It is not possible to determine how many revolutions a centrifuge has completed after it has been turned off without additional information. The number of revolutions a centrifuge completes will depend on a variety of factors, including the speed at which it is spinning, the length of time it has been running, and the characteristics of the sample being separated. To determine the number of revolutions a centrifuge has completed, you would need to know the speed at which the centrifuge was spinning, the length of time it was running, and the size and shape of the rotor. You would also need to know the specific type of centrifuge and its characteristics, as different models may have different rotor sizes and shapes, and may spin at different speeds. Without this information, it is not possible to determine the number of revolutions a centrifuge has completed after it has been turned off.