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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Lekhika
The lowest frequency at which the waveguide can propagate a signal is called cut off frequency. signal can propagate along a waveguide using a number of modes. However the dominant mode is one that has lowest cutoff frequency. And for rectangular wave guide, this is the TE10 mode. and cut off frequency in this mode is given by, fc= 1/ 2a \sqrt(mu * epsilon) so operation frequency should be equal to fc for dominant mode. So, option (B) is correct.