Question 1

It has been suggested that synchronous motors are more expensive to install than squirrel cage motors if the rating exceeds 1 hp.

Accepted Answer

False

Question 2

Most electrically driven constant-speed machines operate at speeds below ____ rpm.&#10;A) 1800&#10;B) 2000&#10;C) 2200&#10;D) 2400

Accepted Answer

Most electrically driven constant-speed machines, such as induction, synchronous, and direct current motors, operate at speeds below 1800 rpm.

Question 3

Laser light has a single frequency with constant amplitude and ____.&#10;A) phase&#10;B) wavelength&#10;C) pulse&#10;D) head

Accepted Answer

B

Question 4

The most economical speed for an electrical motor is about 1800 revolutions per minute.

Accepted Answer

This is generally true for most standard electrical motors, although it can vary depending on the specific application and motor design.

Question 5

The ways in which a laser can be used for aligning systems are limited only by ____.&#10;A) the power of motors&#10;B) the laws of light&#10;C) the ingenuity of the users&#10;D) light dispersion

Accepted Answer

The options provided in the question suggest that the limitations of using a laser for aligning systems are either related to the technical aspects (such as motor power or light dispersion) or the physical laws of light. However, the correct answer is C, which highlights that the possibilities of using a laser for alignment depend on the creativity and resourcefulness of the users. This means that there are various ways to use a laser for alignment that might not have been explored yet or that can be adapted to specific needs and conditions. Therefore, the potential of laser alignment is not restricted by technical or physical barriers, but rather by the user's imagination and problem-solving skills.

Question 6

Five quantities must be known if the machinery is to be set up with the correct pulley sizes.

Accepted Answer

The number of quantities needed to set up machinery with the correct pulley sizes can vary depending on the specific requirements of the setup, such as the desired speed ratio, power transmission, and the diameters of the available pulleys. It does not strictly require five quantities.

Question 7

Laser light is directional.

Accepted Answer

Laser light is highly directional and can be focused to a narrow beam of light.

Question 8

Offset drives, such as V-belts, gears, and chain drives, can be lined up more easily than direct drives.

Accepted Answer

The answer of Offset drives, such as V-belts, gears, and...

Question 9

A vertical drive can cause problems because ____ tends to pull the belts away from the lower sheave.&#10;A) rotation&#10;B) gravity&#10;C) speed&#10;D) wind

Accepted Answer

Gravity is a force that constantly pulls objects towards the center of the earth. In the case of a vertical drive, this force can cause the belts to be pulled away from the lower sheave, leading to problems such as slipping or even coming off entirely.

Question 10

Induction motors are rarely used for operation at speeds below ____ rpm.&#10;A) 500&#10;B) 700&#10;C) 900&#10;D) 1200

Accepted Answer

Induction motors are designed to operate at synchronous speeds, which depend on the number of poles in the motor and the frequency of the power supply. The synchronous speed of a motor is given by the formula 120f/p, where f is the frequency of the power supply and p is the number of poles in the motor. For example, a four-pole motor operating on a 60 Hz power supply has a synchronous speed of 1800 rpm. Induction motors typically operate at speeds close to their synchronous speed, but not exactly at that speed due to slip. The amount of slip is dependent on the load on the motor. However, when the speed of an induction motor falls below a certain value, the torque developed by the motor decreases rapidly, making it unsuitable for most applications. This speed is typically around 500-600 rpm for most induction motors. Therefore, the best choice is A) 500 rpm.

Deck 43: Direct Drives and Pulley Drives