Year 2 Electrical Semester
2
1. T/F The principle of operation of a DC motor is based on attraction and repulsion of magnetism.: True
2. T/F A motor is a machine that converts electrical energy into mechanical energy.: True
3. T/F The function of the commutator in a DC motor performs the function of a rotary switch to keep the
current flowing in the proper direction through the armature.: True
4. T/F The strength of the magnetic field of the pole pieces and the strength of the magnetic field of the
armature determine the amount of amperage developed by a DC motor.: False
5. T/F The shunt motor is known as a variable speed motor.: False
6. T/F
1. The strength of the magnetic field of the polepieces.
2. The number of turns of wire in the armature
3. The speed of the armature.
all determine the amount of CEMF produced in the armature.: True
7. T/ F A voltage induced in the armature windings that opposes the applied voltage is ECMF.: False
8. T/F The wire capacity of the armature limits the amount of current flow through the armature when
power is first applied to the motor.: False
9. T/F Armature resistance determines the speed regulation of a DC motor.: -
True
10.T/F A parallel motor should never be operated at no load.: False
11.T/F A differential compound motor connection should, in general be avoid- ed.: True
12.T/F Changing the armature leads is the most common way of changing the direction of rotation of a
compound motor.: True
13.T/F By connecting full voltage to both the armature and shunt field you can make a DC motor operate at its
base speed.: True
14.T/F By connecting full voltage to the armature and reducing the current flow through the shunt field you can
make a DC motor operate above its base speed.: True
15.T/F The field loss relay is a device is used to connect power to the armature if the shunt field current drops
, Year 2 Electrical Semester
2
below a certain level: False
16.T/F The resistance of the shunt field produces heat, which prevents the formation of moisture inside the
motor.: True
17.T/F Charlie Surman was the first person to establish a measurement for hp.: False
, Year 2 Electrical Semester
2
18.T/F One horsepower is equal to 950 W.: False. One horsepower is equal to 746 W.
19. A motor is operating a load that requires a torque of 750 lb-in. and is turning at a speed of 1575 RPM.
How much hp is the motor producing?: 18.782 HP
20. A motor is operating a load that requires a torque of 750 lb-in. and is turning at a speed of 1575 RPM.
How much hp is the motor producing? This motor
is connected to a 250 VDC line and has a current draw of 80A. What is the efficiency of this motor?: 70%
21.T/F Counter-electromotive force (CEMF) and back-EMF are names for the voltages induced into the
armature of a DC Motor.: True
22.A device that converts mechanical energy into electrical energy is called a .: Generator
23.When the field winding of a DC motor is connected in parallel with the armature, the motor is called a
DC motor.: shunt
24. A DC motor can develop
maximum torque at rpm.: 0 (zero) RPM
25.Magnetic field polarity of the armature must remain in
relation to the polarity of the pole pieces.: Constant
26.The speed regulation of a DC motor is proportional to the
of the armature.: Resistance
27.Series motors commonly have an average starting torque of around
% of full torque.: 450%
28.The most common type of compound motor is the shunt
because of superior speed regulation.: Long
29.How much horsepower is being produced by a motor turning at a speed of 1250 rpm and at a load of 250
lb-in.? 1.59 x 250 x ,000 = 4.96875
hp: 4.9 hp
30.DC motor has a source voltage of 120 volts, draws 2.5 amps. Speed is 1525 rpm at a torque of 6 lb-in. What is
the efficiency of the motor?
1.59 x 6 x 1525/ 100,000 = .14548 x 746 = 108.531W (out)
120 x 2.5 = 300 W (in),
, Year 2 Electrical Semester
2
108. = .36177: 36%
31.Choose the types of three phase motors below.: 1. squirrel cage induction
2. synchronous
3. wound rotor induction
32.T/F The principle of operation of all three-phase motors is a rotating mag- netic field.: True
33.T/F The number of stator poles per phase and the frequency of the applied voltage determines synchronous
speed.: True
34.T/F The speed of the rotating magnetic field is asynchronous speed.: False
2
1. T/F The principle of operation of a DC motor is based on attraction and repulsion of magnetism.: True
2. T/F A motor is a machine that converts electrical energy into mechanical energy.: True
3. T/F The function of the commutator in a DC motor performs the function of a rotary switch to keep the
current flowing in the proper direction through the armature.: True
4. T/F The strength of the magnetic field of the pole pieces and the strength of the magnetic field of the
armature determine the amount of amperage developed by a DC motor.: False
5. T/F The shunt motor is known as a variable speed motor.: False
6. T/F
1. The strength of the magnetic field of the polepieces.
2. The number of turns of wire in the armature
3. The speed of the armature.
all determine the amount of CEMF produced in the armature.: True
7. T/ F A voltage induced in the armature windings that opposes the applied voltage is ECMF.: False
8. T/F The wire capacity of the armature limits the amount of current flow through the armature when
power is first applied to the motor.: False
9. T/F Armature resistance determines the speed regulation of a DC motor.: -
True
10.T/F A parallel motor should never be operated at no load.: False
11.T/F A differential compound motor connection should, in general be avoid- ed.: True
12.T/F Changing the armature leads is the most common way of changing the direction of rotation of a
compound motor.: True
13.T/F By connecting full voltage to both the armature and shunt field you can make a DC motor operate at its
base speed.: True
14.T/F By connecting full voltage to the armature and reducing the current flow through the shunt field you can
make a DC motor operate above its base speed.: True
15.T/F The field loss relay is a device is used to connect power to the armature if the shunt field current drops
, Year 2 Electrical Semester
2
below a certain level: False
16.T/F The resistance of the shunt field produces heat, which prevents the formation of moisture inside the
motor.: True
17.T/F Charlie Surman was the first person to establish a measurement for hp.: False
, Year 2 Electrical Semester
2
18.T/F One horsepower is equal to 950 W.: False. One horsepower is equal to 746 W.
19. A motor is operating a load that requires a torque of 750 lb-in. and is turning at a speed of 1575 RPM.
How much hp is the motor producing?: 18.782 HP
20. A motor is operating a load that requires a torque of 750 lb-in. and is turning at a speed of 1575 RPM.
How much hp is the motor producing? This motor
is connected to a 250 VDC line and has a current draw of 80A. What is the efficiency of this motor?: 70%
21.T/F Counter-electromotive force (CEMF) and back-EMF are names for the voltages induced into the
armature of a DC Motor.: True
22.A device that converts mechanical energy into electrical energy is called a .: Generator
23.When the field winding of a DC motor is connected in parallel with the armature, the motor is called a
DC motor.: shunt
24. A DC motor can develop
maximum torque at rpm.: 0 (zero) RPM
25.Magnetic field polarity of the armature must remain in
relation to the polarity of the pole pieces.: Constant
26.The speed regulation of a DC motor is proportional to the
of the armature.: Resistance
27.Series motors commonly have an average starting torque of around
% of full torque.: 450%
28.The most common type of compound motor is the shunt
because of superior speed regulation.: Long
29.How much horsepower is being produced by a motor turning at a speed of 1250 rpm and at a load of 250
lb-in.? 1.59 x 250 x ,000 = 4.96875
hp: 4.9 hp
30.DC motor has a source voltage of 120 volts, draws 2.5 amps. Speed is 1525 rpm at a torque of 6 lb-in. What is
the efficiency of the motor?
1.59 x 6 x 1525/ 100,000 = .14548 x 746 = 108.531W (out)
120 x 2.5 = 300 W (in),
, Year 2 Electrical Semester
2
108. = .36177: 36%
31.Choose the types of three phase motors below.: 1. squirrel cage induction
2. synchronous
3. wound rotor induction
32.T/F The principle of operation of all three-phase motors is a rotating mag- netic field.: True
33.T/F The number of stator poles per phase and the frequency of the applied voltage determines synchronous
speed.: True
34.T/F The speed of the rotating magnetic field is asynchronous speed.: False
