Johnson and Shot Noise at 20*C with 9V Battery and 100Kohm Resistor

In summary, a 9V battery with negligible internal resistance is connected to a 100Kohm resistor. At a temperature of 20*C and a measurement bandwidth of 10KHz, the values of Johnson and shot noise can be calculated using Vrms = [4KTRB]^1/2 and Irms = [2eIB]^1/2 respectively. The temperature at which the Johnson and shot noise contributions to the noise voltage across the resistor become equal is assumed to be independent of temperature.
  • #1
Myrddin
25
0
A battery of emf 9V, and negligible internal resistance, has a 100Kohm resistor connected across its terminals. What are the values of johnson and shot noise at a temperature of 20*C if the measurement bandwidth is 10KHz?

At what temperature would the johnson and shot noise contributions to the noise voltage across the resistor become equal? [ assume that the resistor is independent of temperature]

Will put up my attempts later! any help would be good.
 
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  • #2
Ok can find johnson noise by Vrms = [4KTRB]^1/2 where k is boltzman constant, T is temperature R is resistance and B is bandwidth.

Show noise found by Irms = [2eIB]^1/2 so I am presuming shot noise is independent of temperature?
 
  • #3
Solved.
 

1. What is Johnson noise and how does it differ from Shot noise?

Johnson noise, also known as thermal noise, is the random fluctuation of electric current in a conductor due to the thermal energy of the surrounding environment. In contrast, Shot noise is the random variation of current caused by the discrete nature of charge carriers in a conductor. Johnson noise is present in all conductors, while Shot noise is only significant in systems with discrete charge carriers, such as semiconductors.

2. How is Johnson noise measured?

Johnson noise can be measured by connecting a resistor to a sensitive amplifier and observing the voltage fluctuations across the resistor. The magnitude of the noise is directly proportional to the resistance of the conductor and the temperature of the environment.

3. What factors can affect the level of Johnson noise?

The level of Johnson noise is affected by the resistance of the conductor, the temperature of the environment, and the bandwidth of the measurement system. Higher resistance and temperature lead to higher levels of Johnson noise, while a wider bandwidth can increase the signal-to-noise ratio.

4. How does Shot noise impact electronic devices?

In electronic devices, Shot noise can cause fluctuations in the output signal, which can affect the accuracy and precision of measurements. It is particularly significant in devices using low currents, such as photodetectors, as the discrete nature of charge carriers can result in significant noise levels.

5. How can Johnson and Shot noise be reduced?

The level of Johnson noise can be reduced by using lower resistance materials, operating at lower temperatures, and using a narrower bandwidth for measurements. Shot noise can be reduced by increasing the number of charge carriers or by using techniques such as averaging or filtering to reduce the impact of the noise on the output signal.

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