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.
Assertion (A): The temperature coefficient of resistance is positive for p-type semiconductors and negative for n-type semiconductors.
Reason (R): The effective charge carriers in p-type semiconductors are electrons and in n-type semiconductors 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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All semiconductors (p-type or n-type) have a negative temperature coefficient of resistance, so (A) is false. In p-type semiconductors, majority carriers are holes, and in n-type, they are electrons. Reason (R) swaps these, so it is also false. Thus, both (A) and (R) are false.
Assertion (A): The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature decreases exponentially with increasing band gap.
Reason (R): It is more difficult for the electrons to jump to the conduction band from the valence band if the band gap between them is large.
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 true: The probability of finding electrons in the conduction band is proportional to \(e^{-E_g / (2kT)}\), decreasing exponentially with band gap \(E_g\).
Reason (R) is true: A larger band gap means more energy is required for electrons to jump. Reason (R) correctly explains Assertion (A).