I can understand that if its a string, then since it is tired there should be a node. Also, for sound waves, since the particle near the wall cannot oscillate, there should be a node. But, in electromagnetic waves, it just has a varying electric and magnetic field. Why it should form a node at the walls ( like in radiation in a cavity)
The electric field parallel to a conductor must be zero. That's like "holding the string" but for electric fields.
Because at wall electric field and magnetic field becomes will pass through inter space between molecules so it make node with low amplitude