Emf Definition and 902 Threads

Homework Statement A rectangular coil of 90 turns has dimensions of 22 x 65 cm and is located in a uniform 1 T magnetic field. In 1.7 s, the plane of the coil is rotated from a position where it makes an angle of 19° with the magnetic field to a position where it makes an angle of 64°...

I have a question regarding a conducting loop of radius r in a changing magnetic field B. I understand and can determine the direction of the induced current which implies the existing of an electric field that is tangential to the loop. Since this is a closed loop, I am having trouble...

Say I have a solenoid that has a magnetic field Bo Sin(ωt) passing through its axis. What will be the EMF induced in the solenoid as a result ? I know it'll be a function of Cos (ωt) but I am more interested in how my choice of the solenoid will affect the EMF that I'll ultimately measure...

Hello everyone, I am trying to work on this topic as my research. i plan on using a potentiometer but i want to be able to use the resistor (across the test cell) as the load and still be able to obtain two balance points. one for emf, and another for calculating internal resistance as the cell...

Homework Statement A closely wound rectangular coil of 95.0 turns has dimensions of 29.0 cm by 40.0 cm. The plane of the coil is rotated from a position where it makes an angle of 39.0 degrees with a magnetic field of 1.60 T to a position perpendicular to the field. The rotation takes 0.120 s...

A hologram with "vibrational energy" to neutralize EMF radiation within its radius? http://www.safespaceprotection.com/qanda.aspx How do the products work? Our products 'repattern' the electromagnetic field by creating a 'coherent polarizing field effect'. When the charged particles are...

I have a discussion on how guitar pickup work, pickup is a coil with thousands of turns and magnet poles in the middle of the coil under each strings. My idea is the magnet poles magnetize a short portion of the string and when the string vibrates, it create a varying magnetic field. When the...

Homework Statement Calculate the EMF induced in a 5.0 cm by 2.5 cm rectancular coil containing 150 loops if it rotates at 28 Hz in a 0.014 T magnetic fieldHomework Equations Φ=BA ε=-N ΔΦ/Δt The Attempt at a Solution Φ=BA =.05m x .025m =1.25 x 10^-3 ε=-N ΔΦ/Δt =150 x (1.25x10^-3) /...

Homework Statement there is a cylindrical area in xy plane with a magnetic field (into the plane) that changes with time like that: (dB/dt)=δ the magnetic field outside the area is 0. the radius of the cylinder is a. we pick a string in the circle with lentgh L which is smaller than the...

In the example diagram I have provided how can the counter EMF produced by the conductor moving through the magnetic field be determined? I am assuming the field is uniform and that the velocity and current in the wire is constant. My logic tells me that there is no net flux cut by the...

Homework Statement I just conducted a lab for pchem where we took electric potential measurements with a volt meter in a solution for the reaction AgCl(s) +1/2 H2 (g) <--> HCl(aq) + Ag(s) We took the measurements using different concentrations of HCl. We were told that the...

Hello, While considering Faraday's Law of Induction, I tried to think of a situation which would expose some difficulties I have with the notion that there is an induced EMF without clear regions of relatively high and low voltage (as in a battery). Here is what I thought would get me started...

Homework Statement A bar magnet is dropped through a horizontal coil as shown below. An EMF is induced in the coil with the resultant voltage shown on the graph. Explain the shape of the graph, in particular the differences in the regions marked as A, B and C. Homework Equations...

In preparation for an upcoming physics exam I have been going through some past paper questions. This question is from the multiple choice section of the paper, so while I can check the answer there is no source from which I can see it being worked through. Homework Statement An aircraft...

Hi, I have a question about back emf So, my understanding of back emf (\epsilon_b=-L\frac{dI}{dt})is that its the counter voltage that's induced by change in current, whether it be from a battery or magnetic field (\epsilon_0). We can model this as an LR circuit where \epsilon_0 +\epsilon_b=IR...

Recently, someone I know has become convinced that the poor sleep I'm getting is the result of EMFs being emitted by anything near my bed that's electrical. I think this is complete ******** (Edit: look at that, the forum auto-censors). Although, if that was the end of the matter, I'd be...

Homework Statement In a lab I passed a magnet through a coil and measured the voltage. I need/want to know why when moving a magnet through a coil you induce a current. I don't necessarily need a direct answer - I more just want to know if my argument holds and where to look if I'm...

Homework Statement Are these two things not contradicting? Homework Equations The Attempt at a Solution See figure attached. Aren't these contradicting one another? They need a negative sign in there, correct?

Homework Statement See figure attached. Homework Equations The Attempt at a Solution If we attempt to solve part a) in this question we encounter several confusions. If we assume i(t) to be a positive current, the magnetic flux will flow through the core in a counter...

Homework Statement See figure attached. Homework Equations The Attempt at a Solution I'm having some confusion about the negative sign within this problem. If you compute the curl of the expression shown in the figure you'll find that it's equal to, -10v_{0} \hat{k} But...

Ok so I'm no pysichs buff, but could someone describe what the differences between Electromagnetic Radiation (Is this just a name for radiation?) and Electromagnetic Frequency (Do microwaves fall in this category aswell)? I basically would like to know the generic name of the devices (not brand...

Someone who knows what they are talking about: Show what the magnitude of induced emf Homework Statement Consider a magnetic field B = K(x3z2,0, -x2z3)sinωt in the region of interest, where K and ω are positive constants and t is variable time. Show that the magnitude of the induced emf...

If a loop is moved in a uniform magnetic field such that the direction of its motion is perpendicular to the magnetic field, then no change of flux occurs. Then according to faraday, no emf is induced... But I was thinking that can the emf be produced in it due to the deflection force?

Hi, When coil is excited with ac because of varying nature of current ,flux of varying nature will be developed in coil and because of varying flux emf will induce in coil. what will happen if coil is excited with dc? intially cureent will increase from zero to maximum and is...

A magnetic field points into the page. A conductive bar is moved to the right (perpendicular to the magnetic field). Why do the electrons move downwards toward the bottom of the bar? The book doesn't offer a good explanation of this... using right hand rule I would say that the electrons are...

Basic question on induced emf - ATTACHMENT CORRECTED PLEASE RE-READ Hi Please read the attached doc which is excerpted from the text University Physics by Young & Freedman.The discussion is on the emf induced in a loop made of a superconducting material when a magnet is moved towards it...

Homework Statement What potential difference is measured across a 23 ohm load resistor when it is connected across a battery of emf 7.99 V and internal resistance 0.555 ohms Answer in units of V Homework Equations V=IR V=emf - Ir The Attempt at a Solution V=IR emf-Ir=IR...

I attached the link to the problem. Shouldn't the Vlmax be 330V? I tried entering that and it wasn't accepting my answer.

I want to model a coil circuit with induced EMF. I want to verify that my model is correct in a circuit. That the voltage developed across the load is calculated correctly. From the equivalent circuit, you can see the current depend on the jX_L and it acts as a low pass filter in the complete...

Homework Statement Can someone please explain to me how to determine the direction of the veloicty of a bar that is conducting and inducing a current. Fb=q(VxB)?

Homework Statement Hello all, If we have a bar that is perpendicular to a magnetic field, and that bar is being pushed to the left via an applied force, all the while a current (due to a voltage source and resistor) runs down through the wire. Therefore, there would be a total force comprised...

Homework Statement A DC circuit which includes Emfx of unkown magnitude and orientation, at the location indicated is shown below. Note the 'ground' (V=0) in the circuit. The potential between 'b' and 'a', Vb-Va, is measured to be 2.00 V. a) The magnitude of Emfx is: b) Calculate...

[Solved] Estimate induced emf in the coil Homework Statement Consider a single-loop coil whose magnetic flux is given by this image: Estimate the induced emf in the coil at times near t = 0.3s, t = 0.4s and t = 0.5s This is for algebra-based physics. Homework Equations emf = -N*(change in...

Hello all, I'm not quite sure if this is a physics question or an EE question because it came up in an electronics design course for physicists with mostly engineering motivation, anyways here goes: I have an RLC band pass filter with a sinusoidal AC voltage input (Agilent function...

Hi, I've been thinking about the shape of the voltage waveform induced by a magnet falling through a coil. I know (both intuitively and from empirical experience) that the voltage should become increasingly positive as the magnet approaches the coil, then it should decrease rapidly...

Hi, I found this site with a calculation for EMF: http://www.6pie.com/faradayslaw.php. I just want to see if I have this right. Magnet Surface: Height (0.05 m) * Width (0.004 m) = Area 0.0002 m2. Coil windings: 6 Rotations per second: 5 NdFeB Magnet in N42 (1.33 Tesla) (I will reduce this...

Hi, I hope someone can help me. Looking at a magnetic generator, we will have a ring of magnets which will rotate, and then we have the copper wire static. I understand that if I have a ring of alternating magnets, all placed right next to each other, thereby creating a solid magnet surface...

when is terminal pd greater than emf ?

Hi, I wonder if someone can help me. Looking at magnetic generators, we spin the magnets around which will induce an EMF. This EMF will create a magnetic field opposite that of the magnets, thereby creating a drag. If I had to generate 1 watt for 1 second, how much kg force will I need to...

A 25-turn circular coil of wire has diameter 1.00 m. It is placed with its axis along the direction of the Earth’s magnetic field of 50.0 /T, and then in 0.200 s it is flipped 180°. An average emf of what magnitude is generated in the coil? This is a question in my book and the answer was...

Help me. I want to use diode for back E.M.F protection.Please help me to select diode which is suitable ,like short circuit recovery time is 9 nano second and ifsm should be 30-90 amp. please also send me surge suppression protection circuit or surge protection device.

Hi all, I'm a total noob when it comes to chemistry, and would need your help to understand the calculation of EMF for batteries. I have a couple of questions about the calculation for Zinc-Carbon batteries in Wikipedia: http://en.wikipedia.org/wiki/Zinc%E2%80%93carbon_battery I can't...

Homework Statement Two 9.4 k-ohm resistors are placed in series and connected to a battery. A voltmeter of sensitivity 1000 ohm/V is on the 3-V scale and reads 2 V when placed across either resistor. What is the emf of the battery? (Ignore it's internal resistance) Homework Equations...

I have got a doubt regarding the situation when a ring rolls in a non-uniform magnetic field. We can see that the flux linkage is increasing (considering dB/dt to be positive). So EMF should be induced in the loop. But if we join any two points, say the instantaneous axis of rotation and the...

Hi, What if the inductor coil is wound one way rather than the other. Then the circular flow of current will be clockwise in one case and anticlockwise in the other. And if the inductor is connected to an ac source, then the current will vary. Now in both the orientations, the variation...

How would one go about finding the EMF induced when a two-turn coil of wire is straightened into a one-turn coil?

Homework Statement suppose we have a coil sitting on a desk (with radius =1), and then a spark passes by the side of it, in such a way that the magnetic flux through the coil is maximized. The coil is attached to a full wave rectifier which is connected to a very large capacitor. There is an...

I'm doing a lab write-up for physics 2. The experiment is about the title, a bar magnet being dropped through a solenoid. I have to explain four graphs that plot the change in emf (y axis) vs. time (x) axis. There are incoming and outgoing peaks on these graphs. I have to tie these results...

I'm doing a lab write-up for physics 2. The experiment is about the title, a bar magnet being dropped through a solenoid. I have to explain four graphs that plot the change in emf (y axis) vs. time (x) axis. There are incoming and outgoing peaks on these graphs. I have to tie these results...

Hi everyone, This question is bothering me for days and would hope to receive some help in this forum. This question is with regards to Faraday's law on EMI. Will an emf be induced when a copper rod is accelerated between a uniform magnetic field? My answer would be no if the rod has...