Question 1

Most DC speed controllers use solid-state devices such as ___________to provide speed control for the motor.

Accepted Answer

Solid-state devices such as Silicon Controlled Rectifiers (SCRs) are commonly used in DC speed controllers to provide speed control for the motor. Most DC speed controllers use Solid State Devices like SCRs to control the motor speed.

Question 2

Normal or base speed for a DC motor is obtained by connecting full voltage to both the armature and shunt field.

Accepted Answer

When full voltage is applied to both the armature and shunt field, the DC motor runs at its normal or base speed. Connecting full voltage to both the armature and shunt field provides normal or base speed for a DC motor.

Question 3

The direction of armature rotation of a DC motor depends on the direction of the current in the field and armature circuits.

Accepted Answer

The direction of armature rotation of a DC motor is determined by the right-hand rule, which states that the direction of rotation is perpendicular to the direction of the magnetic field and the direction of the current in the armature circuit. Therefore, the direction of armature rotation does depend on the direction of the current in the field and armature circuits. The direction of armature rotation is determined by the interaction between the magnetic field of the armature and the magnetic field created by the current in the field circuit. The direction of current flow in both the field and armature circuits determines the direction of their respective magnetic fields, thus determining the direction of armature rotation.

Question 4

Three types of DC industrial motors are widely used: series, shunt, and_____________ .

Accepted Answer

Series and shunt motors have limitations in terms of their speed regulation and torque characteristics. Compound motors, on the other hand, combine the features of both series and shunt motors, resulting in better speed regulation and high starting torque. Therefore, compound motors are the best choice for various industrial applications. The three common types of DC industrial motors are series, shunt, and compound. Therefore, the missing option is compound.

Question 5

The armature current must be limited by an external resistor or a_____________ rheostat.

Accepted Answer

The armature current must be limited by a starting rheostat during the starting of the motor. Once the motor reaches its full speed, the starting rheostat is bypassed. A liquid rheostat is not a common option for limiting armature current, and a constant or disc rheostat is not suitable for the purpose. The most common method to limit the armature current in a DC motor is by using a starting rheostat, also known as a rotor resistance starter. This device limits the armature current at start-up to prevent the motor from being damaged due to excessive current. A constant resistor or disc rheostat are not ideal choices as they do not provide variable resistance to adjust the armature current. Liquid rheostats are not commonly used and are more expensive than other options.

Question 6

The essential features and parts of DC motors and generators are the same.

Accepted Answer

Both DC motors and generators have similar components including a stator, rotor, commutator, and brushes. The main difference is that in a motor electrical energy is converted to mechanical energy, while in a generator mechanical energy is converted to electrical energy. DC motors and generators share common features and parts such as a rotor, stator, and brushes. They both operate based on the principles of magnetic fields and electromagnetic induction. However, their functions and practical applications differ.

Question 7

The direction of rotation of a DC motor is determined by facing the commutator end of the motor, which is generally the __________of the motor.

Accepted Answer

The commutator end of a DC motor is generally located at the rear of the motor, so facing this end determines the direction of rotation.

Question 8

By controlling the ohms supplied to the motor windings, a wide range of motor speeds can be obtained.

Accepted Answer

Motor speed is primarily controlled by adjusting the voltage or frequency supplied to the motor, not by controlling the ohms (resistance) in the motor windings.

Question 9

The armature or rotating member of a DC motor is a cylindrical ________assembly mounted directly on the motor shaft.

Accepted Answer

The armature of a DC motor is typically made of iron because it is a good conductor of electricity and can create a strong magnetic field when a current flows through it. Carbon, graphite, and steel are not commonly used materials for the armature. The armature or rotating member of a DC motor is typically made of stacks of thin laminations of high-quality magnetic iron, which helps to reduce energy losses due to hysteresis and eddy currents. Carbon, graphite, and steel are not typically used for the armature of a DC motor.

Question 10

Three factors limit the current taken by the armature from a DC source.

Accepted Answer

The answer of Three factors limit the current taken by...

Quiz 43: About Dc Motors