Altarnating Current
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If instantaneous current is given by i = 4cos (ωt + ф)A, then the r, m, s value of current is
A. 4A
B. 2√2A
C. 4√2A
D. Zero A
Answer : B
If an ac main supply is given to be 220 V. What would be the average e.m.f during a positive half cycle?
A. 198 V
B. 386 V
C. 256 V
D. None of these
Answer : A
The peak value of an Alternating current is 6A, then r, m, s value of current will be
A. 3A
B. 3√3 A
C. 3√2 A
D. 2√3 A
Answer : C
Alternating current cannot be measured by dc ammeter because:
A. Ac cannot pass through dc ammeter
B. Average value of complete cycle is zero
C. Ac is virtual
D. Ac changes its direction
Solution:
In dc ammeter, a coil is free to rotate in the magnetic field of a fixed magnet. If an
alternating current is passed through such a coil, the torque will reverse its
direction each time the current changes direction and the average value of the
torque will be zero.
Answer : B
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