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• Users: kihr
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1. ### Effect on the width of the depletion region on doping level of an unbiased PN Jn.

One more thing. With a higher doping level the drift current should go up due to the higher electric field at the junction, and the diffusion current should go down due to the same reason. The net effect should be that the equilibrium condition would be attained faster in this case than if the...
2. ### Effect on the width of the depletion region on doping level of an unbiased PN Jn.

The concentration of ions goes up with increase in the doping level. Does this, therefore, imply that the width of the depletion region will increase for higher doping levels? It looks as if my initial thinking was not right.
3. ### Effect on the width of the depletion region on doping level of an unbiased PN Jn.

Homework Statement The problem is what would be the effect on the width of the depletion region of an unbiased PN junction on the doping levels of the P and N sides Homework Equations This is a conceptual question. There is no equation involved. The Attempt at a Solution Increase...
4. ### Nuclear Physics

The mass number alone does not give an indication of the charge. The problem does not state the atomic numbers. Had this been given the question of my doubt would not have arisen. Looking forward to further inputs from you. Thanks.
5. ### Nuclear Physics

Homework Statement An alpha particle is bombarded on 14 N. As a result a 17 O nucleus is formed, and a particle is emitted. This particle is a: (a) neutron (b) proton...
6. ### Nuclear Physics and binding energy

Going by the BEPN versus A (mass number) graph, in the case of fission (to which this problem appears to relate) the BEPN for the fission products is less than that of the parent nucleus. If this logic is to be applied A > B should be the correct answer. However, I understand that it is to be...
7. ### Nuclear Physics and binding energy

OK. Let me try out the way you have suggested.
8. ### Nuclear Physics and binding energy

Yes I do understand that in this case there would be a generation of energy because of the difference in rest masses between the parent and daughters. Also I am aware that energy would be conserved, and that this information would help in finding out, for instance, the kinetic energy of the two...
9. ### Nuclear Physics and binding energy

Homework Statement A nucleus of mass M + m1 is at rest and decays into two daughter nuclei of equal mass M/2 each. The binding energy per nucleon for the parent nucleus is A and that for the daughter nucleus is B. Which is greater A or B? Homework Equations Binding energy per nucleon=...
10. ### Electrostatics (Gauss's Law)

Yes. Could you please explain as to how to calculate the Coulomb force on q by q1 when the shell intervenes between the two? Do we have a situation of induction of a charge -q1 on the outer surface of the sphere, and a charge of +q1 on its inner surface due to induction? If this becomes clear...
11. ### Electrostatics (Gauss's Law)

Yes, but how to find out the directions of the field inside the shell due to the charge on the shell and also due to q1. I am still confused!
12. ### Electrostatics (Gauss's Law)

I would request for more elaboration on the concept of the net flux due to an external charge being zero, and also why there would be an electric field inside the sphere due to the charge q1. I took the electric field inside the sphere due to the charge on the sphere to be zero as I assumed...
13. ### Electrostatics (Gauss's Law)

Homework Statement A thin metallic spherical shell contains a charge Q on it. A point charge q is placed at the centre of the shell and another charge q1 is placed outside it. All the three charges are positive. Find (a) the direction of the force on the charge at the centre, and (b) the...
14. ### Capacitors and switches problem

Homework Statement Two capacitors, one with C1=2pF and V1=30V, and the other with C2=3pF and V2=20V are connected to each other through a switch (positive end of one connected to the negative end of the other). The other end of each capacitor is kept open. What happens to V1 and V2when the...
15. ### Optics homework help

By your method I don't get the answer given in the book. I guess either the answer given in the book is incorrect, or the approach to the solution may require a re-look.
16. ### Optics homework help

I could not quite follow the part regarding the combined focal length. Here we have only one lens (water) and one mirror. I would request for the explanation in a little more detail. Thanks.
17. ### Optics homework help

Homework Statement Water is poured into a concave mirror of radius of curvature R up to a height h. An object is placed along the principal axis at a distance x above the level of the water. What should be the value of x so that the image of the object is formed on itself? Homework...
18. ### Optics - Images with two convave mirrors

Thanks a lot.
19. ### Optics - Images with two convave mirrors

Yes in this case the answer should be 4f (i.e. 2f + 2f), and 2f should not be one of the solutions as given in the book. Would you also let me know in what way I have erred in applying the mirror formula to solve the problem. Thanks.
20. ### Where will the image of the candle be formed?

Thanks. I think the whole idea might have been to confuse the student!
21. ### Optics - Images with two convave mirrors

Homework Statement Two concave mirrors of equal focal length f are placed a distance d apart in air. A point source is placed midway between the two mirrors. What should d be so as to get only a single image? Homework Equations Mirror formula (1/f = 1/u + 1/v) The Attempt at a...
22. ### Where will the image of the candle be formed?

If we consider the surface of water as a mirror the answer is simple. But then what is the significance of giving the depth of the tank and the refractive index of water in this problem? This is what has confused me. Could you throw some light on this please?
23. ### Where will the image of the candle be formed?

Homework Statement A water tank is 4 meters deep. A candle flame is kept 6 metres above the level of the water. Mu for water is 4/3. Where will the image of the candle be formed? Homework Equations The Attempt at a Solution I need a few clues to proceed. If I consider refraction...
24. ### Voltmeter homework question

Thanks a lot for your help.
25. ### Voltmeter homework question

OK. Now if we consider a voltmeter grading of 2000 ohms / V, we get the value of external resistance as 24000 ohms. This being lower than the earlier value of 60000 ohms, is less preferred because the higher the resistance, the less the current drawn by the voltmeter. Trust this solution is in...
26. ### Voltmeter homework question

Homework Statement A voltmeter reads 8V at full scale deflection, and is graded according to its resistance per volt at full scale deflection as 5000 ohms / volt. How will you convert it into a voltmeter that reads 20V at full scale deflection? Will it still be graded as 5000 ohms / volt...
27. ### Electrostatic potential

Yes, but this is still not helping me to find the potential of the bigger sphere! This is because when I calculate the potentials of the two spheres and equate them (since the potentials are the same when they are in contact with each other) the potential of the bigger sphere cancels out. I...
28. ### Electrostatic potential

Homework Statement A spherical conductor of radius 2 m is charged to 120V. It is now placed inside another hollow spherical conductor of radius 6m. Calculate the potential to which the bigger sphere would be raised if the smaller sphere were made to touch the bigger sphere. Homework...
29. ### What is the work done by the electrostatic force

Homework Statement A spherical shell of radius 'a' and charge Q is expanded to radius 'b'. What is the work done by the electrostatic force in this process? Homework Equations Method 1 Work done = initial energy - final energy Method 2 Work done = Q (potential difference between...
30. ### Electric Dipole Moment of copper and sulphate ions

Homework Statement The electric dipole moment of a CuSO4 molecule is 3.2 * 10^-32 (i.e. 10 raised to the power of -32)C-m. Find the separation between the copper and sulphate ions. Homework Equations Electric deipole moment = 2aq where 2a=separation between the two charges q and -q...
31. ### Electromagnetic induction and alternating currents

Homework Statement A solenoid with an iron core inside it is connected in series with a resistance to a battery. What happens to the defelction in the ammeter connected in the circuit when the iron core is suddenly removed? Homework Equations Inductive reactance = wL Induced e.m.f. = -...
32. ### Binding energy per nucleon for atoms of low mass number

Thanks a lot for providing the clues.
33. ### Binding energy per nucleon for atoms of low mass number

Could you please quote the semi-empirical mass formula or refer me to the relevant web site? Thanks. Regarding the nuclear force it should be the same irrespective of the mass number given its very limited range (up to about 2.5 to 3 femtometres). In a heavy nucleus the coulomb repulsion...
34. ### Binding ehergy per nucleon for heavy nuclei compared to nuclei in the middle range

Homework Statement . Why does the binding energy per nucleon decrease with increase in mass number for heavy nuclei like 235 U? Homework Equations The loss in energy of the nucleons when they move from an unbound state to a bound state is the binding...
35. ### Graph of potential energy versus internucleon distance in an atom

Thanks. Let me have a look at your reference.
36. ### Binding energy per nucleon for atoms of low mass number

Could someone please explain to me as to why the binding energy per nucleon is lower for atoms of low mass number as compared to the atoms in the middle zone of the binding energy per nucleon versus mass number graph? My conceptual issue lies in the fact that when the mass number is low the...
37. ### Graph of potential energy versus internucleon distance in an atom

The graph of potential energy of a pair of nucleons as a function of their separation shows a minimum potential energy at a value r (approx. = 0.8 femtometers). Below r the PE is positive (actually rises sharply from a negative to a positive value). Above r the PE is negative, and becomes zero...
38. ### Drift speed of electrons and holes in semiconductors

My thinking is like this: A hole is not an independent entity, i.e.for a hole to be created we must have an electron jump from the valence band. Similarly for a hole to disappear an electron must recombine with a hole. In a n- type semiconductor, for example, an electron is free to move in...
39. ### Energy of electron in the hydrogen atom

I see the error. In case (b) U= +13.6 eV at r=infinity and NOT -13.6 eV as I had earlier calculated. Thanks a lot for your assistance.
40. ### Energy of electron in the hydrogen atom

U=-k*e^2 {Integ dr/r^2} (limits of integration from r=1.06A (where PE is zero) to r=infinity). Sorry for the strange mode of representation as I do not have a compatible keyboard!
41. ### Energy of electron in the hydrogen atom

I think now I understand it barring for the sign of work to be done. At r=infinity U = -13.6eV in case (b) {electron moved from r=1.06A corresponding to zero PE to r=infinity}. Since K=0 at infinity, total energy of the electron at r=infinity is -13.6eV. Therefore in order to free the electron...
42. ### Energy of electron in the hydrogen atom

I could not quite understand that. When the electron is unbound it is free, i.e. its total energy is zero. This is precisely its state at r=0.53A in case (b).
43. ### Energy of electron in the hydrogen atom

Consider this: At r=1.06A K=6.8 eV and U=0 {as per the new zero reference of P.E. as in case (b)}. Since E=0 at r=0.53A, the electron gains 6.8 eV of energy in moving from 0.53A to 1.06A. This means that when the electron is separated from its initial orbit to the orbit where U=0 it acquires...
44. ### Energy of electron in the hydrogen atom

Homework Statement Homework Equations The Attempt at a Solution . Homework Statement [/b] In a hydrogen atom the electron and proton are bound at a distance of about 0.53A. (a) Assuming the zero of potential energy at infinite separation of the electron from the proton...
45. ### Potential barrier in nuclear fusion

Having thought over it a little more based on your inputs, I think I have the answer to my problem. It is like this: When the two deuterons are moving towards each other, they have kinetic and potential energies which keep changing with time (I would assume that each has the same KE and PE...
46. ### Potential barrier in nuclear fusion

Thanks. Let me mull over your hints and try and figure out the whole issue.
47. ### Potential barrier in nuclear fusion

Homework Statement To calculate the height of the potential barrier for a head on collision between two deuterons given that each deuteron is a sphere of radius R Homework Equations Potential of the first deuteron at a distance of 2R from it =V = ke/2R where k = 9 * 10^9 , e= 1.6 *...
48. ### Endothermic nuclear reactions

Quote The weak force treats the two processes symmetrically. As a general rule in quantum mechanics, if a process can occur without violating conservation laws, then it will actually occur. Unquote Could you please elaborate further on the above? Does the weak force refer to force between...
49. ### Endothermic nuclear reactions

I now understand the issue somewhat better. Should the parent mass be less than the sum of the masses of the daughter and remaining products of the hypothetical reaction, the parent is a stable nucleus and will not spontaneously decay. The reaction could, however, take place if some external...
50. ### Endothermic nuclear reactions

OK. Could you also indicate as to how in a beta + decay, what is the source of the input energy that triggers the above reaction, i.e., transformtion of a proton into a neutron? Thanks