A) 1 b) 0 c) from 0 to 1 d) more than 1 e) may be any value

Answer: B

127. For RL circuit when frequency increases 2 times the impedance of the circuit _______.

A)increases 2 times

B) decreases 2 time

C) increases less than 2 times

D) decreases more than 2 times

E) decreases less than 2 times

Solution: Z₁=R²+(L)², Z₂=R²+(2L)², so if R=2Ω, L=2Ω, 2L=4Ω, Z₁=2²+2²=8 Ω

Z₂=2²+4²=20 Ω. Z₂/Z₁=20/8=1.58

Answer: C

128. If a waveform has a half-wave symmetry the Fourier series consist of _______ harmonics.

A) sine

B) cosine

C) sine and cosine odd

D) sine and cosine even

E) sine odd and cosine even

Answer: C

129. Choose the expression, which corresponds to position of the vector (fig.17).

Fig.17 fig.18

A) A - jB

B) –A + jB

C) A+ jB

D) –A - jB

E) –A ± jB

Answer: B

130. Choose the correct sequence of elements (they are connected in series), which corresponds to the vector diagram in fig.18.

A).L, R, L, R

B)C, R, L, R

C). R, L, R, C

D). C, R, L, C

E) R,L,C,L

Answer: B

131. The circuit, which corresponds to vector diagram in fig.18 has ________ character, because current ________ resultant voltage.

A)Resistive-inductive, lags

B) Resistive-capacitive, lags

C) Resistive-capacitive, leads

D) Resistive-inductive, lead

E) Resistive-capacitive, in phase

Answer: A

132.An exponential waveform has v(0)=5V and v(2)=1.25V. What are values of v(t) at t=1s and t=4s?

A) 4V, 0.13V

B) 3V, 0.325V

C).2.5V, 0.3125V

D) 1V, 0.285V

E) 1,5V, 0.785V

Solution:

V(0)=5V; V(2)=1.25V ; V(1)=? ;V(4)=?

v(t)=[v_Ae^-t/Tc_{] U(t)}

v(0)= v_A=5V;

v(2)=5e^{-2/ Tc} =1.25V;

e^{-2/ Tc} =0.25;

T_C=1.44269;

v(1)=5e^-0.693=2.5V; v(4)=5e^-2.773=0.3125V ;

Answer: C

133. When inductor impedance for the third harmonic equals to j300 Ω its impedance for the sixth harmonic equals to ___ Ω.

A) -j600

B) j1000

C) j1200

D) j600

E) j200

Solution:

Z_3L=3jL;

Z_6L=6jL;

jL = Z_3L/3;

Z_6L=6 Z_3L/3=j600

Answer: D

134. One ray of star consists of 2-F capacitor, the second ray of the star is series combination of 2-Ω resistor and 1-F capacitor, and the third ray of the star is the series combination of 1-Ω resistor and 1-H inductance. Define the star’s rays impedances in S-domain.

A) 1+s, 2+1/s, 1/2s

B) 1+2s, 1/s, 2/s

C) 1+s, 2/s,2

D) 1+s, 2/s, 2+1/s

E) 1+2s, 2/s, 1+s

Solution:

First ray: Z₁ = 1/2s;

Second ray: Z₂ = 2+1/s;

Third ray: Z₃= 1+s;

Answer: A

135. When for RLC series circuit X_L=X_C the circuit works like

A) short circuit

B) open circuit

C) it doesn’t work

D) its impedance is equal to 0

E) its impedance is equal to resistance

Answer: E

136. If a waveform has even symmetry the Fourier series consist of _______components

A) sine

B) cosine

C) sine and cosine odd

D) sine and cosine even

E) Dc component and cosine components

Answer: E

137. An exponential waveform has v(0)=1.2V and v(3)=0.5V. What are amplitude and time constant for the waveform?

A) 1.2V, 5.13s

B) 3V, 5.13s

C) 1.2V, 3.43s

D) 1.2V, 4.28s

E) 2,5V, 4.28s

Solution:

v(t)=[v_Ae^-t/Tc_{] U(t)}

v(0)= v_A=1.2V

v(3)= 1.2e^{-3/ Tc} =0.5V;

e^{-3/ Tc} =0.42;

-3/ T_C= - 0.875

T_C=3.43s

Answer: C

138. What statement is correct?