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Study the table given below: The above table gives I-V relationship for a manganin coil prepared from a wire of cross-section area 1 xx 10^(-7)m^2 and length 4.1 m.Now answer the following questions:(a) Does the maganin coil behave as an ohmic resistor ? (b) What is its electrical resistance ? (c) Determine the resistivity of manganin.(d) Compare the resistivity of manganin with that of copper.(e) Why do you consider manganin an ideal choice for preparing standard resistors ? |
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Answer» Solution : (a) Yes, manganin COIL behaves as an ohmic resistor because ratio `V/I`(i.e., the resistance R of the coil) is a CONSTANT for all the values of current ranging from 0.2 A to 8.0 A and if we plot a graphthen graph will be a linear graph. (b)Value of resistance of given manganin wire R = 1.95 `Omega` (c) Resistivity of manganin`rho = (RA)/(l) = (1.95 xx (1 xx 10^(-7)))/((4.1)) = 47.6 xx 10^(-8) Omega m` (d) Resistivity of manganin is much more than that of copper `(1.7 xx 10^(-8) Omega m)`. (e) From the table we observe that resistance of manganin coil remains unchanged even for aflow of very strong current of 8.0 A, when the coil will become quite hot. It MEANS that resistivity and hence resistance of a manganin coil remains practically unchanged and is not altered on changing the temperature. Due to this property we consider manganin an ideal MATERIAL for preparing standard resistors. |
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