activity to demonstrate the fact that for a metallic wire of uniform material density and thickness, the resistance increases directly with its length.

Answer 1

By "activity" I assume you want to carry out an esperiment.

All you need is an ohmeter and a wire of long length. You can put the probes at different points along the wire (at different wire distances apart) and measure the ohms. The wire does not have to be straight, but coils should not touch each other, if the wire is not insulated.

You will get more accurate results by cutting various lengths of wire and assuring good contacts at the ends. Alligator clips would help.

Plot length vs measured resistance on a graph.