Solution for Question 1 : IES Conventional 1997 : Electronics & Telecommunication Engineering : Paper I

Q.1. (b): A Germanium diode has reverse saturation current of 30 uA at 125°C. What are its dynamic forward and reverse resistances for a bias 0.2 V at this temperature ?  

Solution: The dynamic resistance of diode is given by - 

Now, for Germanium diode, n = 1
at 125°C = (125 + 273) K = 398 K,   VT = 398 / 11600 = 34.3 mV 

For forward resistance, we need to use V = 0.2 V,

Similarly, for reverse resistance, use V = -0.2 V,

Q.1. (c): The Fourier transforms of the input and output of a linear time invariant system are   and  respectively. 

What is its impulse response? 

Solution: Actually, it is very easy to understand the system functions in Laplace transformation rather than Fourier Transformation. Here, we are going to change the Fourier Transformation into Laplace transform function by replacing "jw" to "s". 

We know, 

impulse response = output of the system / Input of the system

now, put jw = s,

hence, substituting s = jw,  

This is an required impulse response for given transfer function.

Q.1. (e): The electric field intensity in air is given by:  

   E = sin θ. cos (6e+7t - 0.2r) aφ V/m

Determine β and H.

Solution: In the given equation of electric field intensity, by comparing we can conclude the value for "W" and will be able to determine the value of β

We know that,

W = 2πf = 2πC/ λ =  βC 

=>  β = W/C = (6e+7)/(3e+8) = 0.2

We also know the relation between electric field intensity and magnetic field intensity as - 

E = ηH 

=> H = E/η = (sin θ / 120πr). cos (6e+7t - 0.2r) aφ I/m

This is an required expression for magnetic field intensity.