In impulse turbine operation, energy transfer to the blades is primarily achieved by which phenomenon?

• A. Reduction of steam flow in the nozzles
• B. Increase in steam velocity after passing through the blades
• C. Decrease in steam pressure across the rotating blades
• D. Increase in steam temperature

Answer: (B)

The main idea is that energy is transferred to the blades by impulse—through changing the momentum of a high-velocity steam jet. In an impulse turbine, stationary nozzles accelerate the steam, converting enthalpy into kinetic energy. The moving blades then deflect this jet, imparting a tangential impulse to the rotor. Because the blades are turning, the steam leaves with a greater tangential velocity component relative to the rotor, which corresponds to transferring kinetic energy from the steam to the blade. The pressure drop happens largely in the nozzle, not across the moving blades, and temperature rise isn’t the primary mechanism.