Emf Definition and 943 Threads

i have heard it said that back force occurs in generators and back emf occurs in motors, however I was considering a motor and I thought that it seems to me that as the coil is rotating and it has the changing flux linkage, and thus a back end is induced in it by Lenz's law, this reduces the...

Homework Statement A simple pendulum with bob of mass m and conducting wire of length L swings under gravity through an angle 2 theta. The Earth's magnetic field component in the direction perpendicular to swing is B. The maximum potential difference induced across the pendulum is Homework...

Homework Statement A square conducting loop lies in the xy plane of an xyz coordinate system. The loop is in a uniform magnetic field that points in the positive z direction and is decreasing at a rate of 0.070 T/s. What are (a) the magnitude of the induced EMF in the loop and (b) the direction...

Homework Statement It's Problem 6.6 on this page: http://web.ece.ucdavis.edu/~lxgliu/eec130a/2012winter/hw9s.pdf It has the solution and everything. I don't understand part (b) though. Homework EquationsThe Attempt at a Solution [/B] For part (b), I thought the direction of the induced...

A Power supply is connected to a parallel circuit with resistance R, there are three wires connected in parallel where the voltages would be the same,however, the current would be dived based on the number of wires and the resistance is the same. What would happen if wire (c) was placed in a...

I am having trouble understanding a process in the electric motor. using this website as a frame of reference (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/mothow.html), as an electric current is passed into that magnetic field, shouldn't the current also be creating a magnetic field, and...

1. A very large loop of metal wire with radius 1meter is driven with a linearly increasing current at a rate of 200amps/second . A very small metal wire loop with radius 5centimeter is positioned a small distance away with its center on the same axis (the loops are coaxial). The small loop...

Homework Statement [This is the best image I could find] The link on the bottom part of the rails is now removed creating two parallel wires that are not connected (so no longer U shaped but just two rails). Now a wire of length L, mass m and resistance R slides without friction down parallel...

Homework Statement A long, straight wire as shown below carries a constant current I. A metal bar with length L is moving at a constant velocity V as shown. Point ‘a’ is a distance ‘d’ from the wire. a) Derive an expression for the EMF induced in the bar. b) Which point ‘a’ or ‘b’ is at a...

Homework Statement Homework Equations For R, current I=E/R and for X, I=E/X... both are separate cases. The Attempt at a Solution [/B] Why does the balancing change? The potential difference across each resistor is E Itself right? I tried by assuming an arbitary internal resistance r...

A d.c circuit consists of a switch, lamp and inductor. The inductor is replaced with an inductor with twice the number of turns in the coil of wire, nothing else about it is changed. State the effect on A) maximum current B) the time to reach max current I thought increasing the turns would...

Hello, Does anyone shield themselves from computer / monitor from EMF radiation? if so what materials do you use to cover/coat your electronics? I am buying an EMF meter soon (Trifield 100XE) and plan on solving all my EMF issues, specifically around my computer tower, monitor, and other...

Homework Statement The coil in a loudspeaker has an inductance of L = 56uH (or 5.6 x 10^-5 H). To produce a sound frequency of 20 kHz, the current must oscillate between peak values of +2.2 A and -2.2 A in one half of a period. What average back emf is induced in the coil during this variation...

Homework Statement A simple electric generator contains a 30-turn coil of area 6.6 x 10^-4 meters squared. The coil spins in a magnetic field of 0.80 T at a frequency of 60 Hz. a) What is the peak output voltage? b) How must the number of turns be changed to maintain the same output voltage...

Something a bit boggling to think, which I accepted as a fact in nature, but might anyone explain as how is it possible to have to electromotive forces(EMF) at the same time in the same conductor? Assume a circuit placed in a magnetic field, that is connected to a voltage source(##\epsilon_1##)...

I have found an equation which gives the EMF generated in a coil when a magnet is spun near it, the equation is given as: E = FNAω × 10-8 volts. Where F is the field of the sample perpendicular to the axis of roation, N is the number of turns, A is the effective area of the coil and ω is the...

I was under the impression that an emf is the work done per charge by any source that is not electrostatic. However, there are such things such as emfs produced by varying magnetic fields. Being that magnetic fields never do work, what is an appropriate way of thinking of an emf?

Imagine a simple circuit, an EMF connected to a resistor which connects back to the EMF. This is how I'm thinking about it I know there is a current which means that there is charge moving around the loop which means that there must be some field because otherwise the charges wouldve never...

Homework Statement [/B] Suppose, there is a 'constant' magnetic field ##B## in the upward direction. A loop of conductive wire(XYZ in the picture, which is connected to a closed circuit with resistance R) is placed horizontally on it. The area of the loop is being increased with time. Will...

Suppose we have a closed circuit with a time-varying magnetic flux. An EMF is inducted on the circuit. Where would we put the battery representing the EMF? For example, suppose we have a resistance in the circuit and we want to know the intensity through it. Would we just set the voltage...

In the direct current circuit, when you have a switch and you turn it on, you get the coil to generate a current to the opposite direction but the magnitude isn't big enough to offset the main one. But in the case of alternating currents, the coil seems to generate enough current up to the...

I should add context to this question that what I know so far of the emf is that it is defined as ##\mathscr E=\oint f \cdot d\ell## where ##f## is the sum of the forces on the charges. In the textbook I'm reading it gives an example of where a person pulls a rectangular wire with a velocity...

i am having some trouble with understanding the magnetic fields inside transformers and how they relate to back emf. In particular, I am considering the two cases of current passing through the primary coil but not the secondary coil, and then with the secondary coil as part of a complete...

Homework Statement So this is not really a 'solve this problem' question, but, rather, I am trying to understand how they can call ABCDEFA a 'closed loop' even though there is another connection (BE) inside it, and why the equations work. Keeping in mind that I am still in high school...

Faradays law tells us that a change in flux induces an emf. Now consider the phenomenon of motional emf. It is observed across the ends of an open conductor (ie one which is not in a circuit). It is always discussed in connection to faradays law. Where is the change in flux in the case of a...

It's kind of embarassing but I have almost finished a introductory EM class and I'm still not sure in a formal way in which cases the EMF is equal to the voltage. EMF was defined as the work done on a charge per unit of charge by any EM originated force when the charge would take a certain path...

Homework Statement Uploaded the question below , Part B Homework Equations Φ=NBA EMF= (delta)Φ/(delta)t V=IR The Attempt at a Solution so i found the area (0.25x0.3) and then divided by two (=0.0375m^2) , then found Φ=80x1.4x0.0375=4.2wb However , in the marking scheme they multiplayed by...

is "motional emf "the real explanation for the reason why emf is induced in faraday law?? thanks...

For motional EMF: $$ \epsilon = -vBL$$ If a conductor moves in a constant magnetic field, there isn't induced EMF correct? Only when existing/entering the field there is induced EMF? I've had this misconception, that any motion(fast/slow) in a magnetic field would instantly induced EMF, but I...

Homework Statement Students are given some resistors, a battery with internal resistance, and an ammeter. They are asked to determine the emf e and internal resistance of the battery using just this equipment. Working with the circuit shown at right, they insert each resistor into the circuit...

I have been studying electromagnetism this year and we have spoken about Faradays law of electromagnetic induction and eventually how the emf induced is equal to the negative time rate of change of magnetic flux I noticed however that all examples include a time varying magnetic field, which...

Does an emf create across the body of a magnet when the magnet is linearly moving across its own field. If ABCD is a rectangular magnet of thickness t, AB is the north pole and CD is the south pole. If the magnet moves in the direction of t, that is perpendicular to ABCD plane, will there be an...

to calculate emf i can use the flux rule -d(magnetic flux)/dt or the lorentz force line integral across the circuit. Is there a gudeline to follow for knowing when to use either (or both) of these methods? Thanks :D

The n = 2 energy level of lithium is 108.8 eV away from the n = 1 energy level. Does that mean, in a DC circuit, that if you put an emf of 108.8 V along a lithium wire, that the high voltage will excite an electron to the n = 2 level?

I know this may seem a silly question, but i can't find the answer in searches, if 2 emf waves travel at the speed of light in a vacuum and one is a gamma ray and the other a radio wave which one would travel from point a to point b faster? if a radio wave is the size of a building and a gamma...

Homework Statement two 8 ohm resistors and a battery of emf 12.0V and internal resistance of 8ohms are connected in series. Calculate the power delivered to each external resistor and then calculate the power wasted due to internal resistance. I keep coming up with the answer 18 but apparently...

Homework Statement Consider the loop in the figure below. What is the maximum induced emf in each of the following cases if A = 600 cm2, ω = 31.0 rad/s, and B = 0.490 T? Rotating about x,y,z? Homework Equations Faraday's law The Attempt at a Solution This should be relatively easy since the...

Homework Statement The current in a solenoid (you may treat it as a long solenoid of length 2.0 m, turns, and radius 0.5 m) is decreasing at a rate of 1.7 A/s. What is the EMF at a point .35m inside the solenoid? Homework Equations B=N(mu_0*I)/(2a) where B=magnetic field, N=turns per...

Hello all! I'm confused about an explanation that my textbook gives, and I'm wondering if someone can help me understand it. The passage is as follows: A circuit consists of a 12 V battery with negligible internal resistance, in parallel with a charging unit with an emf of 15 V and internal...

why does induced emf change in case of generators but remains constant in case of moving conductor?

Homework Statement A rectangular loop of wire, of sides 5 and 3 cm moves away from a a long straight wire at 4ms-1 carrying a current of 2 amps. What is the EMF induced in the moving loop, when the near side of the loop is 3cm away from the wire? Homework Equations B = μ0I/2πr EMF = -dΦ/dt...

I measure the Electromagnetic Field Radiation at a point for example x distance from a source, and i am reading for ex. 15 milli volts per meter. Are these 15 millivolts per meter, equals to 15 milli volts ? I mean, if i do the opposite procedure, and receive a reading of 15 milli volts, at a...

The potential difference between the ends of a wire is given by Vab = IR. Combing that with E = Vab we have E = Vab = IR (ideal source of emf). " That is, when a positive charge flows around the circuit, the potential rise as it passes through the ideal source is numerically equal to the...

Homework Statement The title. I am confused with the definition as my textbook does not have a good definition for this. P.S I have my exams tomorrow so I can't ask my teacher now.(Mid night) Homework Equations $$V=\frac{E}{Q}$$The Attempt at a Solution E.M.F is the energy given to each...

Motional EMF is defined as E = -vBL Where B is the magnetic field in Tesla, L is the length in meters and ,v is the velocity. Lets say we have a distance(1m) where half of it(0.5m)the magnetic field is present. So, there is a wire that moves with constant acceleration throughout that whole...

Hi pf, I have been reading about back EMF and just had a few questions. I found this article on wiki (http://en.wikipedia.org/wiki/Counter-electromotive_force) and the last paragraph talks about the effects of back emf when you plug a vacuum cleaner into your wall. It says that you can notice an...

Hello all. I am currently studying electromagnetism with Griffiths' books, and I have already donde electrostatic and magnetostatics. Now I am reviewing Ohm's law en emf concepts, but I have a doubt: In griffths book, when explaining ohm's law and emf, it seems to me that he assumes...

Hello everybody, I am trying to figure out how to build an electro magnetic generator. I was wondering if an audio transducer such a speaker could act as a EMF generator, when the paper woofer is removed and the device connected to a function generator and an amplifier, in order to play the...

Hello everybody, I am trying to figure out how to build an electro magnetic generator in order to stimulate my home and my brain with beneficial frequencies such as the Schumann resonance and doing perceptive experiments on all the surrounding frequencies. I was wondering if an audio transducer...

Homework Statement A loop of wire with an area 1cm^2 is centered within a larger loop of area 1m^2. Apower supply is generating current through the larger loop described by the function: I(t) = 40A * cos(2t/s * 2pi/5) Calculate EMF at time t = 3sHomework Equations Magnetic flux =...