A potential divider circuit is connected with a dc source of $$20 \mathrm{~V}$$, a light emitting diode of glow in voltage $$1.8 \mathrm{~V}$$ and a zener diode of breakdown voltage of $$3.2 \mathrm{~V}$$. The length (PR) of the resistive wire is $$20 \mathrm{~cm}$$. The minimum length of PQ to just glow the LED is _________ $$\mathrm{cm}$$.

From the given transfer characteristic of a transistor in $$\mathrm{CE}$$ configuration, the value of power gain of this configuration is $$10^{x}$$, for $$\mathrm{R}_{\mathrm{B}}=10 ~\mathrm{k} \Omega$$, and $$\mathrm{R}_{\mathrm{C}}=1 ~\mathrm{k} \Omega$$. The value of $$x$$ is __________.

A $$8 \mathrm{~V}$$ Zener diode along with a series resistance $$\mathrm{R}$$ is connected across a $$20 \mathrm{~V}$$ supply (as shown in the figure). If the maximum Zener current is $$25 \mathrm{~mA}$$, then the minimum value of R will be _______ $$\Omega$$.

If the potential barrier across a p-n junction is $$0.6 \mathrm{~V}$$. Then the electric field intensity, in the depletion region having the width of $$6 \times 10^{-6} \mathrm{~m}$$, will be __________ $$\times 10^{5} \mathrm{~N} / \mathrm{C}$$.