# Physics Class 12 NCERT Solutions: Chapter 14 Semiconductor Electronics Materials Devices and Simple Circuits Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q: 9. For a CE-Transistor amplifier, the audio signal voltage across the collected resistance of is . Suppose the current amplification factor of the transistor is , find the input signal voltage and base current, if the base resistance is .

Collector resistance,

Audio signal voltage across the collector resistance,

Current amplification factor of the transistor,

Base resistance,

Input signal voltage

Base current

We have the amplification relation as:

Voltage amplification

Therefore, the input signal voltage of the amplifier is .

Base resistance is given by the relation:

Therefore, the base current of the amplifier is .

Q: 10. Two amplifiers are connected one after the other in series (cascaded) . The first amplifier has a voltage gain of and the second has a voltage gain of . If the input signal is volt, calculate the output ac signal.

Voltage gain of first amplifier,

Voltage gain of second amplifier,

Input signal voltage,

Output AC signal voltage

The total voltage gain of a two-stage cascaded amplifier is given by the product of Voltage gains of both the stage, i.e.. ,

We have the relation:

Therefore, the output AC signal of the given amplifier is

Q: 11. A p-n photodiode is fabricated from a semiconductor with band gap of . Can it detect a wavelength of ?

Energy band gap of the given photodiode,

Wavelength,

The energy of a signal is given by the relation:

Where,

But

The energy of a signal of wavelength is , which is less than the energy band gap of a photodiode. Hence, the photodiode cannot detect the signal.

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