Using the above circuit and plots a Referring to the first p

Using the above circuit and plots:

a) (Referring to the first plot) What is the amplitude of the voltage at the 3dB frequency of the gain (159 kHZ). Why is it this value and not 0.5V.

b) Referring to the second set of plots, what is the phase at DC?

c) Referring to the second set of plots, What happens to the curves if the inductance is increased by a factor of 10?

Solution

a) if observe above figure inductor and resistor are in series. same current is flowing through R,L. so if u consider this current as a reference the inductor, resistor voltage voltage phasors will be 90 degrees to each other. we need to consider the vector sum insted of algebric sum. so when we consider same voltage drops across L and R. the input voltage will be 1.414 (root 2 ) times of voltge across R or L so 1.141 times of input considered as cutoff frequncy. after this vr will become very less compared with vl. (gain 1.414 = 20 log(1.141)db = 3db).

b) from the phase plot we can say 0 deg phase diffence at low frequncy.(actully the frequncy responce plot give information about stady state output for sinusoidal signal. but in case of DC signal Thare is no concept of phase )

c) thats depends on the cut of frequncy of filter placed parllel to the inductor. if the cut of frequncy of the pallel filter is less than R/(2pi*L) with L= 1mh then cut off frequncy of the circuit will reduce. if it is higher then thare will be no change