Semiconductor Devices

Step 1: Diamagnetic behavior.
Diamagnetic substances create an induced magnetic field in the direction opposite to the applied magnetic field. This causes a force that tends to align the substance in a direction where it minimizes energy.
Step 2: Orientation of the rod.
For a thin diamagnetic rod suspended in a uniform external magnetic field, it aligns itself perpendicular to the magnetic field. This minimizes the potential energy of the system, as the magnetic moment opposes the external field.
Step 3: Conclusion.
The rod will align itself perpendicular to the magnetic field, so the correct answer is (A).

Step 1: Analyze diode behavior.
Identical diodes will have equal potential difference only if both are either forward biased with equal current or reverse biased identically.

Step 2: Examine circuit (C).
In option (C), both diodes are forward biased symmetrically, ensuring identical current and hence equal potential difference across each diode.

Step 3: Final conclusion.
Thus, the circuit in which both diodes have equal non-zero potential difference is option (C).

Step 1: Write initial centripetal force.

Step 2: New speed and radius.

Step 3: Write new centripetal force.

Step 4: Simplify the expression.

Step 5: Compare the two forces.

Step 6: Find the change in force.
Decrease in force =

Step 7: Conclusion.
The centripetal force decreases by of its original value.

Step 1: Use Einstein’s photoelectric equation.

Step 2: Substitute given values.

Step 3: Relation with stopping potential.

Step 4: Conclusion.
The stopping potential is .

Step 1: Relationship Between , , and .
In a transistor, the relationship between collector current , base current , and is given by: where is the emitter current. The emitter current is related to the base current by: From this, we can calculate the base current as: Substituting the given values: Step 2: Final Answer.
Thus, the base current is 30 .

Step 1: Understanding Barrier Potential in Diodes.
In a semiconductor diode, the barrier potential opposes the flow of current by impeding the movement of free electrons in the n-region. The majority carriers (electrons in n-region and holes in p-region) are unaffected by the barrier potential, but the minority carriers (electrons in p-region and holes in n-region) face resistance due to the potential.
Step 2: Final Answer.
Thus, the barrier potential offers opposition to free electrons in the n-region.

Step 1: Analyzing the circuit.
The circuit consists of an OR gate followed by a NOT gate (inverter). The OR gate gives the output , and the NOT gate inverts the output to produce .
Step 2: Boolean expression.
The output of the circuit is given by the expression , and the NOT gate inverts it. The final Boolean expression is .
Step 3: Conclusion.
The correct Boolean expression is , corresponding to option (A) OR gate.

Step 1: Understanding depletion layer.
In an unbiased p-n junction, electrons from the n-side and holes from the p-side diffuse across the junction and recombine.

Step 2: Charge carrier distribution.
Due to recombination, mobile charge carriers (electrons and holes) are removed from the junction region.
Only immobile ions remain in this region.

Step 3: Conclusion.
Thus, the depletion layer is depleted of free electrons and holes.

Step 1: Gauss's Law.
According to Gauss's law, the total electric flux through a closed surface is proportional to the charge enclosed inside the surface. The electric flux is given by: where is the charge enclosed and is the permittivity of free space.
Step 2: Behavior of flux with balloon size.
Since the charge is uniformly distributed over the surface and the charge itself does not change as the balloon inflates, the total electric flux remains constant.
Step 3: Conclusion.
The total electric flux remains unchanged as the balloon increases in size, so the correct answer is (B).

Step 1: Understanding photodiodes.
A photodiode is a semiconductor device that operates in reverse bias. When light hits the junction, it generates electron-hole pairs, which contribute to the photocurrent. This current is directly dependent on the incident radiation.
Step 2: Conclusion.
The correct answer is (D), as photodiodes are always operated in reverse bias to generate photocurrents.

Step 1: Identify individual gates.
The first two gates and are NOT gates, so they invert inputs and .

Step 2: Analyze the final gate.
The outputs of the NOT gates are fed into an OR gate with an inverted output, i.e., a NOR gate.

Step 3: Write Boolean expression.


Step 4: Apply De Morgan’s theorem.


Step 5: Conclusion.
The resultant gate is AND gate with Boolean expression .

Step 1: Understanding the relation.
In a common emitter configuration, the collector current is related to the emitter current by the following relation: Where is the current gain of the transistor. Given that the current gain is and the emitter current , we can find the collector current. Step 2: Calculating the collector current.
Thus, the correct answer is (D) .

Step 1: Understanding the behavior of depletion region.
The width of the depletion layer in a p-n junction diode depends on the biasing conditions. - In forward bias, the width of the depletion region decreases because the external voltage reduces the barrier for charge carriers to cross the junction. - In reverse bias, the width of the depletion region increases as the applied voltage enhances the barrier, making it harder for charge carriers to cross. Step 2: Conclusion.
Thus, the width of the depletion layer decreases under forward bias and increases under reverse bias. Therefore, the correct answer is (D) decreases and increases.

Step 1: Understanding the band gap.
In insulators, the band gap between the valence band and the conduction band is very high, making it difficult for electrons to move into the conduction band. This is why insulators do not conduct electricity.
Step 2: Analyzing the options.
- (A) very high, empty: Correct, because in insulators, the conduction band is empty, and the band gap is large. - (B) very low, partially filled: Incorrect, this describes conductors or semiconductors. - (C) very high, completely filled: Incorrect, the conduction band remains empty in insulators. - (D) very low, empty: Incorrect, the band gap is high, not low.
Step 3: Conclusion.
The correct answer is (A), because insulators have a very high band gap and an empty conduction band.