Write down an expression for the resistance of a metallic wire in terms of the resistivity.

What do you understand by the "resistivity" of a substance?

A wire is 1.0 m long, 0.2 mm in diameter and has a resistance of 10 Q. Calculate the resistivity of its material?

What will be the resistance of a metal wire of length 2 metres and area of cross-section 1.55 x 10^-6 m², if the resistivity of the metal be 2.8 x 10^-8 Ω m ?

Give two examples of substances which are good conductors of electricity. Why do you think they are good conductors of electricity?