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Electrical Engineering Objective Questions { Basic Concept of Electricity }

106. When two coils having self inductances of L1 and L2 are coupled through a Q mutual inductance M, the coefficient of coupling, K is given by Fig. 1.13
A. K = 41-2L1L2
B. K = IFF2
C. K =2M
D. K = r-

107. The overall inductance of two coils connected in series, with mutual inductance aiding self inductance is L1 with mutual inductance opposing self-inductance the overall inductance is L2. The mutual inductance M is given by
A. Li + L2
B. LI? L2
C. ? (L, ? L,)
D. ?1 (L, + L,)

108. The coils having self inductance of 10 mH and 15 mH and effective inductance of 40 mH, when connected in series aiding. What will be the equivalent inductance if we connect them in series opposing?
A. 20 mH
B. 10 mH
C. 5 mH
D. zero

109. The coupling between two magnetically coupled coils is said to be ideal if the coefficient of coupling is
A. zero

110. Two inductive coils with self inductance L1 and L2 are magnetically coupled in series opposing and in parallel aiding respectively. The mutual inductances between the coils in the two cases are respectively.L1 L2 ? M2
A. Li + L2 + 2M,
B.Li + L2 ? 2M
C.(b) + L2 ? 2M, Li + L2 + 2m
D.(c) Li + L2 ? 2M, I + L2 ? 2M

111. Two coupled coils with L1 = L2 = 0,611 have a coupling coefficient of k = 0.8.NI The turn ratio ? is N2

112. Magnetic staturation of iron means
A. the state when changes in magnetics field strength H causes a little change in the magnetic flux density B.
B. the state when a little change in magnetic field strength H causes a larger change in the magnetic flux density.
C. magnetization of iron to the maximum extent.
D. none of the above.

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