# Search results

1. ### Dulong Petit derivation.How do we get this formula?E=kT

Is that because in an atom in a solid, there are 6 neighbors so, (6/2)${k_B}$ T
2. ### Signal to noise ratio for thermal and shot noise

10000 electrons without telling time, but even telling time, I still can calculate the thermal and shot noise.
3. ### Signal to noise ratio for thermal and shot noise

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?
4. ### Signal to noise ratio for thermal and shot noise

Homework Statement 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. Homework Equations SNR= 10 log (power of signal/ power of noise) Or...
5. ### Quantum mechanics , total orbital angular momentum?

##\vec{L}^2## mean the angular momentum square ##L_z## angular momentum in z direction ##\vec{L}^2##=l(l+1)\hbar and ##L_z##=m\hbar. Total orbit angular momentum is j? J=l-(1/2) or l+(1/2)
6. ### Quantum mechanics , total orbital angular momentum?

Homework Statement A hydrogen atom is identified as being in a state with n=4. What is the magnitude of the total orbital angular momentum for the largest permitted value of l? Homework Equations n>l, l is bigger or equal to m The Attempt at a Solution The allowed l= 3,2,1 The allowed m for...
7. ### How does FET amplifier amplify?

Thank you. If I want to calculate the output impedance, I have to off the input signal, yet there are still 2 dc supplies ,one to gate-source, another is the $V_cc$ , and there should be current pass though , but my book said $g_mV_{gs}$ =0? From the picture you gave,
8. ### How does FET amplifier amplify?

BJT ,the output voltage is amplified because there is dc voltage supply to keep BJT active ,but what about the FET? The voltage supplied only control the gate only, anything to do with the output? Thanks

10. ### Shannon entropy - use to calculate the bit needed to encode a symbol

To encode a symbol in binary form, I need 3 bits ,and I have 6 symbols. So I need 6*3=18 bits to encode "We are" into binary form. As shown in http://www.shannonentropy.netmark.pl/calculate My question: 3 bits to encode one then I have to use 16 bits, _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _. How to...
11. ### From Planck's law to derive the stefan Boltzman constant.

The following is the Planck's derivation for black body radiation $${\rho}({\lambda}) d{\lambda}=E({\lambda})*f({E(\lambda}))*D({\lambda})d{\lambda}------equation 1$$ $$\int_0^\infty{\rho}({\lambda})d{\lambda}$$ is the density of radiative energy. From...
12. ### Derivation for black body radiation. What is the 2 bout?

Can you please explain more? How two taps to empty a water tank? Water go from taps to tank then? How should I prove the two polarization modes? Please tell me. Thanks.
13. ### Derivation for black body radiation. What is the 2 bout?

$${\rho}({\lambda}) d{\lambda}=E({\lambda})*f({E(\lambda}))*D({\lambda})d{\lambda}$$ $${\rho}({\lambda}) d{\lambda}$$ is density of radiative energy, $$E({\lambda})= k_BT$$ is the energy of an atom vibrate in 3D, $$f({E(\lambda}))=1$$ is the probability distribution. Equals to 1 because we...
14. ### Dulong Petit derivation.How do we get this formula?E=kT

Dulong Petit use energy,E=$k_B$T and the probability distribution as f(E)=1. Internal energy,u=3N$k_B$T $$C_v=∂u/∂T=3NkT$$ Three there because there is 3 modes in each atom. Then my question is why do we use E=kT? I understand 1 atom has 3 degree of freedom,and 1 freedom has kT/2. A...
15. ### Refractive index- will it travel back along the same way?

Sorry, it is spectrometer. Yup it is use to find the refractive index of the glass cell. My book says : a sharp boundary distinguishes the bright from the dark region because no rays are refracted with an angle of refraction larger than critical angle. So ? I think the refraction will occur...
16. ### Refractive index- will it travel back along the same way?

No, I am using spectroscopy and prism to detect the refraction index.
17. ### Refractive index- will it travel back along the same way?

Then is this picture correct? This is an experiment to find the region n2 refractive index
18. ### Refractive index- will it travel back along the same way?

Refractive index----- will it travel back along the same way? From the picture http://en.wikipedia.org/wiki/File:RefractionReflextion.svg If I travel a light ray from n2 to n1 , I think the light ray will travel in the opposite direction shown in the first picture. But what about the...
19. ### Monostable multivibrator no input, the transistor1 in active mode?

Thanks, guys If there is no negative pulse ,the whole circuit is only powered by Dc ,and there are capacitor inside, how will the current flow?
20. ### Monostable multivibrator no input, the transistor1 in active mode?

If there is no pulse, and the whole is only supply with Dc and there are capacitors inside, how will the current move?
21. ### Monostable multivibrator no input, the transistor1 in active mode?

If T1 is in active mode all the time, will there be any current flow in this circuit? ( I think it is impossible to flow) thanks
22. ### Bound state of a square well, no allowed bound state mean?

I am sorry, but I am still confused. No need to keep E constant, because the interception point I want is $${\u_o}$$ (from Wikipedia ) . But I still wonder how to find out the minimum voltage? $${u_ o} < {\frac{\pi}{2}}$$ then solve for minimum V.
23. ### Bound state of a square well, no allowed bound state mean?

But less than pi/2 doesn't mean it must have one interception point with the even parity, then .....?
24. ### Bound state of a square well, no allowed bound state mean?

Thanks. Bound state also refer to the wavefunction $\psi_n$. Just to confirm: my solution for the question is (pa/z)< (pi/2) ,solve for minimum V
25. ### Bound state of a square well, no allowed bound state mean?

Thanks for replying. So my answer is (-pa/z)< (pi /2), by keeping the energy constant and the solve for the minimum V. One more to ask, actually what does it mean no bound state ? I wonder what is the physical meaning of no bound state? No wave function?
26. ### Bound state of a square well, no allowed bound state mean?

Homework Statement Show in the graph ,there will be no allowed bound states with odd-parity if the well depth is less than ${V_min}$ Find ${V_min}$ in terms of k and a.where a is the half of the well width. What does no allowed bound state mean? Homework Equations $cotz=-pa/z$ where p^2...
27. ### Bound state of finite square well, why do we make this statement?

The exponential function ( is not complex ) here doesn't represent wave that is why no wave outside the well. But why do we have exponential function outside the well? What does it represent?
28. ### Bound state of finite square well, why do we make this statement?

Why there is no incident wave ,yet we still have exponential function?
29. ### Bound state of finite square well, why do we make this statement?

One more to ask, for bound state, do we still have wave transmitted and reflected? No enough energy to transmit? What is the negative energy mean?
30. ### Bound state of finite square well, why do we make this statement?

Thanks Yup, it is scattering state. So it doesn't mean we don't have wave from the right, we take only left for simplicity. Reflected means bounce back, but in this scattering state, there is no potential wall or any wall, why the wave bounce back?