question_answer 65)

  What is electrical resistivity? In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 5A. The reading of the ammeter decreases to half when the length of the wire is doubled.' Why ?

Answer:

                  The electrical resistivity of a material is defined as the resistance of a conductor made of that material of unit length and unit cross-sectional area. The resistance of an uniform conductor is given bywhere,  is the length of the conductoris the electrical resistivity of the material A is the cross-sectional area. If  is doubled, then R is also doubled. So, in this case,   Since,                    So,                        when, R is doubled, I becomes.