Answer: B. 92. What is time constant for the circuit in Fig.10?

 

92. What is time constant for the circuit in Fig.10?

A. 3L/5R B. L/3R C. 2L/3R D. 3R/2L E. 2L/5R Fig. 10

Solution:

T_C=G_NL

;

Answer: A.

 

 

93. What is time constant for the circuit whose solution is i_L(t)=30e^-200t-20 mA t≥0.

A. 10 ms B. 20 ms C.1ms D. 5 ms E. 30 ms

 

Solution:

i_L(t)=[i_L(0) – i_L(∞)]e^-t/Tc+ i_L(∞);

-t/T_C= -200t

1/T_C=200

T_C=1/200=0.005=5 ms

Answer: D.

 

 

94. What is differential equation whose solution is v_C(t)= - 20e^-1000t+20 V t≥0.

A. (dv_C/dt)+100v_C= -10u(t) B. (dv_C/dt)+1000v_C= -10u(t)

C. (dv_C/dt)+100v_C= 10u(t) D. (dv_C/dt)+1000v_C= 10u(t)

E. (dv_C/dt)+1000v_C= 20000u(t)

 

Solution:

v_C(t)= - 20e^-1000t+20 V

RC-circuit with step-response.

General equation is

with general solution of the form

v_C(t)=[v_C(0) – v_C(∞)]e^-t/Tc + v_C(∞)

v_A=v_C(∞)=20V

T_C=R_TC=1/1000; Thus we have

Multiplying by 1000 gives

Answer: E.

 

 

95. When we transform the circuit from time domain into S-domain the capacitor must be represented as

A. capacitor admittance and current source, which is connected with the capacitor in parallel

B. capacitor impedance and current source, which is connected with the capacitor in series

C. capacitor impedance and voltage source, which is connected with the capacitor in series

D. capacitor impedance and voltage source, which is connected with the capacitor in parallel

E. A and C are both correct

 

Solution:

1) Capacitor impedance and voltage source, which is connected with the capacitor in series;

2) Capacitor admittance and current source, which is connected with the capacitor in parallel.