In power transmission through a belt passing over a pulley, the rotation speed of the driver pulley is 1200 RPM and that of the driven pulley is 1500 RPM. The ratio of diameters of driver and driven pulleys is-

Concept:

Velocity Ratio for Belt System:

• The velocity ratio is the ratio of the speed of the driven pulley to that of the driving pulley.
• The speed is inversely proportional to the diameter of the pulley.

Velocity Ratio = \(\frac{N_{driven}}{N_{driver}} = \frac{D_{driver}}{D_{driven}}\)

where N_driven = Speed of Driven Pulley, N_driver = Speed of Driver Pulley, D_driver = Diameter of Driver Pulley, D_driven = Diameter of Driven Pulley

Calculation:

Given:

N_driver = 1200 RPM, N_driven = 1500 RPM

\(\frac{1500}{1200} = \frac{D_{driver}}{D_{driven}}\)

\(\frac{D_{driver}}{D_{driven}} = 1.25\)

The ratio of diameters of the driver and driven pulleys is 1.25.