Emf Definition and 902 Threads

Hi all, I've been using Faraday's law to find the EMF in a coil of wire in a changing magnetic field. EMF = -N (change in mag flux/change in time) for N loops I'm finding that the EMF is always positive regardless of whether the change in flux is positive or negative. I'm wondering at...

Homework Statement In the figure below, a circular loop of wire 12 cm in diameter (seen edge on) is placed with its normal at an angle θ = 30° with the direction of a uniform magnetic field B of magnitude 0.60 T. The loop is then rotated so that N rotates in a cone about the field direction...

Homework Statement A square wire loop of dimensions L X L (L = 15.5 cm) oriented in the xy-plane and centered on the x-axis enters a region where the magnetic field (B = 0.855 T) is first oriented in the +z- and then in the -z-direction as shown in the diagram below. (Note: W = 15.501 cm and...

what is the Effective emf of 2 cells with zero internal resistance connected in parallel (E1>E2)

According to Faraday's laws... change in magnetic flux linking a coil induces current in the coil.., but for conduction of electrons ...there must be an electric field ! how is the electric field induced in the coil??

Homework Statement "You push a rectangular loop of width .2m, length .8 m, and resistance R=200\Omega into a magnetic field (out of page) Bout=.4 T and a speed v=.2 m/s. The long side of the rectangle is parallel to the x axis. What is the current flowing in the loop?" Homework Equations I...

I've been going through some materials, and I was reading about electric circuits. From what I read I figured that the electric current is dictated by the current source, and it's preserved(in the respectable branches) by the emf. Is that right? Or my feeling that I'm way off is true :)

Homework Statement Find the induced emf in a rotating disc of radius (a) in a magnetic field (B), rotating with uniform angular velocity (w). If the disc is replaced by a rotating conductor of length (a) fixed at one end find the induced emf in the conductor. 2. The attempt at a solution...

Hi I have a practical problem/question: I need to wire 2 PLC-s for communications (RS485 signal) and I am planning to use shielded twisted pair cable (Cat5 FTP). The signal cables are quite short - approx. 6 m. One possible problem that could arise: between the 2 PLC-s, there is a...

Homework Statement A circular coil of area A with N turns rotates at an angular velocity w about an axis perpendicular to its own axis and to a uniform magnetic field B. Find an expression for the induced EMF in the coil in terms of B, N, A, w and time t. What is the orientation of the coil...

I know the equation for emf: -dflux/dt= -dB/dt*A . In my case everything is constant accept the magnetic field and I am unable to find the equation for that. I know that is what dB is for but that simply does not work in this case. What is the equation for induced voltage, when everything is...

Homework Statement Consider a circular loop with resistance R. Perpendicular to the loop there is a magnetic field B(t) = t, where t is the time. If a voltmeter is connected to two points on the loop separated by 90 degrees, what would it show? The Attempt at a Solution the answer...

Homework Statement What is the emf E of the battery at the lower left in the figure? Answer in units of V. http://img508.imageshack.us/img508/6/82852928.png Can someone guide me? I'm confused as to where to start. I think I am supposed go the route of the loop, but I am given the...

Homework Statement A wire of resistance 11 ohms and length 2.3 m is bent into a circle and is concentric with a solenoid in which the magnetic flux changes from 8 T·m2 to 6 T·m2 in 0.2 seconds. a) What is the emf in the wire? b) What is the non-Coulomb electric field in the wire? c)...

i am wondering why in some problem they are regarding back emf of a motor as a constant value that characterizes the motor although current is sometimes variable? i guess the reason is for simplifying the problem, what do u think? can this occur in reality? thanks for helping.

Sorry, the title is wrong. Should be "magnetic flux" of a single loop wire around a solenoid. Homework Statement A solenoid 4 cm in diameter and 20 cm in length has 250 turns and carries a current of 15 A. It is surrounded by a loop of wire 10 cm in diameter. The loop is positioned...

while solving an exercise, i have found that they are considering the back emf of a motor constant although the current is not constant? how comes that? shouldn't it be variable as current varies? they are considering that as E=Ir+E' where E' and r are constants?

Homework Statement determine the terminal voltage in each battery. Emf1=18V r1=1 ohm EMF2=12V r2=2 ohm R=6.6 ohms also the batterys currents are opposing each other. Homework Equations Vab=emf-Ir The Attempt at a Solution i used kirchnoffs rule to find the current I ...

Homework Statement http://img854.imageshack.us/img854/3980/33288207.th.png Uploaded with ImageShack.us The Attempt at a Solution http://img813.imageshack.us/img813/1065/60582408.th.png Uploaded with ImageShack.us \varepsilon = IR \varepsilon = -\frac{d \Phi}{dt}...

Homework Statement Why is the following situation impossible? A battery has an emf of E = 9.2V and an internal resistance of r = 1.2 ohms. A resistance R is connected across the battery and extracts from it a power of P = 21.2W. Homework Equations My book gives these equations throughout the...

Homework Statement Hey guys, This is just a qualitative question. So assume I have a massive super large magnetic field, and pull a straight, isolated conducting wire sideways through it with constant velocity. I know that the EMF induced is given by emf = Blv where l is the length of the...

1-this is what is written in my book: E= Ir+E' where E' is the back emf, r and E' are constants P(mechanical)=E'*I an electrical motor functions only if the generator connected across its terminals delivers a positive potential difference that exceeds its back emf. So my question is, why are...

1. In the figure the square loop of wire has sides of length 2 cm. A magnetic field points out of the page; its magnitude is given by B = 4.0 t^2y where B is in teslas, t is in seconds and y is in meters. Determine the emf around the square at t = 1.50 s...

Hey Folks. I am currently designing a buggy which tracks an inductive wire using two inductor sensors. The wire is carrying 20Vac pk-pk , 125ma at 10kHz. I have designed a sensor circuit which has a ratio of 2:1 ie it outputs a waveform of 10Vac pk-pk (assuming 100% mutual inductance). This is...

I don't know English well(I'm from russian speaking countries) but I try to explain the problem(and practise my english too) Homework Statement Transfrom scheme into eq. scheme with one EMF and one resistor. Homework Equations Where is the series configuration of resistors and where is...

Homework Statement A cell is connected to a 10.0 Ohm resistor. The pd across the 10.0 Ohm resistor is 10.43 V. A 4.00 Ohm resistor is connected in parallel with the 10.0 Ohm resistor. The pd across the 10.0 Ohm resistor falls to 7.87 V. Calculate the emf and the internal resistance of the...

Homework Statement A conducting loop is made in the form of two squares of sides s1 = 3.8cm and s2 = 6 cm as shown. At time t = 0, the loop enters a region of length L = 18.6 cm that contains a uniform magnetic field B = 1.2 T, directed in the positive z-direction. The loop continues through...

Homework Statement A 1.2 kg rod that has a length of 1m and a resistance of 5 ohms slides with constant speed down a pair of frictionless vertical conducting rails that are joined at the bottom. Other than the rod, the rest of the circuit is resistance-less. A uniform magnetic field of...

The title says it all. Please be detailed, the question is 6 marks. Thanks.

Homework Statement In the circuit (http://i.imgur.com/II38M.jpg),a variable resistor R is connected across the terminals of a battery, and an ideal ammeter and ideal voltmeter are also connected. In the figure, E is the internal emf of the battery, and r is its internal resistance. All the...

Hi all, I have a certain problem I'm getting stuck on hopefully someone here can help Homework Statement A rectangular coil is 75 mm wide in the y-axis, 100mm long in the x-axis. What is the speed of the rotation if an rms voltage of 0,25 V is developed in the uniform field of B =...

Why the back emf of the primary coil always equal to the supply voltage but no greater than supply voltage(because of the large number of coil turns) when no loaded?Or it is a kind of dynamic equilibrium?If yes,how it reach equilibrium? Thank you.

A Rectangular wire frame, is placed in a uniform magnetic field directed upward and normal to the screen. A side AB is connected to the spring . The spring is stretched and released when the part has come to a point A'B'(t=0). How would the induced emf vary with time? - Graph & Equation...

According to the faraday's law,the induced emf is proportional to the magnetic flux change linking the conductor.However,I wonder why there is induced emf when conductor is moving in uniform magnetic field,because i think that the magnetic flux linking to it is always the same as it move in...

Homework Statement When a 60 \Omega resistor and a 120 \Omega are connected in parallel across a battery there is a current of 700 mA flowing through the battery. When the 120 Ohms resistor is disconnected from the circuit the current through the battery drops to 500 mA. What is the emf and the...

Homework Statement I just took a test, and I am very unsure of the validity of how I approached the problem. Just looking for some feedback cause this is bugging me! There is a circuit in the xz-plane (vertical), and the circuit has on it a gate. The gate is a pendulum of length L, which...

I had already posted this question in the homework category but since i did not get any replies i thought maybe i should post it here again... A U shaped conducting tube is placed in a constant magnetic field in the downward direction. On the left of the tube is a resistance R.All other rods...

Dear Friends, Well is EMF both conservative and non conservative at the same time, or is it simply a paradox.I have written a small article on it proving it's conservative and non conservative nature... read it @: http://laps-of-mind.blogspot.com/2011/02/truth-about-emf.html" well I need...

Faraday's law says that an induced voltage across a conductor is directly proportional to the rate of change of magnetic flux through the conductor, but I am having trouble getting my head round how it works in this situation. Imagine a perfectly circular thin copper disc, and that this disc...

'it is emf when no current is flowing outside the cell. Whereas, it is potential difference is when current actually flows out of the cell." "that emf is the potential difference when there is no current flowing through the circuit or when the key is open. Whereas, the circuit has certain...

Hello. One doubt. How is the distance between the charged particles and the EMF between them get balanced out? That is, if I have a proton and electron, they attract each other, move towards each other and form a H atom. But going by this attractive force, they should approach each other...

Hello. > Is there any electromagnetic force of repulsion between two quarks? > And, hypothetically speaking [as independent quarks are not observable], could there be EMF of attraction between an electron and an independent quark? Actually, both the questions boil down to the following -...

I read this topic in many books but i really can't figure out what really the difference is! Please someone help me out! One of the book differentiated them as follows ... emf is the work done by the battery force (Fb) in moving unit charge from one electrode to another. emf is due...

Homework Statement This problem arises from a much larger essay/lab/project thing. I know that there is an induced current in the wire of an AC electromagnet because the magnetic field is constantly changing along with the AC current, so it makes sense to me that will produce a constantly...

Hey, I'm trying to find a suitable diode to protect against some back EMF in my circuit, but I don't know much about them and so I'm having a really hard time finding one. If someone could look at what i need and then possibly send me a link i'd be so grateful. Requirements: back EMF = 137mV...

Homework Statement A square loop of side .45 m is placed in a region where there is a magnetic field of strength 8T directed perpendicularly out of the plane of the loop. If the magnetic field is increased to 14 T in .03 seconds, calculate the average emf induced in the loop Homework...

Suppose now i have connected a solenoid with a dc power supply of 10V When i increase the voltage to 20V the magnetic flux through the coil have increased will emf be induced shortly to oppose the change? what if i now change it to a 10V ac power supply so will there always be induced emf...

If the Earth's magnetic field as measured on the surface of the Earth is somewhere between .3 and .6G and cell phone doses are around 2mG, is it then absurd to be at all concerned with even heavy exposures to the kind of low grade doses that cell phones and other electrical devices produce? I...

Hi. Could you please give me a description/analyse a variety of flux changes that can be used to produce an emf. Could you confirm what is flux and emf in this situation?

Homework Statement A bar of mass m, length d, and resistance R slides without friction in a horizontal plane, moving on parallel rails. A battery that maintains a constant emf \epsilon is connected between the rails, and a constant magnetic field B is directed perpendicularly to the plane...