When current flows through a conductor of tapered cross-section, current flow through every section remains constant.
$\Rightarrow I_1=I_2$
$\Rightarrow j_1 A_1=j_2 A_2$
$\Rightarrow \frac{j_1}{j_2}=A_2 < 1$
$\Rightarrow A_1$
$\Rightarrow j_1 < j_2$
Current density increases in the narrow region.
$\text { Also, } j=n e v_d$
$\Rightarrow n e v_{d_1} < n e v_{d_2}$
$\Rightarrow v_{d_1} < v_{d_2}$
Drift velocity increases in the narrow region.
and $\quad j=\frac{E}{\rho}$
where, $\rho=$ resistivity of material.
$\Rightarrow \frac{E_1}{\rho} < \frac{E_2}{\rho} \Rightarrow E_1 < E_2$
Electric field magnitude increases in the narrow region.
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