Explain the effect of forward bias on a p-n junction. Draw its circuit diagram and its forward I-V characteristic, and mark the threshold voltage.

1. 1 · Define forward bias. The p-side is joined to the positive terminal and the n-side to the negative terminal.
2. 2 · Explain the effect. The barrier falls to V₀ − V and the depletion region narrows, so majority carriers cross and current flows.
3. 3 · Draw the circuit. [Circuit: battery, rheostat as potential divider, diode with p to +, milliammeter in series, voltmeter across the diode]
4. 4 · Draw the curve. [Graph: I (mA) against V (V); almost zero until about 0.7 V, then rising steeply; threshold voltage marked]
5. 5 · Real life. An LED glows only when forward biased.
6. 6 · Close in one line. So, a forward-biased diode conducts easily once the threshold voltage is crossed.

Scoring tip: Use a milliammeter, not a microammeter, in the forward-bias circuit, and write the threshold value on the graph.