See my notes and let me know if you have more questions.
Unless the mail is delayed at the end of the term you should be OK. I have a few days after the deadline before I have to submit grades.
Dr. Smith:Here are some questions/worked out problems I have been working on or stumped with. My mom told me that I had to be done with the course on the 9th of Dec. This should not be a problem other than the lady here sending the test back to VHCC. It might arrive later than the 9th. Will this be a problem? Thanks for your help, I am doing all this prep becuase on the last test I felt very comfortable with the problems and did well on the test.
At what Kelvin temperature will the thermal energy of electrons be greater than the energy binding an n = 2 electron to the proton in a hydroge
I am not sure where to find this in the book, I did not seem to see this problem in the intro problems too. I am not sure how to do this problem.
The following is covered in the Class Notes as well as the text, but I believe it should appear on Test 4 rather than Test 3. Make a note and store this away for Test 4.
The thermal energy of a particle at temperature T is 3/2 k T (from Test 1 material).
The binding energy in a hydrogen atom is 13.6 eV / n^2, where n is the orbital (in this case n = 2).
Find an expression for the work done in moving a test charge between plates, the potential difference between the plates, and the capacitance of a parallel-plate capacitor with uniform separation d and plate area A when the plates carry charges of Q and -Q. Repeat for a spherical capacitor with inner radius r1 and outer radius r2, also carrying charges Q and -Q on the respective spheres
I am not too sure what you are asking for here: This is what I have so far, I am not sure if I am right or not. Work done = |W| = |q E | `ds
Potential difference = |W| / q = | E | `ds
intro problems and your text explain Gauss' Law and its application to spheres, line charges and plane charges.
For a plane charge you get E = 2 pi k sigma, where sigma is charge per unit area. There are two plates so the field in between is 4 pi k sigma.
You need to use this to obtain an expression for the work and the potential difference in terms of d, A and Q. You have work and potential difference in terms of E; the above is the missing step you need to take to find E.
And for the sphere, I think it would be something like The flux of a charge Q is 4 `pi k Q. When spread out over a sphere of radius r, the flux density is 4 `pi k Q / (area of the sphere) = 4 `pi k Q / (4`pi r^2) = k Q / r^2
The potential of a spherical charge distribution at any point outside the sphere is - k Q / r, where Q is the charge contained in the distribution. Inside the sphere the potential due to the charge on the sphere is zero.
What therefore is the potential just beyond the surface of the inner sphere, and the potential just before reaching the inner surface of the outer sphere?
What is potential difference between these points?
That is where I am at with this problem
A coil consists of 60 circular loops of wire each of radius .21 meters. The coil is in a uniform magnetic field with strength .0082 Tesla. The coil is rotated in such a way that at t = 0 the field makes an angle of 82 degrees with a perpendicular to the plane of the loop, while at t = .001 sec the field is parallel to the plane of the loop. What is the average voltage induced around the coil?
For this problem I am confused where to start. I am not sure exactly what formulas to work with mainly because of the times given. I looked at the intro problems but I can’t seem to get under this problem.
What is the flux through a single loop when the angle is 82 degrees from perpendicular?
What is the flux when the field is perpendicular?
By how much does the flux thru a single loop therefore change?
By how much does the flux of the entire coil therefore change?
What is the average rate of change of flux with respect to clock time? This is the average voltage.
An electron (mass 9.11 * 10^-31 kg) with velocity directed to the North passes through a magnetic field of .0092 Tesla directed vertically upward, crossed with an electric field of 64000 N/C directed either East or West. The electron passes through undeflected. Is the electric field directed East or West, and how fast is the electron moving? What force does the electron experience from each field?
I know you would use force | = | q v B | to find the force the electron experiences.
The force exerted by the electric field is q E. You know q and E so you can find this force.
The electron passes thru the field undeflected, so the force q v B exerted by the magnetic field is equal and opposite to the force exerted by the electric field.
You know B so you can find v.
Would you find centripetal acceleration, F / m = q v B / m then? This is what I am not sure about for this problem.
If the electric field wasn't there, the net force would be q v B and your strategy would give you the centripetal acceleration, which you should recall is equal to v^2 / r.
However in this case the particle is undeflected, so centripetal acceleration would be 0. The electric field counters the magnetic field, which would otherwise cause a centripetal acceleration.
The direction of the magnetic force is given by the right-hand rule. This is explained with gestures in the Class Notes, and with good pictures in the text. The fingers of your right hand go in the direction of q * v, with your palm oriented so that when you close your hand your fingers will move toward the direction of B. Your thumb points in the direction of the force.
The electric force is in the direction opposite the magnetic force.
A generator has an internal resistance of 38 ohms, creates a potential difference of 3.8 volts. The generator is connected to an uncharged capacitor with capacitance .88 Farad in series with a bulb whose resistance is 47 Ohms. Approximately how long will it take to charge the capacitor to .1 * 3.8 volts? Describe what would happen during this time to two voltmeters, one connected across the bulb and another across the capacitor. Describe what would happen to an ammeter connected in series within the circuit.
I am not sure where to start this problem. I looked at the intro problems, but I got no real useful info to start this problem.
You have a potential difference of 3.8 volts and series resistances of 38 ohms and 47 ohms, so you should be able to find the current. From the current you can find the voltage drop across both resistances.
Set 53 problems 5 and 6 are relevant to finding the time it takes to build the charge. Check those problems out carefully and let me know if they don't help.
When the capacitor is uncharged, it has no voltage.
When it has built up to .38 volts, what will be the voltage across it?
This voltage is opposed to the voltage of the generator. So how much voltage will there now be across the two resistances, and how much current will be flowing?
What now is the voltage drop across each resistance?
A straight wire segment is .9 cm long and carries current 17 amps. A vector from the center of the segment to point P is perpendicular to the segment and has length 17 cm. Find the magnetic of the field at P due to the segment.
This is Set 54 Problem 2. Check out the solution in the Intro Problem Sets then let me know specifically what is and is not clear.
I am not sure how to incorporate the vector into this problem to get an answer, I started it but I would get stuck and my values were not looking right. So I think I am just doing the problem wrong. SO I am going to see what you have to say on this and then work with what I have.
A sensitive balance shows that a force of .0073 Newtons is exerted on a straight wire 4 cm long carrying a current of 4.1 amps by a uniform magnetic field directed perpendicular to the wire. What is the strength of the field? If the force is to the East and the current runs to the South, what is the direction of the field?
I seem to be having trouble with this type of problems, I have trouble reasoning out where to start and how to tell what direction the field will be, I just need help on this one.
Fingers are in the direction of the current, palm oriented so the fingers will turn from the direction of the current toward the direction of the field. Thumb points in the direction of the force.
Find the force on a 2.3 `microCoulomb charge at ( 3.159 m, .563 m) due to a charge of -8.901 `microCoulombs at ( 7.658 m, .189 m).
First you would do: 7.658 – 3.159 = 4.5 (dx)
.189 - .563 = -.374 (dy)
Distance is = `sqrt( ( 4.5 m)^2 + ( .374 m)^2 ) =4.5 m
The force would be: k * q1 * q2 / r^2 = (9 * 10^9 N m^2 / C^2) * | 2.3 * 10^-5 Coulombs | * | -8.901 * 10^-5 Coulombs | / ( 4.5 meters)^2 = 4.09 N
That's how to get the magnitude of the force. Force is a vector so you also have to be able to find the direction.
You have `dx and `dy. The direction of the corresponding vector is arcTan(`dy/`dx), plus 180 deg if `dx is negative.
The field will be either in this direction or opposite this direction, and you should be able to tell from a picture and which it is. The force will point in the direction of the force exerted on a positive test charge.
A beam consisting of 70 eV electrons (electron mass 9.11 * 10^-31 kg) is incident on a thin wafer of a crystal with layer spacing 2.4 Angstroms. Surprisingly we find that the electrons, which are particles, are scattered in such a way as to form an interference pattern identical to that of a wave. What will be the distance between central interference maxima at a distance of 12 cm from the wafer?
This problem has got me completely stumped, I am not sure how to go about doing this problem.
this problem is also apparently a refugee from Test 4; it would not be counted on Test 3.
A wire loop has radius 19 cm and carries current 11 amps. What is the magnitude of the magnetic field at the center of the loop?
Would you start this by first doing:
2`pi r = 2`pi ( .19 m) = 1.19 m
1.19 * 11 amps = 13.09 Amp meters
B=k ' (IL)/r ^ 2 = (.0000001 Tesla / Amp meter)( 13.09 Amp m)/( .19 m) ^ 2 = 3.6 * 10^-5 Tesla
Right. Good work.