Physics

Problem

Two cylindrical wires, A and B, carry the same current. Wire A (copper) has radius

r

and free-electron density

n

. Wire B (a doped semiconductor) has radius

\tfrac{1}{2}r

and charge-carrier density

0.2n

. If

v_{dA}

and

v_{dB}

are their respective drift velocities, what is the ratio

\dfrac{v_{dB}}{v_{dA}}

? a)

5

10

20

4