(a) (i) Define mobility of electrons. Give its SI units. (ii) A steady current flows through a wire AB, as shown in the figure. What happens to the…

Mobility: Mobility is defined as the magnitude of the drift velocity per unit electric field.

\[\text { S.I. Unit: } \frac{m^{2}}{V . s} \text { or } \frac{C . s}{k g} \] (ii) Both electric field and the drift velocity decreases. Justification:

\[v_{d}=\frac{I}{n e A} \] As area increases across the wire, drift velocity decreases.

\[v_{d}=\frac{e E}{m} \tau \] As drift velocity decreases, electric field decreases (since e ,m and \(\displaystyle \tau\) are constant). (iii) From the diagram \(\displaystyle 10 \Omega\) and \(\displaystyle 14 \Omega\) are in series \(\displaystyle \mathrm{R}_{1}=10 \Omega+14 \Omega=24 \Omega 10 \Omega\) and \(\displaystyle 10 \Omega\) are in series \(\displaystyle \mathrm{R}_{2}=10 \Omega+10 \Omega=20 \Omega\)