Emf Definition and 939 Threads

Homework Statement hey! I saw you've answered this question before... Hi, I would appreciate any help with the following: The coil in a loudspeaker has an inductance of L = 112 microH. To produce a sound of frequency 40kHz, the current must oscillate between peak values of + and - 4.4 A in...

I apologize if this question is a bit confusing, but I am studying electrical engineering and what keeps baffling me is why when you run current through an inductor then place an open in the circuit how come the Back EMF current is able to cause a spark across the open. I get that the inductor...

Do electrons excite the EM field or do they just create virtual photons that do? If you could only see EMF excitations, would you see the electrons or virtual photons coming from the electrons?

From this diagram: If a conductor of length(##L##) is moving with a velocity(##v##) inside constant magnetic field(##B##), there is an induced EMF as indicated at the top of copper slab, and connected to a load and current will flow. I've been curious with the way the wires are connected to...

Homework Statement An electric motor draws 20.0 A of current when first switched on. The motors windings have a resistance of 5.0 ohm. Once the motor is up to full speed it draws only 4.4 A of current. Calculate the counter emf generated in the motor at full speed Homework Equations I = V/R...

Homework Statement Can somebody explain what ems is for a person (me) who has only heard of voltage? http://imgur.com/Y1JQy7w Lets say the batteries volt is 10V. Is it always going to be 10? Is the batteries ems 10V? Homework EquationsThe Attempt at a Solution

Faraday's law is $$\nabla \times \mathbf{E} = - \frac{d\mathbf{B}}{dt} $$ If we let our time dependent surface be ##\Sigma(t)## and its boundary ##\partial \Sigma(t)##, then by Stokes' theorem $$ \oint_{\partial \Sigma(t)} \mathbf{E} \cdot d\boldsymbol{\ell} = - \int_{\Sigma(t)} \frac{\partial...

Homework Statement Say we have a circuit where a cell with internal resistance r is connected to a voltmeter with extremely high resistance. This means practically all of the p.d would be across the voltmeter as the ratio of its resistance to the internal resistance is, say, infinitely high. So...

Hello Forum, the law of electromagnetic induction states that a time-changing current causes a back (counter) emf in an inductor. The back emf opposes the change in current by generating an induced current I_ind. If dI/dt>0, the induced current is opposite in direction to the main changing...

Homework Statement I'm answering a question which describes a situation in which a metal ring is dropped through a magnetic field such that, when it falls, its area is perpendicular to the magnetic field. I need to find its terminal velocity given: Mass : 2.66 x 10-4 kg Magnetic flux density ...

If you have a one solenoid inside another (with the same number of coils of wire) the current is going through the inner one. How does the induced EMF in the outer one depend on the frequency of AC in the inner one

Hey, I don't understand why emf generated is not the first derivative. For example I have a graph of magnetic flux through a wire against time. I thought that emf generated was the rate of change of flux, however this doesn't work. Emf=-Dflux/Dtime . In this example I have a y=sinx curve for...

I am having trouble with deducing the origin of Maxwell's Laws, especially Faraday's Law. Obviously some of the laws has to be originated by experiments and the rest should be mere deductions. I would guess that Lorentz force law is the empirical information where we just named some terms as...

Homework Statement In the circuit shown in the figure above, the ammeter reads 3.4 A and the voltmeter reads 6 V. Find the emf ɛ and the resistance R. Homework Equations Ohm's law; V= I*R EMF equations: ε=I*r+I*R ε=I*r+V The Attempt at a Solution [/B] I got the...

Hello, We know that the electric field generated by a changing magnetic field is not conservative. But, for example let' say we have an EMF source that has an internal resistor, the voltage drop across the source is equal to EMF-rI where r is the internal resistance. My question is, inside the...

I heard that, emf cannot be parallely connected provided that the value of the emf are not same. Is this correct? Like, what would happen when batteries with 3V, 4V, 5V are parallely connected? And the equivalent emf?

I am fixed to find out the reason what makes the charges get separated in conductor causing an emf leading to induced current. A very good reason exists for motional emf. It can be explained with the help of F=qvBsinΘ.

I'm trying to understand how electric generators work on a very basic level. I understand the heart of this is the application of the Lorentz force on a conductor moving at a velocity ##v## in the presence of a magnetic field ##B##. I also understand how it can be shown that the emf is equal to...

Homework Statement Calculate the total power generated by G Homework Equations P=VI The Attempt at a Solution I used the P=VI formula to calculate the total power generated by G which is 40W, and the answer turns out to be correct. But actually, I don't quite understand this topic of opposing...

Hi, A capacitor has both its terminals connected together using a wire in a rather lengthy circular fashion, hence acting as a significant inductance. If the area encircled by this 'circuit' is subjected to a linearly rising magnetic field (B=k x t) where k is a constant, the emf induced -due...

Here is a typical description of motional EMF: "The figure below shows a conducting rod of length L being moved with a velocity v in a uniform magnetic field B: The magnetic force acting on a free electron in the rod will be directed upwards. As a result, electrons will start to accumulate...

Hey guys been trying this question for a while now and i just can't seem to find any equations which link the two coils to find average EMF and also the final current I2. I am new to electrical so still learning any help is much appreciated, thanks! Two coils, A and B, are wound on the same...

Please tell me how use the symbol for the emf induced "E" in LaTeX. Thank you.

Assume we have the following copper slab, with volume ##V##, and introduced a magnetic field covering a small area of it like so: There is change in magnetic flux(##\phi##) due to the magnetic field increasing/decreasing, and via Faraday & Len'z law of electromagnetism, there is an induced...

I understand that EMF is generated by moving a closed loop of wire through a constant magnetic field. I am confused about one thing, who is actually doing work here? (of course it is not magnetic field).

Homework Statement A coil of insulated wire is wound many times around an iron bar. The wire is connected to a battery and a contact switch. The contact switch is alternately flipped closed and left closed, so the wire carries a current through it, and then flipped open and left open, so that...

If we have a conducting loop, and a magnet (say North pole first) is pushed into it; that induces and emf and hence a current in the coil due to the changing magnetic flux, right? According to Lenz' law, the direction of the current is such that it opposes the change. So from the side the magnet...

Homework Statement We conducted an investigation into wire length, current and resistance but kept track of the voltage rather than relying on the power pack setting. We noticed the voltmeter (measuring across the power pack) reading increased as the length of the wire increased though by only...

Homework Statement [/B] A conducting square frame of side a and a long straight wire carrying current I and located in the same plane as shown in the figure. The frame moves to the right with a constant velocity v. The emf induced in the frame will be proportional to Homework Equations [/B]...

I see a lot of problems on constant current inducing a current in another wire due to its associated magnetic field, but not so much a single wire's induced electric field. If the current along an infinitely long wire is flowing out of the page and inducing a counter-clockwise spinning magnetic...

Homework Statement There's a primary and secondary coil. The primary coil has 15 turns, and the secondary coil has 16000 loops. The 25000 V is applied to the primary coil, what will be the induced emf in the secondary coil. Homework EquationsThe Attempt at a Solution Very confused as to how...

Hey people I was wondering why is an emf induced in a loop which moves perpendicular to a uniform magnetic field. I mean, say the loop is a square of area r^2, and moves in the xy plane, where there is a uniform magnetic field B in the z direction. Why will an emf be induced? The flux remains...

I read the following statement in a book: "if polarity of m number of cells out of total n number of cells are connected in series with external resistance R is reversed then equivalent emf of such combination of cells is given by Eeq= (n-2m)E (where, each cell has same value of emf= E" I...

First this Q might be trivial thus apologies. Consider two bar electromagnets that can simulate bar magnets M1 and M2, placed end to end at distance D apart (North Pole of M1 facing South Pole of M2). Magnet M1 is 'fixed' to a base. Assuming both electromagnets have the Current I1 and Voltage...

Homework Statement u = velocity B = magnetic flux density Homework Equations ∫ (uxB)⋅dl The Attempt at a Solution From my understanding, the direction of dl depends on the resulting direction of (uxB). How will I know if my dl is in positive or negative?

Homework Statement A series dc motor:[/B] A dc motor with its rotor and field coils connected in series has an internal resistance of 2.00 Ω. When running at full load on a 120-V line, it draws a current of 4.00 A. a) What is the emf in the rotor? b) What is the power delivered to the motor...

Homework Statement A bar magnet is held stationary (with respect to the loop of wire) at the centre of the loop with the North pole sticking out one end and the South pole sticking out the other. What happens to the size of any EMF induced in the loop once the magnet has been replaced by a...

A 34 turn circular coil of wire has diameter 1.07 m. It is placed with its axis along the direction of the Earth's magnetic field of 60.0 µT, and then in 0.202 s it is flipped 180°. An average emf of what magnitude is generated in the coil? ε = − dΦB dt = −2Nπr 2B/dt = 16.95 when I used 3.14...

Homework Statement This isn't a homework problem per say but I am struggling with what we are doing in class at the moment which is to do with circuits with two sources of Emf. More specifically, how one source can be used to re-charge a battery. I have looked at the following website which i...

Hi everyone, I am currently stuck on this problem, and I was wondering if I could get assistance, at least in getting started. It'd be greatly appreciated!

Homework Statement A variable , opposite external potential ## E_{ext} ## is applied to the cell Zn | Zn2+ (1M) || Cu2+ (1M) | Cu, of potential 1.1V . When Eext < 1.1 V and Eext > 1.1V , respectively electrons flow from : 1. anode to cathode and cathode to anode 2. cathode to anode and anode to...

I have little problem in understanding emf in a circuit. There are three types of emf mentioned in textbooks and the first two are very similar: 1. The emf provided by a battery or other stationary power source. The emf is actually the voltage difference provided to the circuit. 2. The emf...

Homework Statement When a nonideal battery is connected to a 3.0-Ω resistor in a circuit, the current in the circuit is 2.0A . When the same battery is connected to a 1.0-Ω resistor in a circuit, the current in the circuit is 3.0 A. What is the internal resistance of the battery? What is the...

Homework Statement What is the magnitude of the magnetic field inside the solenoid at t = 1 ms? Homework Equations Not sure The Attempt at a Solution Well I would make an attempt but firstly I have a question. What I want to know is the above question simply referring to the emf of the...

Homework Statement Homework Equations Faraday's and Lenz' law. emf = -d(ф)/dt The Attempt at a Solution The current is increasing upwards during that time interval. Thus, by Right-Hand-Rule, the magnetic field goes into the page at the loop. Lenz' law says that the loop's induced emf...

I have been thinking about coils of wire carrying alternatingcurrent. From what I understand, a back emf is induced in the coil because there is a changing magnetic field around each individual loop of wire, and therefore there is a changing flux through each loop because the changing field...

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...