Q. No. 1 – 25 Carry One Mark Each 1. Consider the following statements regarding the complex Poynting vector P for the power radiated by a point source in an infinite homogeneous and lossless medium. Re P denotes the real part of P . S denotes a spherical surface whose

()

ɵ centre is at the point source, and n denotes the unit surface normal on S. Which of the following statements is TRUE?

() (B) Re (P ) increases with increasing radial distance from the source (C) ∫∫ Re (P ) .n dS remains constant at any radial distance from the source

(A) Re P remains constant at any radial distance from the source s (D)

∫∫ Re (P ) .n dS s decreases with increasing radial distance form the source

Answer: - (D) Exp: -

∫∫

S

ˆ Re P .nds gives average power and it decreases with increasing radial

()

distance from the source 2. A transmission line of characteristic impedance 50Ω is terminated by a 50Ω load. When excited by a sinusoidal voltage source at 10GHz, the phase difference π radians. The between two points spaced 2mm apart on the line is found to be 4 phase velocity of the wave along the line is

(A) 0.8 × 108 m / s Answer: - (C) Exp: - Z0 = 50Ω ; ZL = 50Ω For

(B) 1.2 × 108 m / s

(C) 1.6 × 108 m / s

(D) 3 × 108 m / s

π radians the distance is 2mm 4 ω 2 × π × 1010 = = 16 × 10−7 = 1.6 × 108 m / s 2π β 16 × 10−3

The phase velocity vP =

3.

An analog signal is band-limited to 4kHz, sampled at the Nyquist rate and the samples are quantized into 4 levels. The quantized levels are assumed to be independent and equally probable. If we transmit two quantized samples per second, the information rate is ________ bits / second. (A) 1 (B) 2 (C) 3 (D) 4

Answer: - (D) Exp: - Since two samples are transmitted and each sample has 2 bits of information, then the information rate is 4 bits/sec.

EC-Paper Code-B

GATE 2011

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