Q. 183.7( 15 Votes )

Answer the following questions:

(a) A steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor: current, current density, electric field, drift speed?

(b) Is Ohm’s law universally applicable for all conducting elements? If not, give examples of elements which do not obey Ω ’s law.

(c) A low voltage supply from which one needs high currents must have very low internal resistance. Why?

(d) A high tension (HT) supply of, say, 6 kV must have a very large internal resistance. Why?

Answer :

(a) When a steady current flows in a metallic conductor of non-uniform cross section, the current flowing through the conductor is constant.


Since Current density, electric field and drift speed are inversely proportional to area of cross section therefore they are not constant.


(b) No, Ω ’s law is not applicable for all conducting elements. Example of non Ω ic conductor is Vacuum diode semiconductor.


(c) According to Ω ’s law V = I × R


If Voltage V is low, then Resistance R must be very low so that high current can be drawn from source.


(d) A high Tension supply must have a very large internal resistance so that it can limit the current from exceeding the safety limit.


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