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Two wires X,Y have the same resistivity, but their cross-sectional areas are in the ratio `2 : 3` and lengths in the ratio `1 : 2`. They are first connected in series and then in parallel to a.d.c. source. Find out the ratio of drift speeds of the electrons in the two wires for the two cases. |
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Answer» Correct Answer - `3;2;2;1` Given, `(A_(1))/(A_(2)) = (2)/(3) and (l_(1))/(l_(2)) = (1)/(2)` When two wire are in series , the current through two wires is the same As ` I = nAev_(d)` so , `upsilon_(d) = (1)/(nAe) or upsilon_(d) prop (1)/(A)` `:. (upsilon_(d_1))/(upsilon_(d_2)) = (A_(2))/(A_(1)) = (3)/(2)` When two wire are in parallel , the pot, diff `V` is same across each wire .Then `1 = (V)/(R ) = nAe upsilon_(d) or upsilon_(d) = (V)/(nAeR) = (V)/(nAe rhol//A)` or `upsilon_(d) = (V)/(n e rhol) or upsilon_(d) prop (1)/(l)` `:. (upsilon_(d_1))/(upsilon_(d_2)) = (l_(2))/(l_(1)) = (2)/(1)` |
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