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CBSE Class 12-science Answered

P1 p2
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Asked by alanpeter9611 | 18 Feb, 2019, 11:16: PM
answered-by-expert Expert Answer
Current I  in a conductor of cross section A is related to drift velocity as given below
 
I = n e vd A  .......................(1)
 
where n is number density of electrons and e is the chatge of electron.
 
when two conductors are in series, same current flows through the conductors.
 
hence     vd1 A1 = vd2 Aor   vd1 / vd2 = A2 / A1 
 
When two conductors are connected in parallel, currents in conductor are given by
 
begin mathsize 12px style I subscript 1 space equals space fraction numerator I space R subscript 2 over denominator R subscript 1 plus R subscript 2 end fraction space space space a n d space space I subscript 2 space equals space fraction numerator I space R subscript 1 over denominator R subscript 1 plus R subscript 2 end fraction end style
where I is total current. R1 and R2 are resistances of respective conductors
 
hence begin mathsize 12px style I subscript 1 over I subscript 2 space equals space R subscript 2 over R subscript 1 end style  .......................(2)
since R is inversely proportional to area and using eqn.(1), we write eqn.(2) as ,     begin mathsize 12px style fraction numerator v subscript d 1 end subscript A subscript 1 over denominator v subscript d 2 end subscript A subscript 2 end fraction space equals space A subscript 1 over A subscript 2 space space space o r space fraction numerator begin display style v subscript d 1 end subscript end style over denominator begin display style v subscript d 2 end subscript end style end fraction space equals space 1 end style
Answered by Thiyagarajan K | 20 Feb, 2019, 10:15: AM
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