$[5$ marks$]$

Figure $1\mathrm{.}2$

For the circuit shown in Figure $1\mathrm{.}2,$ find an expression for the Norton short circuit current in terms of $\backslash (\backslash$boldsymbol$\{$R$\}\backslash )$ and $\backslash (\backslash$boldsymbol$\{$V$\}\backslash ),$ between the terminals $\backslash (\backslash$boldsymbol$\{$a$\}\backslash )$ and $\backslash (\backslash$boldsymbol$\{$b$\}\backslash ).($f$)$ For the circuit shown in Figure $1\mathrm{.}4$ the value of $\backslash ($ I$\_\{0\}=5\backslash$mathrm$\{$~mA$\}\backslash ).$ You may assume that before the transient given by the unit step function occurs the circuit has been in that state for a very long time. Sketch the expected change in voltage as a function of time between terminals $\backslash (\backslash$boldsymbol$\{$a$\}\backslash )$ and $\backslash (\backslash$boldsymbol$\{$b$\}\backslash ).$ You should clearly show the initial and final voltage and the value of the transient time constant for the circuit.