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Define the terms (i) drift velocity, (ii) relaxation time.A conductor of length L is connected to a d.c. source of emf epsi . If this conductor is replaced by another conductor of same material and same area of cross-section but of length 3L, how will the drift velocity change ? |
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Answer» Solution : (i) Drift velocity : Drift velocity is the AVERAGE uniform velocity acquired by conduction (free) electrons inside a metal by the application of an electric FIELD which is responsible for current through it. (ii) Relaxation time : Relaxation time is the average time between successive collisions of conduction electrons with heavy fixed ions inside a metal when a current flows through it on applying an electric field. The average is taken over a large number of collisions. The drift velocity of electrons through a current carrying conductor is given by the relation `I =epsi/R =n A e v_d "or" v_d = (epsi)/(RnAe)` where `v_d`is the drift velocity and R the resistance of given conductor. If instead of a conductor of length L we USE another conductor of same material and same area of cross-section but of length 3L, then resistance of new conductor will be R. = 3R (since resistance of a conductor is directly proportional to its length). New drift velocity `v_d = (epsi)/(R. nAe) = (epsi)/((3R) nAe) = (v_d)/(3)` |
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