No, you should not heat empty plates or any other empty containers in a microwave. Microwaving an empty plate can be potentially hazardous and may cause damage to the microwave oven.
When you heat food in a microwave, the microwave energy is absorbed by the water molecules present in the food, causing them to vibrate and generate heat. This is how the food gets heated. However, when there is no food or liquid to absorb the microwave energy, the energy has nowhere to go, and it can be reflected back to the magnetron (the microwave's energy source).
The reflected energy can build up in the microwave and potentially damage the magnetron or other internal components of the oven. It may also cause arcing, which is the visible discharge of electricity that can damage the interior of the microwave and create a fire hazard.
To avoid any potential hazards, always ensure that there is something in the microwave, such as food or a microwave-safe container with liquid, when you are using it. If you need to heat an empty plate for a short time, it's better to use alternative methods such as warming it in an oven or with hot water rather than using the microwave.