Incorrect Pairing in Power Transmission

Positive drive .... Belt drive

High velocity ratio .... Worm gearing

To connect non-parallel and non-intersecting shafts .... Spiral gearing

Diminished noise and smooth operation .... Helical gears

Explanation:

Power transmission is an essential aspect of mechanical engineering. There are several ways to transmit power from one machine to another, and each mechanism has its unique features. The given pairs are all used in power transmission, but one of them is incorrectly paired. Let us see each pair's features and understand why one pair is incorrect.

Positive drive .... Belt drive

A belt drive is a mechanism used to transmit power from one shaft to another using a belt. Belt drives are used when high-power transmission is required. The belt is wrapped around a pulley, and the rotation of one pulley drives the belt, which, in turn, drives the other pulley.

High velocity ratio .... Worm gearing

Worm gearing is used when high velocity reduction is required. It is used to transmit power between two perpendicular shafts. Worm gearing has a high velocity ratio, which means that the output shaft rotates slower than the input shaft. It is used in heavy machinery, such as lifts and cranes.

To connect non-parallel and non-intersecting shafts .... Spiral gearing

Spiral gearing is used to transmit power between non-parallel and non-intersecting shafts. The spiral gears have teeth that are twisted at an angle, allowing them to mesh with each other even when the shafts are not aligned. Spiral gearing is used in machinery where the shafts are not parallel, such as in automobiles.

Diminished noise and smooth operation .... Helical gears

Helical gears are used when the transmission of power requires reduced noise and smooth operation. The teeth of helical gears are cut at an angle, which results in a smoother and quieter operation. Helical gears are used in machinery where noise reduction is necessary, such as in automobiles.

The incorrectly paired option is:

Positive drive .... Belt drive

A positive drive is a mechanism that uses teeth to transmit power. Positive drives are used when high power transmission is required, and there is no slippage between the shafts. A belt drive, on the other hand, uses a belt to transmit power and is not a positive drive. Hence, the option 'A' is incorrectly paired.

Conclusion:

The given pairs are all used in power transmission, but one of them is incorrectly paired. Positive drive is not a belt drive, and hence the option 'A' is the incorrect pairing.