#### Electrical engineering

• ( 1 ) A machine without commutator, providing an ac emf to the external circuit is called as

• 1) D.C. generator
• 2) Alternator
• 3) Synchronous motor
• 4) Transformer
• Discussion in forum
Solution : A machine without commutator, providing an ac emf to the external circuit is called as Alternator

discussion

• ( 2 ) Permanent magnet d.c. motors are extensively used in

• 1) Automobiles
• 2) Heaters
• 3) Air conditioners
• 4) All of these
• Discussion in forum
Answer : 4) All of these
Solution : PMDC motor is extensively used where small dc motors are required and also very effective control is not required, such as in automobiles starter, toys, wipers, washers, hot blowers, air conditioners, computer disc drives and in many more.

discussion

Answer : 4) All of these

• ( 3 ) Linear induction motor is used in which purpose?

• 1) Traction.
• 2) Magnetic attraction.
• 3) Mechanical workshop.
• 4) Textile mills.
• Discussion in forum
Solution : Linear induction motor is used in Traction.

discussion

• ( 4 ) Swinburne's test and brake tests

• 1) Both are direct method of testing
• 2) Direct method of testing, indirect method of testing
• 3) Indirect method of testing, direct method of testing
• 4) Both are indirect method of testing
• Discussion in forum
Answer : 3) Indirect method of testing, direct method of testing
Solution : Swinburne's test is an indirect method of testing a dc machine. It is named after Sir James Swinburne. Swinburne's test is the most commonly used and simplest method of testing of shunt and compound wound dc machines which have constant flux. In this test the efficiency of the machine at any load is pre-determined.

discussion

Answer : 3) Indirect method of testing, direct method of testing

• ( 5 ) The speed in d.c. machine can be measured by using

• 1) Anemometer
• 2) Tachometer
• 3) Voltmeter
• 4) Ammeter
• Discussion in forum
Solution : The speed in d.c. machine can be measured by using tachometer

discussion

• ( 6 ) The rotational losses in d.c. machines is equal to the

• 1) Kinetic energy of armature
• 2) Half of the kinetic energy of armature
• 3) Square of the kinetic energy of armature
• 4) Rate of change of kinetic energy
• Discussion in forum
Answer : 4) Rate of change of kinetic energy
Solution : The rotational losses in d.c. machines is equal to the rate of change of kinetic energy

discussion

Answer : 4) Rate of change of kinetic energy

• ( 7 ) Brushes in d.c. machines are made up of

• 1) Cast iron
• 2) Mild steel
• 3) Copper
• 4) Carbon
• Discussion in forum
Solution : Carbon has a very high melting point (~3500°C) compared with other conductors.

discussion

• ( 8 ) In a d.c. machine, the eddy current losses mainly occurs in

• 1) Armature
• 2) Windings
• 3) Yoke
• 4) At brush contact
• Discussion in forum
Solution : As iron core of the armature is rotating in magnetic field, some losses occurred in the core which is called core losses. Normally, machines are operated with constant speed, so these losses are almost constant. These losses are categorized in two form; Hysteresis loss and Eddy current loss

discussion

• ( 9 ) If in the d.c machine, the reversal of current in the coil is faster than ideal or linear commutation then the commutation is said to be

• 1) Retarded commutation
• 2) Under commutation
• 3) Accelerated commutation
• 4) Ideal commutation
• Discussion in forum
Solution : If in the d.c machine, the reversal of current in the coil is faster than ideal or linear commutation then the commutation is said to be Accelerated commutation

discussion

• ( 10 ) In electric traction, which type of motor is generally used?

• 1) Shunt motor
• 2) Series motor
• 3) Cumulative compound motor
• 4) Differential compound motor
• Discussion in forum