Place test tubes containing approximately equal volumes in opposite positions on the rotor. wait until all positions on the rotor contain a test tube before activating the centrifuge. never put stoppers or other items in the centrifuge with your tubes. carefully stopper the test tubes to ensure the liquids do not spill out. (b) when operating the centrifuge, students should do which of the following? make sure that the lid is completely shut and the safety knob is turned to engage the safety switch. centrifuge for approximately 30 minutes. centrifuge for approximately 30 seconds. mid-way through the process, open the lid of the centrifuge and check to be sure it is operating. (c) when the centrifuge process is complete, students should do which of the following? wait for the rotor to come to a complete stop before attempting to remove your test tubes. using the eyehole on top, monitor the spinning rate and open the lid only after the rotor has slowed significantly. immediately open the lid of the centrifuge to remove the test tubes before they are damaged. reach out and carefully slow the rotor with your hand so you may finish the lab faster.