# Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-12

166. Which of the following expression is correct for series reactance Xcs if three capacitors C1, C2 and C3 are connected in series?

a) 1/Xcs = 1/Xc1 + 1/Xc2 + 1/Xc3
b) Xcs = Xc1 + Xc2 + Xc3
c) Xcs = 1/Xc1 + 1/Xc2 + 1/Xc3
d) Xcs = 1/Xc1 + Xc2+ Xc3

Ans: (b)

167. An RC network is shown blow, can be used as high pass and low pass filter as well. For which of the condition lower cut-off frequency occurs as high pass filter ?

a) ES = ER
b) ES+ EC
c) ER=0.707 EC
d) ER= 0.707 ES

Ans: (d)

168. Which of the following relationship shown by curves is true for inductive circuit ?

169. The Laplace transform of the unit function is given by

a) 1/s
b) 1/s2
c) S
d) 1

Ans: (a)

170. The Laplace transform of the function ƒ(t) = E-at is given by

a) 1/a2+ s2
b) 1/a+s
c) 1/a+s
d) s2/a2+ s2

Ans: (b)

171. The Laplace transform of the function ƒ(t) = cos⁡βt is given by

a) β/s22
b) s/s22
c) 1/22
d) β/s+β

Ans: (b)

172. The Laplace transform of the function ƒ(t) = sin⁡βt is given by

a) β/s+β2
b) β/s22
c) s/s22
d) β2/s+β

Ans: (a)

173. Whish of the following is the Laplace transform of ƒ(t) = t ?

a) 1/s
b) 1/s2
c) 1/s3
d) S

Ans: (a)

174. The expression £ (t) = n1/sn+1 is true the function

a) ƒ(t) = tn
b) ƒ(t) = ntn
c) ƒ(t) = t/n
d) ƒ(t) = tn

Ans: (a)

175. Which of the following conditions are necessary for validity of “Initial Value Theorem”

Line s F(s) = line ƒ(t)

s →∞ t → 0

a) ƒ(t) and its derivative ƒ(t) must have Laplace transformer
b) if the Laplace transform of ƒ(t) is F(s), the lim sF(s) must exist
c) only ƒ(t) must have Laplace transformer
d) (a) and (b) both

Ans: (d)

176. The Laplace transform of a unit impulse at t = 0 is

a) S
b) 1/s
c) Unity
d) 1/s2

Ans: (c)

177.If the Laplace transform of unit step is 1/s. How many poles will be located at the origin of the s-plane?

a) One
b) Two
c) Three
d) None

Ans: (a)

178. If the Laplace transform of the function ƒ(t) = e-at is 1/(s+α) then Which of the following statement will be true?

a) One pole will be located on the real axis of s-plane at – α
b) One pole will be located on the imaginary axis of s-plane at ± ϳω
c) One complex pole will be located at the origin of s-plane
d) One complex pole will be located in s-plane at – α ± јω

Ans: (a)

179. For which of the following function the Laplace will be 2/s2

a) ƒ(t) = t
b) ƒ(t) = 1
c) ƒ(t) = δt
d) ƒ(t) = 2t
e) ƒ(t) = t2

Ans: (e)

180. Which of the following operations is to be carried on to get ramp function from unit impulse at t = 0 ?

a) integrate unit impulse function once
b) integrate unit impulse function twice
c) integrate unit impulse function thrice
d) differentiate unit impulse function twice
e) differentiate unit impulse once as a function of time

Ans: (c)