127.  The maximum usable frequency of an ionospheric layer at 60? incidence and with 8 MHz critical frequency is
A. 16 MHz
B. 1 6 / NG MHz
C. 8 MHz
D. about 6.93 MHz

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128.  The velocity of a travelling electromagnetic wave in free spece is given by 2.4a z
A. Ao Eo
B. It 96
C.1
D.Eo

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129. Consider the following statements regarding Maxwell's equations in differential form (symbols have the usual meanings)1. For free space V x H = (a+ jw E 2. For free space V . D = p 3. For steady current VxH=J 4. For static electric field V D = p Of these statements :
A. 1 and 2 are correct
B. 2 and 3 are correct
C. 3 and 4 are correct
D. 1 and 4 are correct

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130.  The expression for B, given that in free Space E = 15 cos (67t x 108 t - 2itz) ix V/m is
A. 5 x 10-8cos (6n x 108t -2nz)iy
B. -90n x 108 sin (6n x 108t -2nz)ix
C.-45 x 108 sin (6n x 108t -2nz)iy
D. 5 x 10-81-cos (6n x1 08t - 2nz)- sin(6n x 108t-2nz)iz]

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131. An air filled rectangular waveguide has dimensions 6cm x 4cm. The cut off frequency for TEio is
A. 2.5 GHz
B. 25 GHz
C. 25 MHz
D. 5 GHz

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132.  Sparking occurs when a load is switched off because the circuit has high
A. inductance
B. capacitance
C. resistance
D. none of the above

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133.  When an iron core is placed between the poles of a permanent megnet as shown in figure below, the magnetic field pattern is
A.
B.
C.
D.

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