(a) Define conductivity and mobility.
Answer:
(b) Define static and dynamic resistance of a p-n junction.
Answer:
(c) Explain the principle of LED.
Answer: Light Emitting Diodes work on the principle of electroluminescence. When a p-n junction is forward biased, electrons cross from the n-side to the p-side and holes cross from the p-side to the n-side. During recombination, energy is released in the form of photons (light).
(a) Explain in detail both forward and reverse bias characteristics of a p-n junction diode.
Answer:
Forward Bias: When the P-region is connected to the positive terminal and N-region to the negative terminal. The depletion layer narrows, allowing current to flow exponentially after the knee voltage.
Reverse Bias: When the P-region is connected to the negative terminal and N-region to the positive terminal. The depletion layer widens, preventing majority carrier flow.
(b) Why is the current during reverse bias called reverse saturation current?
Answer: It is called "saturation" current because it reaches a constant maximum value very quickly and remains independent of the applied reverse voltage (until breakdown). It is caused by the flow of minority carriers.
Explain input and output characteristics of a transistor in CE mode.
Answer: In Common Emitter (CE) mode, the emitter is common to both input (base) and output (collector).
In a CB configuration, I_E = 1 mA. If emitter is open, I_C = 60 μA. Find I_C if α = 0.9.
Answer:
Given: I_E = 1 mA = 1000 μA, α = 0.9, I_CBO = 60 μA (current when emitter is open).
Formula: I_C = α I_E + I_CBO
I_C = (0.9 × 1000) + 60
I_C = 900 + 60 = 960 μA.
(a) Why are h-parameters called hybrid parameters?
Answer: They are called "hybrid" because they use a mix of units. For example, h_ie is measured in Ohms (impedance), h_fe is dimensionless (current gain), and h_oe is in Siemens (admittance).
(b) Difference between virtual ground and real ground.
Answer:
Real Ground: Physically connected to the earth/zero potential point.
Virtual Ground: A point in a circuit (like the inverting input of an OP-AMP) that is not physically grounded but is at zero potential because the other input is grounded and gain is infinite.
| A B C | Minterm (Symbol) | Maxterm (Symbol) |
|---|---|---|
| 0 0 0 | A'B'C' (m0) | A+B+C (M0) |
| 0 0 1 | A'B'C (m1) | A+B+C' (M1) |
| 1 1 1 | ABC (m7) | A'+B'+C' (M7) |
(Simplified table; full list includes all 8 combinations)
.Explain J-K Flip-flop and Race Around Condition.
Answer: The J-K Flip-flop is a universal flip-flop that eliminates the invalid state of an S-R flip-flop. Race Around Condition: Occurs in Level-triggered J-K flip-flops when J=1, K=1, and the clock pulse width is greater than the propagation delay of the gate. The output toggles multiple times during a single clock pulse, leading to an uncertain state.