(a) Circuit Arrangement for V-I Characteristics
Step 1 (Circuit Components & Setup): [1 Mark]
To study the V-I characteristics, the p-n junction diode is connected in two configurations: Forward Bias and Reverse Bias. The circuit requires a DC power supply, a potentiometer (to vary voltage), a milliammeter (for forward current $I_f$), a microammeter (for reverse current $I_r$), and a voltmeter (to measure potential difference $V$).
Description of Diagram:
- Forward Bias: p-terminal connected to positive, n-terminal to negative.
- Reverse Bias: p-terminal connected to negative, n-terminal to positive.
(b) Shape of V-I Characteristics
Step 2 (Graphical Representation): [1 Mark]
The V-I characteristic curve is non-linear. In forward bias, current increases exponentially after the knee voltage ($V_k$). In reverse bias, a negligible leakage current flows until the breakdown voltage ($V_{br}$) is reached.
$$I = I_0 \left( e^{\frac{eV}{nkT}} - 1 \right)$$Where $I$ is the diode current, $V$ is the applied voltage, and $I_0$ is the reverse saturation current.
(c) Information Derived from Characteristics
Step 3 (Deductions): [1 Mark]
- Dynamic Resistance ($r_d$): It is the ratio of small change in voltage to the corresponding small change in current: $r_d = \frac{\Delta V}{\Delta I}$.
- Knee Voltage ($V_k$): It identifies the threshold voltage at which the diode starts conducting significantly (approx. $0.7\text{ V}$ for Si and $0.3\text{ V}$ for Ge).
💡 EL10 Concept Insight:
Think of a diode like a one-way turnstile at a park; it lets current flow easily in one direction once you push hard enough (Forward Bias), but it locks up tight if you try to go the other way (Reverse Bias), only breaking if you push with extreme force.