A. φ = cos-1V/VR
B. φ = cos-1V × VR
C. φ = cos-1VR/V
D. φ = tan-1V/VR
Answer: C
From the voltage triangle, we get
cosφ = VR/V.
Hence φ = cos-1VR/V.
22 What is sinϕ from the impedance triangle?
A. XL/R
B. XL/Z
C. R/Z
D. Z/R
Answer: B
In the Impedance triangle, the Base is R, Hypotenuse is Z, and Height is XL.
So, sinϕ = XL/Z.
23. What is the resonance frequency of ac circuit?
A. 1/√LC
B. √(L/C.
C. √LC
D. LC
Answer: A
At resonance, XL = XC
ωL = 1/ωC
ω = 1/√LC.
24. What is impedance at resonance?
A. maximum
B. minimum
C. zero
D. cannot be determined
Answer: B
At resonance, XL = XC
Z2 = R2+(XL-XC)2
Z = R So Z is minimum at resonance.
25. What is the value of impedance at resonance?
A. XL
B. XC
C. R
D. 0
Answer: C
At resonance, XL = XC
Z2 = R2+(XL-XC)2
Z = R So Z is minimum at resonance.
26. What is φ in terms of voltage?
A. φ = cos-1V/VR
B. φ = cos-1V × VR
C. φ = cos-1VR/V
D. φ = tan-1V/VR
Answer: C
From the voltage triangle, we get
cosφ = VR/V.
Hence φ = cos-1VR/V.
27. What is tanϕ for the RC circuit?
A. XC/R
B. XL/R
C. R/Z
D. Z/R
Answer: A
From the impedance triangle, height gives capacitive reactance, and base gives resistance.
tanϕ = XC/R.
28. What is the resonance condition?
A. When XL>XC
B. When XL<xC C. When XL = XC
D. When XC = infinity
Answer: C
The current is in phase with the voltage when the capacitive reactance is in equal to the inductive reactance. This is known as the resonance condition.
29. What is the frequency in the resonance condition?
A. Minimum
B. Maximum
C. Cannot be determined
D. Zero
Answer: B
At the resonance condition, the frequency is maximum since the inductive reactance is equal to the capacitive reactance. XL = XC.
30. Can the capacitor fully charge using alternating current?
A. yes
B. no
C. may or may not
D. depend on the value of capacitance
Answer: A
No, the capacitor cannot be fully charged using alternating current because as soon as the capacitor charges, the alternating current reverses its polarity thereby discharging it.
