Question 1: When the armature current is increased the speed of DC Shunt Motor ...................
- Increases
- Decreases
- remains constant
BASIC
NEC 2023
DC Shunt Motor Practice Test Questions
Free online DC shunt motor practice test. 25 basic electrical questions on constant-speed characteristics, back EMF, starters, speed control methods, and typical applications. Good for electrician exam prep.
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A DC shunt motor has its field winding connected in PARALLEL (shunt) with the armature, so the field current stays almost constant no matter how the load changes. This gives the shunt motor its main feature: nearly constant speed from no load to full load, which is why it is chosen for lathes, blowers, conveyors, and other constant-speed drives. Key idea: back EMF Eb = V − IaRa, and motor speed is roughly proportional to back EMF for a fixed field. A starter is always needed because, at standstill, there is no back EMF to limit the current.
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TimeDC Shunt Motor Practice Test Questions — Question List
Question 2: Under Normal Operation DC Shunt Motor draws a current of <em><strong>I</strong></em>. For the same constant power output if the terminal is halved, its current will be..............
- 1/4 I
- 1/2 I
- 2 I
Question 3: The speed of the DC Shunt motor can be increased by:
- Increasing the resistance in the armature current
- increasing the resistance in the field circuit
- decreasing the resistance in the field winding
Question 4: In a DC motor the direction of rotor rotation depends on .....................
- Rotor power
- Rotor voltage
- Rotor frequency
- Rotor current
Question 5: The back EMF produced in a DC Motor ...........
- opposes the applied voltage
- opposes the armature current
- aids the applied voltage
- aids the armature current
Question 6: The developed mechanical power in a DC motor is maximum when the back EMF is equal to ............ the applied voltage.
- double
- half
- one by third
Question 7: The amount back EMF of a shunt motor will increase when ....................
- load is increased
- supply voltage is increased
- field flux is strengthened
- field flux is weekend
Question 8: The speed of the shunt motor is practically constant.
- True
- False
Question 9: In shunt motor the field winding is connected in ................ with the armature winding.
- series
- parallel
Question 10: The field winding of a DC shunt motor is normally made of:
- Thick wire with few turns and low resistance
- Thin wire with many turns and high resistance
- Bare copper bars with no insulation
- The same wire size as the armature winding
Question 11: Which of the following are common methods to control the speed of a DC shunt motor?
- Field control, armature control, and armature voltage control
- Changing the number of phases only
- Changing the frequency of a DC supply
- There is no way to control shunt motor speed
Question 12: Field control (weakening the shunt field with a field rheostat) can only be used to move the motor speed:
- Above its normal (base) speed
- Below its normal (base) speed
- It cannot change the speed at all
- Only to exactly zero speed
Question 13: The Ward-Leonard system is used for DC shunt motors to provide:
- Smooth, wide-range speed control by varying the armature supply voltage
- A fixed single speed with no adjustment
- Only reversing of direction, not speed control
- Automatic braking with no speed control
Question 14: If the shunt field circuit of a running DC shunt motor suddenly opens (breaks) while the armature is still connected to supply, what is the danger?
- The motor can run away to a dangerously high speed
- The motor stops instantly with no risk
- The motor reverses direction safely
- Nothing happens because the armature is unaffected
Question 15: Why does a DC shunt motor need a starter (starting resistance) when it is first switched on?
- At standstill there is no back EMF, so current would otherwise be too high
- The motor cannot start without a starter under any condition
- Starters are only needed for AC motors
- It increases the field current to dangerous levels without one
Question 16: The "no-volt release" (NVC) coil in a DC motor starter is used to:
- Release the starter arm and disconnect the motor if supply voltage is lost
- Increase the motor speed automatically
- Reverse the motor direction on power loss
- Cool the armature winding
Question 17: To reverse the direction of rotation of a DC shunt motor, you should:
- Reverse the connections of either the armature or the field winding, but not both
- Reverse both the armature and field connections together
- Increase the field current
- It is impossible to reverse a shunt motor
Question 18: The overload release (thermal or electromagnetic) fitted in a DC motor starter protects the motor by:
- Disconnecting the motor from supply if current exceeds a safe limit for too long
- Increasing the supply voltage automatically
- Reversing the motor when it stalls
- Cutting off the field winding only
Question 19: The back EMF (Eb) of a running DC shunt motor is related to supply voltage (V), armature current (Ia), and armature resistance (Ra) by which equation?
- Eb = V + IaRa
- Eb = V − IaRa
- Eb = V × IaRa
- Eb = V / IaRa
Question 20: A DC shunt motor is connected to a 220 V supply. The armature resistance is 0.5 Ω and the armature current is 20 A. What is the back EMF?
- 200 V
- 210 V
- 220 V
- 230 V
Question 21: A DC shunt motor gives its maximum efficiency at the load point where:
- The variable losses equal the constant losses
- The variable losses are always zero
- The motor runs at no load
- The field current is zero
Question 22: For a DC shunt motor running with a fixed (constant) field flux, motor speed is roughly proportional to:
- The back EMF
- The armature resistance only
- The number of commutator segments
- The brush contact area
Question 23: Because of its nearly constant speed from no load to full load, a DC shunt motor is well suited for driving:
- Lathes, blowers, and conveyors that need steady speed
- Cranes and hoists needing very high starting torque only
- Electric trains only
- Battery charging circuits
Question 24: In a DC shunt motor, the shunt field copper loss is normally classified as a:
- Constant loss
- Variable loss that grows with mechanical load
- Stray load loss only
- It is not a real loss at all
Question 25: A DC shunt motor is well suited for applications requiring nearly constant speed under varying load.
- True
- False
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