question_answer 18)

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 Ohm's law. (c) A loss 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) Current, as it given to be steady. The other quantities depend inversely upon area of cross-section.                 (b) No. The non ohmic devices are vacuum tubes, semiconductor diodes, transistors, thermistors, thyristors etc.                 (c) Maximum current drawn                                 Clearly low r will ensure high current                 (d) If internal resistance is not large, then the heavy current drawn during accidental short circuit, can damage the soppy.