two wires each of radius of cross section r but of different materials are connected together end to end (in series). If the densities of charge carriers in the two wires are in the ratio 1:4, the drift velocity of electrons in the two wires will be in the ratio:
paritoshdragonz:
hello abhishek, I wanted to know regarding how the answer came out be 4:1
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Answered by
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Let, the drift velocities of the wires be vd and vd' respectively.
Area of cross- section of two wires be A and A'.
Then,
A : A' = 1:4
This implies,
A' = 4A
i) When the two wires are connected in series, the same amount of current flows through both the wires.
Implies,
n A vd e = n A' vd' e
where,
n is the number of electrons per unit volume and,
e is the charge on electron.
Therefore,vd=A'A =4A
A=4:1
vdvd' = A'A = 2AA = 2 : 1
ii) When the two wires are connected in parallel, the potential difference across the two wires would be the same.
Area of cross- section of two wires be A and A'.
Then,
A : A' = 1:4
This implies,
A' = 4A
i) When the two wires are connected in series, the same amount of current flows through both the wires.
Implies,
n A vd e = n A' vd' e
where,
n is the number of electrons per unit volume and,
e is the charge on electron.
Therefore,vd=A'A =4A
A=4:1
vdvd' = A'A = 2AA = 2 : 1
ii) When the two wires are connected in parallel, the potential difference across the two wires would be the same.
this is the wrong answer
the answer is 4:1, it was a very silly mistake really, I make em too sometimes
nAvde = neA' Vd' e
this will become Vd/Vd' = A'/A
i.e Vd/Vd' = 4A/A = 4:1 :)
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