In an impulse turbine, what is the primary mechanism by which energy is extracted?

• A. Steam momentum strikes the turbine blade and rotates it
• B. Steam expands in a nozzle causing a pressure rise on blades
• C. The turbine wall collides with steam to create spin
• D. Electrical energy is extracted directly from steam

Answer: (A)

Energy transfer comes from momentum change. In an impulse turbine, steam is expanded in stationary nozzles to create a high-velocity jet. When that jet hits the moving blades, it is deflected, and the steam’s momentum is redirected. This impulse transfers a force to the blades, producing torque and turning the rotor. The nozzle does the main job of converting pressure energy into kinetic energy, while the rotor blades mainly extract energy by changing the steam’s direction and momentum.

Other ideas miss the mechanism: energy is not gained by a pressure rise on the blades, there’s no wall collision, and electricity isn’t drawn directly from steam—it's produced by a generator converting the turbine’s mechanical work.