Codes :List – I List – II a. Shot Noise i. Resistance b. Johnson Noise ii. Diode c. Current Noise iii. P-N junction d. Partition Noise iv. Triode
a-ii, b-i, c-iii, d-iv
Each noise mechanism belongs to a particular kind of device, and two of the four links are beyond dispute.
(b) Johnson noise → (i) resistance. Also called thermal noise, it arises from the random thermal motion of carriers in any resistive element and exists whether or not current flows:
\(V_{n}=\sqrt{4kTBR}\qquad P_{n}=kTB\)
Its association with resistance is definitional, so any option not pairing b with i is wrong — which eliminates options 2 and 3 at once.
(a) Shot noise → (ii) diode. Shot noise is caused by the discreteness of charge: carriers cross a potential barrier one at a time and at random instants, so the current fluctuates about its mean:
\(I_{n}=\sqrt{2qI_{DC}B}\)
Schottky derived it for the vacuum diode, and it applies to any device where carriers cross a barrier independently. Between options 1 and 4, this pairing is what decides the answer.
(d) Partition noise → (iv) triode. Partition noise appears when a stream of carriers divides between two or more electrodes, since the split is statistical. It is a valve phenomenon — strictly it needs more than two electrodes, which is why a pentode is noisier than a triode — and in solid-state devices its counterpart is the division of emitter current between base and collector in a BJT.
(c) Current noise → (iii) P-N junction. Current noise, also called flicker or \(1/f\) noise, has a spectral density inversely proportional to frequency and is caused by carriers being trapped and released at defects and surface states — abundant at a semiconductor junction. It dominates below a few kilohertz, which is why low-frequency and DC amplifiers are chopper-stabilised.
So a-ii, b-i, c-iii, d-iv — option 4.
| Noise | Cause | Spectrum |
|---|---|---|
| Johnson | Thermal agitation in a resistance | White |
| Shot | Discrete carriers crossing a barrier | White |
| Flicker / current | Trapping at defects | 1/f |
| Partition | Statistical division of a carrier stream | White |
The answer is flagged for confirmation because "current noise" and "shot noise" are used loosely in some texts, and a key treating current noise as the P-N junction's shot noise would swap (a) and (c).
Hence, the correct match is a-ii, b-i, c-iii, d-iv.
Similar Questions
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1. Input noise voltage
2. Equivalent noise resistance
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4. Noise figureSelect the correct answer.
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A. G1 = 10 dB
B. G1 = 20 dB
C. G1 = 50 dB
D. G1 = 30 dB
E. G1 = 40 dB
Choose the correct answer from the options given below :
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(a) Industrial noise is usually of impulse type.
(b) HF mixers are generally noisier than HF amplifiers.
(c) Thermal noise is independent of frequency at which it is measured.
(d) Impulse noise voltage is independent of the bandwidth.
Which of the above statements are correct ?
Assertion (A) : Noise figure is defined as the ratio of the signal to noise power at the input terminal to the signal to noise power at the output terminal of the system.
Reason (R) : The noise figure will be less than 1 for an ideal receiver, which introduces no noise of its own.
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1. Input noise voltage
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