If the current flowing in a copper wire be allowed to flow in another copper wire of same length but of doubled the radius, then what will be the effect on the drift velocity of the electrons. If the same current be allowed to flow in an iron wire of the same thickness, then ?

Explanation

We know that if two wires are in series, there will be same current in each wire. The current I through the wire is related with drift velocity `v_(d)` by the relation
`I= n A e v_(d) or A v_(d)=a` constant
or `v_(d) prop 1/A or v_(d) prop (1)/(pi r^(2))`
Since in the second wire, the radius of wire becomes 2 times hence the drift velocity will bacome one fourth. In case of iron wire, the number density of free electrons will be less in comparison to copper wire and hence the drift velocity will be more in comparison to that in copper wire.