Hi friends, this is post about objectives of electrical engineering with emphasis on dc motor check out and comment...
1) The speed of a dc motor is
A) directly proportional to back emf and flux
B) directly proportional to its back emf and inversely proportional to flux
C) inversely proportional to back emf and flux
D) directly proportional to flux and inversely proportional to back emf
Ans:B
2) The speed of a dc shunt .............. from no load to full load
A) falls sightly
B) improves slightly
C) remains unchanged
D) falls rapidly
Ans:A
3) If the load current and flux of a dc motor are held constant and voltage applied across it armature is increased by 5%, the speed of the motor will
A) increase by 5%
B) reduce by 5%
C) remain unaltered
D) depends on other factors
Ans:A
4) A dc shunt motor runs at rated speed. If its field circuit gets open circuited, then soon after this the motor speed would tend to
A) decrease
B) remain unchanged
C) increase
D) fluctuate around its previous speed
Ans:C
5) A flywheel is normally fitted to
A) dc series motor driving a constant torque load
B) separately excited dc motor driving pulsed torque load
C) cumulatively compound motor driving torque load
D) differentially compound motor driving pulsed torque load
Ans:C
6) In an electric motor , the electromagnetic torque developed is
A) in opposite direction to both load torque and frictional torque
B) in the same direction as the load torque but in opposite direction to frictional torque
C) in the same direction as the load torque and frictional torque
D) in the same direction as the frictional torque but in opposite direction to load torque
Ans:A
7) A dc motor develops the maximum mechanical power when the armature current is such that
A) the back emf is equal to 3/4th of the applied emf
B) the back emf is equal to one-half of the applied emf
C) the back emf is equal to 1/4th of the applied emf
D) the back emf is equal to 2/3th of the applied emf
Ans:B
8) A dc shunt motor having unsaturated magnetic circuit runs at 1000 rpm with rated voltage. If the applied voltage is half of rated voltage, the motor will run at
A) 2000 rpm
B) 1000 rpm
C) 750 rpm
D) 500 rpm
Ans:B
9) An electric motor with "constant output power" will have a torque-speed characteristic in the form of a
A) straight line through the origin
B) straight-line parallel to speed axis
C) circle about the origin
D) rectangular hyperbola
Ans:D
10) T and P are the developed electromagnetic torque and the shaft power of a dc series motor. If losses are neglected, then for constant terminal voltage
A) T ∝ P
B) T ∝ 1/P
C) T ∝ √P
D) T ∝ P^2
Ans:D
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