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Electrical Engineering Objective Questions { Electromagnetism }

134.  According to Lenz's law, the direction of induced emf and hence current
A. may be found by the right-hand rule
B. is always determined by the rate of cutting flux
C. always opposes the cause producing it
D. depends on whether the coil is wound with a right or left-hand spiral.
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135.  When electromagnetic waves are reflected at an angle from a wall, their wavelength along the wall is
A. the same as in free space
B. the same as the wavelength prependicular to the wall
C. shortened because the Doppler effect
D. greater than in the actual direction of progapation.
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136.  Transmission of power to a load over a transmission line achieves optimum value when standing-wave ratio (SWR) becomes
A. 2 :
B. 1 : 2
C. 1 : 1
D. 1 :
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137. The relationship between SWR and of a transmission line isKr + 1
A. SWR =1 - K1 + Kr
B. SWR =K - 1Kr1 + K
C. SWR= 1 - K r
D. SWR=r1 - K
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138.  The characteristic impedance of a lossless transmission line is given by
A. ./1E
B. ,/i7c-
C. 1/1E-c?
D. ,/E71,
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139.  The average noise temperature of earth, as viewed from space, is
A. 254?K
C. 100?K
D. 500?K
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140.  A plane electromoagnetic wave in free space is spacified by the electric field ax 120 cos (cot ?13z) +5 cos (cot +13z) V/m.
A. --I---- [20 cos (cot ? 13z) + 5cos (tot + Pz) 20n
B. -j-j--I20n [20cos (tot ? I3z) + 5cos (tot + I3z)
C. [20cos (cot ? I3z) + 5t cos (tot +I3z) 1 207(a x)
D. ?I 207t [20cos(wt ? I3z) + 5t cos (tot + 13z)
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