1

# HW week1 - 3 The voltage of an electromagnetic wave...

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ECE 107: Homework 1 Due Friday, April 2 1) Assume that the earth is electrified by a charge 2Q, and the moon by a charge Q. How large does Q have to be so the repulsive electric force between the earth and the moon be equal to the attractive gravitational force? The mass of the earth and the moon are 5.983 x 10 24 kg and 7.347 x 10 22 kg, respectively. What would the mass of the charge Q be and how does it compare to the earth’s mass. 2) A signal is traveling down a transmission line that is lossy. When the signal decays to 20% of the original signal you need to add a repeater to the line to boost the signal by a factor of 5 to the original signal level. A new repeater is developed that could boost the signal by a factor of 10 so you only need a repeater when the signal reached 10% of original signal. If this new repeater costs twice as much as the original repeater does it make sense to use the new repeater?

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Unformatted text preview: 3) The voltage of an electromagnetic wave traveling on a transmission line is given by ) 30 10 4 sin( 7 ) , ( 9 z t e t z v z π α − × = − a) Find the frequency, wavelength, and phase velocity of the wave. b) At z=2 m, the amplitude was measured to be 2 V. Find α . c) What is the amplitude of the wave measured at 10 m? 4) . A laser beam traveling through fog was observed to have an initial intensity of 1 ( μ W/m2). At a distance of 2 m from the laser it has an intensity of 0.2 ( μ W/m2). Given that the intensity of an electromagnetic wave is proportional to the square of its electric-field amplitude, find the attenuation constant α of fog. 5) 9) The voltage source of the circuit shown in the figure below is given by _ ) 45 10 4 cos( 24 ) ( 4 o − × = t t v Obtain an expression for i L ( t ), the current flowing through the inductor. 6) 7) 8)...
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## This note was uploaded on 04/02/2010 for the course ECE ECE 107 taught by Professor Ericfullerton during the Spring '07 term at UCSD.

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HW week1 - 3 The voltage of an electromagnetic wave...

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