91Ó°ÊÓ

• Unwanted sound that is regarded to be unpleasant, loud, or disruptive to hearing is referred to as noise.
• Noise is indistinguishable from sound in terms of physics, as both are vibrations across a medium such as air or water.

It is necessary to explain the many types of noise that have varied frequency dependences.

There are two types of noise that impair analysis:

1. Chemical noise

2. Instrumental noise

• Chemical noise is caused by uncontrollable variables that have an impact on the chemistry of the system under investigation. Temperature, pressure, chemical equilibria, humidity, light intensity, and other unnoticed fluctuations are examples.
• Instrumental Noise: Each component of an instrument is related with noise, including the source, input transducer, signal processing elements, and output transducer.

Noise is a complicated mixture that is difficult to adequately quantify. Certain types of instrumental noise are prohibited.

3. Shot noise

4. Flicker Noise:

• Flicker noise is defined as noise whose size is inversely proportional to the frequency of the measured signal. It's also referred as as$\frac{1}{\mathrm{f}}$ noise. The cause of flicker noise is unknown; however it can be identified by its frequency dependency. When the frequency is less than approximately, flicker noise becomes noticeable 100 Hz . When compared to the more usual carbon composition type, flicker noise can be greatly reduced by utilising wire-wound or metallic film resistors.
• Shot Noise: When electrons or other charged particles cross a junction, shot noise occurs.

Where,${\mathrm{i}}_{\mathrm{rms}}$ root-mean-square current fluctuation,

I = average direct current,

Charge on the electron,$(1.60×{10}^{-19}\mathrm{C})$

Df = band width of frequencies.

• Only by lowering bandwidth can shot noise in a current measurement be reduced.
• The different sorts of noise that depend on frequency and an example were discussed.