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MCQ
861. The direction of rotation of DC series motor can be changed by-
Interchanging field terminal
Interchanging supply terminal
Both a & b
None of the above
864. Why is the speed of DC shunt motor dependent on Back EMF?
Because flux is proportional to the armature current
Because armature drop is negligible
Because Back EMF is equal to armature current
Because flux is constant in DC shunt motor
865. What will happen when the DC motor is connected to A.C supply?
DC motor will run at rated speed
DC motor will burn
DC motor will run at slow speed
Both b & c
866. In the DC machine, the fractional pitch winding is used-
To reduce the harmonic in generated EMF
Improve cooling
Increase EMF
To reduce the copper losses
868. The basic electrical requirement is art. Welding is that there should be-
coated electrodes
high open-circuit voltage
no arc blow
de power supply
871. The ratio of starting torque to full load torque is least in-
Differential compound motor
Shunt motor
Series motor
Cumulative compound motor
872. If the back EMF of DC motor vanishes then-
The motor continues to run
Motor will stop
Armature will burn
The motor continues to run in slow speed
875. When the speed of DC motor is increased-
Back E.M.F increases and current drawn decreases
Back E.M.F decreases and current drawn increases
Back E.M.F and current drawn both increases
Back E.M.F and current drawn both decreases
877. Counter EMF of the DC motor is-
Less than the applied voltage
More than the applied voltage
Equal to the applied voltage
None of the above
878. Which DC motor has the least percentage increase in input current for the same percentage increase in torque?
Separately excited motor
Series motor
Shunt motor
Compound motor