Dear, it is easy to draw on a copy as the dimension is much smaller than the whiteboard or blackboard. This is just a simple demonstration...

@@AnuragTiwariphysicshala sir, but smooth curve nahi aata, aur french curve use karne ke baad bhi curves seperate hi dikhte hai....

Same

​@@AnuragTiwariphysicshala coph mai pin kaise chubaye??

Try with board pins or paper pin📍

In that way the tangent is at 90degrees for both major and minor axis , at all other points it is not 90 .

You can use any arbitrary length of thread but keep the distance of two focus shorter than the thread.

@@AnuragTiwariphysicshala the length of the string is just the distance between the 2 focii of the ellipse.

Thanks 🙂@@AnuragTiwariphysicshala

You can take any arbitrary distance ellipse will form as per that distance.