Forward and Reverse Bias — Prelims Strategy
Prelims Strategy
To excel in NEET questions on forward and reverse bias, a multi-faceted strategy is essential. Firstly, master the definitions and their implications: clearly differentiate how each bias affects the depletion region, potential barrier, and charge carrier movement.
Use mental images or simple diagrams to reinforce these concepts. For numerical problems, especially those involving circuits, always start by identifying the bias condition of each diode. If forward biased, assume a voltage drop equal to its cut-in voltage ($0.
7, ext{V}0.3, ext{V}$ for Ge) and apply Kirchhoff's laws or Ohm's law to the rest of the circuit. If reverse biased, treat it as an open circuit (zero current) unless breakdown is explicitly mentioned.
Pay close attention to the polarity of connections; a common trap is misinterpreting the positive and negative terminals. For conceptual questions, focus on the 'why' behind the changes – why does the depletion region narrow in forward bias?
Why does current increase exponentially? Understand the role of both majority and minority carriers. Practice questions involving I-V characteristics to quickly identify regions and key parameters.
Finally, be prepared for questions on temperature dependence of reverse saturation current, remembering the doubling rule for every rise. Always check units and significant figures in numerical answers.