This is probably a question with every induction cooktop user. And to answer this question, I would have to ask you one small question. Consider a hypothetical scenario where you are presented with a sphere and a cube and you are asked to step onto them one at a time and count to 10 before you step down.
Which one do you think would be easier to step on? Yes, it will be way easier to step on the cube than on the sphere. Why so? The cube has a flat base that makes it more stable while sphere as its circular warped base is wobbly. Similar is the case with induction cooktops. Understanding the reason why flat-bottomed pans are more suitable for induction cooks tops do not require you to be physicist ‘cause it is not rocket science.
It is simple physics. The more the area of contact, the more evenly is the heat distribution and the quicker the dish gets cooked, making it more energy and time efficient. Furthermore, in an induction cooktop, the fluctuating magnetic fields that it produces need to pass through the cookware, so, the closer the cookware is to the induction to surface, the more lines pass through it. Also, it is always more advisable not to use a pan or a pot with a roundish base for safety reasons.
Cooking in a utensil that is unstable and wobbly is quite dangerous. An induction cooktop does not have burners and holders that keep the utensil steady, hence if you try to use a vessel with a roundish base over the smooth flat top of the induction cooktop, chances are that the vessel might roll over while you are trying to stir-fry the ingredients.
When and if it does roll over, your hand, arm and other body parts that are in close proximity may get hurt. A couple of induction cooktop models are designed in a fashion that they are not compatible at all with utensils that have a roundish base. If you do buy such a model and place a rounded based pot over it, you may hear a beep sound or it may even refuse to start the heating process.