UJT is abbreviation for Unijunction Transistor made up of n type silicon material to which P-type emitter is used.UJT has three terminal namely Emitter (E), Base 1 (B1) and Base 2 (B2).

$R_{B1}$ and $R_{B2}$ are the internal resistance respectively from bases $B_1$ and $B_2$, to x-point.

When a voltage $V_{BB}$ is applied across the two base terminals $B_1$ and $B_2$, the potential of point x with respect to $B_1$ is given by,

$$V_{x} =I R{B_{1}}$$

$$= \frac{V_{B B}}{R_{B_{1}}+R_{B 2}}R_{B1}$$

$$=\frac{R_{B 1}}{R_{B 1}+R_{B 2}} V_{B B}$$

$$V_{x}=\eta V_{B B}$$

where $\eta=\frac{R_{B 1}}{R_{B 1}+R_{B 2}}$

$but \ R_{B B}=R_{B 1}+R_{B 2} \quad \therefore \eta=\frac{R_{B 1}}{R_{B B}}$

Where $\eta$ is the internal UJT voltage divider ratio and is called the intrinsic stand off ratio.