🔙 Prerequisite Revision:
👉 Chapter 13: Nuclei (Binding Energy & Radioactivity)Chapter 14: Semiconductor Electronics
Vol 1: Energy Bands & Classification
Energy Band Theory: In a crystal, atomic orbitals overlap to form continuous energy bands.
- Valence Band (VB): Band occupied by valence electrons (Highest energy filled band).
- Conduction Band (CB): Band where electrons are free to move (Empty or partially filled).
- Energy Gap ($E_g$): The gap between VB and CB where no electrons can exist.
| Type | Metals (Conductors) | Semiconductors | Insulators |
|---|---|---|---|
| Band Structure | VB and CB overlap. | Small Gap ($E_g < 3 \text{ eV}$). | Large Gap ($E_g > 3 \text{ eV}$). |
| Examples | Cu, Al, Ag | Si ($1.1$ eV), Ge ($0.7$ eV) | Diamond ($6$ eV), Wood |
Vol 2: Doping - N-type & P-type
Doping: The process of adding a desirable impurity to a pure (intrinsic) semiconductor to increase its conductivity.
N-type Semiconductor
• Dopant: Pentavalent (Group 15) like Arsenic (As), Phosphorus (P).
• Carriers: Electrons are Majority, Holes are Minority.
• Mnemonic: N-type = Negative electrons = ND (Donor).
P-type Semiconductor
• Dopant: Trivalent (Group 13) like Indium (In), Boron (B).
• Carriers: Holes are Majority, Electrons are Minority.
• Mnemonic: P-type = Positive holes = PA (Acceptor).
Vol 3: P-N Junction & Biasing
When a P-type semiconductor is joined to an N-type, a Depletion Region is formed (devoid of free charges).
Biasing of Diode
- Forward Bias: P-side to Positive, N-side to Negative. Depletion layer decreases. Current flows easily. (Ideal Resistance = 0).
- Reverse Bias: P-side to Negative, N-side to Positive. Depletion layer increases. No current flows. (Ideal Resistance = $\infty$).
Vol 4: Application - The Rectifier
Rectification: The process of converting AC (Alternating Current) into DC (Direct Current).
2. Full Wave Rectifier: Uses 2 Diodes (Center Tap). Converts both halves of AC cycle. Efficiency $\approx 81.2\%$.
Vol 5: Logic Gates (Digital Electronics)
Building blocks of digital circuits. (0 = Low/OFF, 1 = High/ON).
| Gate | Symbol | Boolean Expression | Function |
|---|---|---|---|
| OR | Curved D | $Y = A + B$ | Addition (1 if any input is 1) |
| AND | Straight D | $Y = A \cdot B$ | Multiplication (1 if all inputs 1) |
| NOT | Triangle + Bubble | $Y = \bar{A}$ | Inverter (Reverses input) |
| NAND | AND + Bubble | $Y = \overline{A \cdot B}$ | Universal Gate |
Vol 6: Final Mission 100 Question Bank
Section A: MCQs
Q1. At absolute zero temperature (0 K), a semiconductor behaves as:
(a) Superconductor (b) Conductor (c) Insulator (d) Semiconductor
Ans: (c) Insulator.
Q2. In a forward biased P-N junction, the width of depletion layer:
(a) Increases (b) Decreases (c) Remains same (d) Becomes infinite
Ans: (b) Decreases.
Section B: Conceptual (3 Marks)
Q3. Explain why Photodiodes are always operated in Reverse Bias.
Ans: In reverse bias, the current is due to minority carriers. When light falls, electron-hole pairs are generated. The fractional change in minority carrier current is much larger and easier to detect than the fractional change in majority carrier current (Forward bias). Hence, sensitivity is higher in Reverse Bias.
Section C: Diagram Based
Q4. Draw the circuit diagram of a Full Wave Rectifier and explain the role of the Center Tap Transformer.
Ans: (Refer to Vol 4). The center tap transformer allows the two diodes to conduct in alternate half cycles, ensuring current flows in the same direction through the load.
🎉 Mission 100 Physics Completed! 🎉
Congratulations! You have completed the entire Class 12 Physics Syllabus.
From Electrostatics to Semiconductors — Your "Mahagranth" collection is now ready.
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