Assertion (A): The number of electrons in n-type semiconductor is higher than the number of electrons in a pure silicon semiconductor.
Reason (R): The law of mass action is applicable only to n-type semiconductors.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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In n-type semiconductors, donor impurities increase the number of free electrons, making Assertion (A) true. The law of mass action (\(n_e n_h = n_i^2\)) is a fundamental principle applicable to all types of semiconductors (intrinsic, n-type, p-type), so Reason (R) is false.
Assertion (A): The conductivity of an intrinsic semiconductor depends on its temperature.
Reason (R): No important electronic device can be developed using intrinsic semi conductor.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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In an intrinsic semiconductor, conductivity increases with temperature due to increased generation of electron-hole pairs. So Assertion (A) is true. Intrinsic semiconductors have limited practical use due to low conductivity, making Reason (R) true in terms of 'important' devices. However, (R) does not explain (A).
Assertion (A): Electron hole recombination takes place in P-region and N-region of PN Junction diode except in depletion region.
Reason (R): Electric field in depletion region oppose the diffusion.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is generally true in simplified models, where most recombination occurs in the quasi-neutral P and N regions. While some recombination does occur in the depletion region, its contribution to the overall current is often considered secondary for typical forward-biased diodes.
Reason (R) is true; the electric field in the depletion region acts as a barrier, opposing the diffusion of majority carriers across the junction. (R) does not explain the spatial distribution of recombination described in (A).
Assertion (A): Width of depletion region is reduced in forward bias.
Reason (R): In n-type semiconductor majority charge carriers are free electrons while in p-type they are holes.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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When a p-n junction is forward biased, the applied voltage counteracts the internal electric field, causing majority carriers to move towards the junction and reducing the depletion region's width. Thus, Assertion (A) is true.
Reason (R) correctly states the majority carriers in n-type (electrons) and p-type (holes) semiconductors, which is also true. However, Reason (R) does not explain why the depletion region width reduces under forward bias. Hence, both are true, but R is not the correct explanation for A.
Assertion (A): The drift current in a p-n junction is from n-side to p-side.
Reason (R): The diffusion current in a p-n junction is from p-side to n-side.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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In a p-n junction, the built-in electric field points from the n-side to the p-side, causing drift current to flow from n-side to p-side. Thus, Assertion (A) is true. Due to concentration gradients, diffusion current arises from the movement of majority carriers, resulting in a net diffusion current from p-side to n-side. Thus, Reason (R) is also true.
These are two distinct current mechanisms, and R does not explain A.
Assertion (A): P-type semiconductor has high density of holes in valence band while N-type semiconductor has high density of electrons in conduction band.
Reason (R): In N-type semiconductor, as the density of donor atoms (N_D) is increased, the fermi energy level shifts towards the valence band.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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P-type semiconductors have a high concentration of holes in the valence band, and N-type semiconductors have a high concentration of electrons in the conduction band. Thus, Assertion (A) is true.
In an N-type semiconductor, increasing the donor atom density (N_D) increases the electron concentration, causing the Fermi energy level to shift closer to the conduction band, not the valence band. Hence, Reason (R) is false.
Assertion (A): Generally npn transistors are widely used.
Reason (R): In npn transistor the mobility of majority charge carriers is more.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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NPN transistors are widely preferred because their majority charge carriers, electrons, have significantly higher mobility than holes. Higher electron mobility allows for faster switching speeds and better high-frequency performance, making NPN transistors generally more efficient and widely used. Therefore, Assertion (A) is true, Reason (R) is true, and R is the correct explanation for A.
Assertion (A): Conductivity of intrinsic semiconductor is less as compared to extrinsic semiconductor.
Reason (R): With increase in temperature conductivity of semiconductor increases.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Concept: Semiconductor conductivity.
Intrinsic semiconductors have fewer free charge carriers than extrinsic (doped) semiconductors, so (A) is true. Increasing temperature generates more carriers in semiconductors, increasing conductivity, so (R) is true. However, (R) describes temperature dependence, not the difference between intrinsic and extrinsic. Thus, (R) is not the correct explanation for (A).
Assertion (A): Semiconductors do not obey Ohm’s law.
Reason (R): Electric current is determined by the rate of flow of charge carriers.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Concept: Ohm's Law and current definition.
Semiconductors are non-ohmic devices, so (A) is true. Electric current is indeed the rate of flow of charge, \(I = \frac{dQ}{dt}\), so (R) is true. However, (R) is a definition of current and does not explain why semiconductors are non-ohmic. Thus, (R) is not the correct explanation of (A).
Assertion (A): The temperature coefficient of resistance is positive for metals and negative for semiconductors.
Reason (R): On raising the temperature, in metals drift velocity increases but in semiconductors more charge carriers are released.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Concept: Temperature dependence of resistance.
Metals have a positive temperature coefficient of resistance, while semiconductors have a negative one, so (A) is true. In metals, drift velocity *decreases* with increasing temperature due to increased scattering. In semiconductors, carrier concentration increases, so (R) is false.