Signal to noise ratio for thermal and shot noise

1. Jan 10, 2014

Outrageous

1. The problem statement, all variables and given/known data
The output of a sensor which produces 10000 electrons is connected to parallel RC circuit with Resistance= 50 ohm, and the capacitance=10pF.
Calculate the signal to noise ratio at temperature 300K.

2. Relevant equations
SNR= 10 log (power of signal/ power of noise)
Or SNR = 20log ( voltage signal / voltage noise)

3. The attempt at a solution
Voltage=C/Q=624.15V
Power of signal= voltage square / resistance= 7791.2 J
But how to calculate power of noise? The thermal noise = 4kTf, where k is boltzman constant, f is frequency bandwidth. Yet not given , but I can only think of these formula for thermal noise and 10000 electron need to include shot noise?

2. Jan 11, 2014

marcusl

Check your equation for the voltage on a capacitor--it's not quite right. Then use this hint: the noise bandwidth is determined by the RC filter.

3. Jan 11, 2014

rude man

Is that 10,000 electrons or 10,000 electrons per second?

4. Jan 11, 2014

Outrageous

Yup, V =Q/C , and f=1/(2∏RC)
But why is this the Bandwidth? The impedance of capacitor is same as resistance so we get maximum power for?
And 10000 electrons need to consider shot noise? If I consider, so I just add thermal noise voltage and shot noise together to get the total voltage noise?

5. Jan 11, 2014

Outrageous

10000 electrons without telling time, but even telling time, I still can calculate the thermal and shot noise.