1. ### Electric field and electric potential exercise

a) \vec{F}=\vec{E}\cdot q \phi =\oint \vec{E}d\vec{S}=\oint \vec{E}d\vec{S}=\underbrace{\oint \vec{E}d\vec{S}}_{\textrm{FACES } \perp}+\underbrace{\oint \vec{E}d\vec{S}}_{\textrm{FACES } \parallel}=0+\oint EdS\cdot \underbrace{\cos 0}_1= E2S \dfrac{Q_{enc}}{\varepsilon_0}=\phi \left...
2. ### Induced EMF in a moving Loop Conductor

I am having trouble figuring out if the circular loop has an induced current. One explanation is ∫ E ds = -d Φ / dt. Since flux = B ⋅ A, a change in the magnetic field would require a change in the magnetic field, a change in the area, or change in direction of either vector. Since none of...
3. ### Flux due to a charge located at the corner of a cube

The correct answer is B, but I am not sure why. I have a few confusions regarding this problem. First of all, I had thought that we cannot use Gauss' Law to determine the flux through a SIDE of a cube since Gauss' Law only works for SURFACES. How can we determine how an electric field pierces a...
4. ### B Intensity of Spherical Shell of Stars

Given that L is the luminosity of a single star and there are n stars evenly distributed throughout this thin spherical shell of radius r with thickness dr, what is the total intensity from this shell of stars? My calculations were as follows: Intensity is the power per unit area per steradian...
5. ### I Does an AC Magnetic field induce movement in a DC Magnetic Field?

Summary: Can a rotating AC Magnetic field induce movement in a static DC Magnetic flux? I'm designing a control panel, and the customer has asked us to reduce the EMC as much as possible; there are no drives, or other noise creating devices, just AC circuits. I thought a good starting point...
6. ### Checking divergence theorem inside a cylinder and under a paraboloid

I am checking the divergence theorem for the vector field: $$v = 9y\hat{i} + 9xy\hat{j} -6z\hat{k}$$ The region is inside the cylinder ##x^2 + y^2 = 4## and between ##z = 0## and ##z = x^2 + y^2## This is my set up for the integral of the derivative (##\nabla \cdot v##) over the region...
7. ### Flux linked with lower face of a cube

Homework Statement A point charge q is placed inside a cube of side 2a. What will be the flux associated with the lower surface ABCD? Homework Equations I think I can apply Gauss Law here, but can't think of something connecting it with the lower surface. ∫B.dl = 1/ε° X Charge Enclosed The...
8. ### Flux Through a Cube's Face with our Point Charge at a Corner

Homework Statement A charge q is placed at one corner of a cube. What is the value of the flux of the charge's electric field through one of its faces? Homework Equations The flux surface integral of an electric field is equal to the value of the charge enclosed divided by the epsilon_naught...
9. ### Mass Transfer: are both convective mass transfer and eddy diffusion the same?

I have studied that mass transfer is of two types Molecular mass transfer(diffusion) Eddy diffusion then in later portion of the book I found that there is convective mass transfer too, I wanted to ask if both convective mass transfer and eddy diffusion are same ? I read this equation N_i =...
10. ### Magnitudes and Comparison

Homework Statement You have decided to use a CCD camera to check if a 16th magnitude quasar is variable. With your telescope/camera combination, you know that a star with a magnitude of 0 would deliver 1 × 109 photons/second to one pixel, so this allows you to work out the photons/second from...
11. ### Transport phenomenon

My book states that when a flow around object is considered, Non dimensional momentum flux is defined as the drag coefficient In case of flow through tubes it states The non dimensional momentum flux is defined as the friction factor What do these statements mean? What do they practically...
12. ### Magnetic field and flux

Homework Statement [/B] There is lead XY shaped as straight wire. Next to it, circular lead with radius 0.10 m. They are in the same plane. XY to center of circle, O is 0.20 m. Curent flowing through XY is 15.7 A Homework Equations The Attempt at a Solution 1) find magnetic field (B) at...
13. ### Calculating flux with a magnet and a coil

Homework Statement [/B] Hey, I'm having some difficulties with my physics project and I hoped someone could help me out. We have to calculate the magnetic field, but first we need to know the flux. This is the setup we got: We have to let a magnet fall through a PVC tube. The tube has a coil...
14. ### Magnetic flux in a white dwarf

Homework Statement The sun has a rotational period of 25 days. Finding the rotational period if it can shrink to form a white dwarf (##R_{WD}=10^3Km##). Knowing that the density of magnetic flux of the Sun on the surface is ##1 Gauss##, finding the magnetic flux of the white dwarf. Homework...
15. ### What is the direction of the current in the given image?

Homework Statement In the picture 20.40, what is the direction of the current induced in the resistor at the instant the switch is closed.[/B] Homework Equations Right hand rules- Point thumb in direction of current and your fingers will curl in direction of magnetic field. Lenz's law. The...
16. ### Wire loop falling out of a magnetic field

Homework Statement Here is a link to the problem: https://imgur.com/a/0T9sF I am having trouble finding the time it takes the loop to leave the field in part a. Homework Equations ## emf=-\frac{d \Phi}{dt} ## ## \Sigma F=ma=mg-BIl ## ## \frac{dv}{dt}-\gamma v=g ## where ##...
17. ### I Understanding Gauss' law: diff b/w E and D flux?

I noticed the other day something odd in how we use Electric and Magnetic flux. The definitions I refer to are magnetic flux density (B), magnetic flux intensity (H), electric displacement field (D) or Electric field density (D) and electric field (E): B = μH ΦB = B*Area & D = εE ΦE = E*Area...
18. D

### Electric Flux through Cubical Surface Enclosing Sphere

Homework Statement A uniform charge density of 700 nC/m3 is distributed throughout a spherical volume of radius 6.00 cm. Consider a cubical Gaussian surface with its center at the center of the sphere. [reference picture] What is the electric flux through this cubical surface if its edge...
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21. ### What force does the current carrying coil feel?

Homework Statement What direction does the force that the current carrying coil feel point to when a magnetic field is turned on? A magnetic field is turned on and points from bottom to top and passes through a current carrying coil that has current passing through it CCW. Here is a diagram...
22. ### Calculating the mutual coupling coefficient of E cores

Hi, I can't find my inductance calculations book. Say that you were considering magnetic flux linkage more from a geometric perspective: -Does the mutual coupling coefficient for a series of coils all on the same steel core add up to a maximum total of ~1? Because I tried simulating a three...
23. ### Mutual inductive coupling

Hi, I have a couple of questions regarding re-wiring a three phase transformer. Say you have a three phase TX with a ratio of 415:22 and you want to use it as a single phase step-up TX (excite it with a variac or something), this is a thought-experiment. If you excited only the middle leg of...
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### B Flux dependant upon the number of turns?

https://atarnotes.com/forum/index.php?topic=144870.msg953546#msg953546 http://i.imgur.com/XtCj6OP.png (worked solution on left and plain answer on right; they aren't the same and neither take into account the number of turns, which adds to the confusion) Is the book's answer correct? Doesn't...
25. ### Electric Flux through a Net

Homework Statement [/B] A butterfly net hangs from a circular loop of diameter 400 mm . You hold the loop horizontally in a region where the electric field is 150 N/C downward, as shown in (Figure 1) . What is the electric flux through the net? Homework Equations k = 9E9 N E = kq/r2 Flux = Q...
26. ### I Magnetic alignment of steel question

Hi, I have a question about steel, for instance, silicon steel used in magnetic cores. I was wondering about how Iron magnetises: can you align the grains/domains and heat treat it [or anything], so that it responds differently to flux one way then the other direction? For example, say you...
27. ### I Building speakers, induction and induced current

i made a speaker from a cup, a coil of wire and a magnet. I hooked up both of the ends of the wire to a headphone jack and it works. Albeit very low sound, but it works. Can you point me in the direction of some equations that will show me the most influential factors on how to make it louder...
28. ### A question on E Flux and Fields

Homework Statement 1. The field for an infinite charged sheet is found to be σ/2ε0. If we place 2 infinite sheets of opposite charge above one another, we say that the field in between the sheets is σ/ε0 due to the superposition of individual fields. Why can't we say the same for a situation...
29. ### B Does the first maxwell equation apply only...

For static electric fields? does it apply also for a generic electric field? Let's say, moving charges inside a closed surface? If there are charges accelerating in a closed surface a part of the electric field is due to the charges, and a a part is due to the fact that the charges acceleration...
30. ### Magnetic Flux Through a Square Loop

Homework Statement A loop of wire in the form of a square 1.50 m on each side, its plane makes an angle of 40.0° with a uniform magnetic field of 0.95 T. What is the magnetic flux through the loop? Homework Equations Φ = BAcosθ A = s^2 The Attempt at a Solution I found the area of the square...