A little known fact about microwave ovens is that the magnetron is either on or off. When a microwave is set for 50% power, the magnetron is switched off half the time. Usually 20 seconds or so at a time.
Here's what AI says:
In a microwave oven, the duty cycle refers to the ratio of "on" time to the total cycle time of the magnetron, the device that generates microwaves. To achieve lower power settings, microwaves don't actually reduce the magnetron's power output, but rather cycle it on and off at varying intervals. This creates an average power level that is lower than the full power output of the magnetron