What two main factors determine whether the rotor is moved by a direct impulse or reaction?

The reason the angle at which the steam hits the moving blades is the correct answer lies in the fundamentals of how turbines operate, particularly in distinguishing between direct impulse and reaction types.

In a direct impulse turbine, steam is directed onto blades at a specific angle, resulting in a sudden change of momentum that propels the rotor. This design relies on the steam's kinetic energy, imparting a direct force on the blades as the steam expands and exits the blade system. The angle at which the steam impacts is crucial because it determines the effectiveness of this momentum transfer, affecting the rotor's ability to convert steam energy into mechanical energy.

In contrast, a reaction turbine uses the pressure differential created in the blades to produce motion. The angle facilitates not just the initial impact but also how the steam interacts as it passes through the turbine blades, creating both an impulse and a reaction effect.

The other factors listed, such as weight and size of the rotor, steam pressure, and temperature of the steam, certainly play roles in overall turbine performance and efficiency. However, they do not directly dictate whether the rotor motion is chiefly due to impulse or reaction, which is fundamentally reliant on the interaction angle of the steam with the turbine blades. This understanding clarifies the distinction between