Question

what is rheostat and variable resistance?give examples?are they ohmic or non ohmic materials?

Answer 1

Rheostat is a coil with variable nodes. So, when you move along a rheostat, the resistance can be changed as we move along.
Its made of a conductor which is ohmic and the position of the nodes decides the resistance that a rheostat offers.
As resistance depends upon length and area. as length changes, resistance changes.