(a) Write the relationship between resistivity and resistance of a cylindrical conductor of length l and area of cross-section A. Hence derive the SI unit of resistivity. (b) Why are alloys used in electrical heating devices ?
What the resistance of a conductor depends on
Usually 3 marks a paper · mostly long answers and short answers · asked in 2 of the last papers
Notes are being written
The board questions below are real and complete — they come from the CBSE papers themselves. The written notes for this topic are still being prepared.
Board questions on this topic
2 from the CBSE papers we hold — the exact wording the board used.
(i) Write the relation between resistance R and electrical resistivity rho of the material of a conductor in the shape of cylinder of length l and area of cross-section A. Hence derive the SI unit of electrical resistivity. (ii) The resistance of a metal wire of length 3 m is 60 ohm. If the area of cross-section of the wire is 4x10^{-7} m^2, calculate the electrical resistivity of the wire. (iii) State how would electrical resistivity be affected if the wire (of part 'ii') is stretched so that its length is doubled. Justify your answer.