Emf Definition and 939 Threads

i know an emf device maintains a potential difference across a circuit. it does so by doing work on charge Carriers. this means it somehow maintains a force in the circuit. I also know there are two terminals present in an EMF device. are these terminals charged so as to maintain an...

Homework Statement Griffith ( Introduction to electrodynamics , 3 ed.) says in Problem 7.9: An infinite number of different surfaces can be fit to a given boundary line, and yet, in defining the magnetic flux through a loop, Φ = ∫B.da, I never specified the particular surface to be used...

There is magnetic field in B = B ##\hat z## in a region from x=0 to x=l. There is a metal rectangular wire loop with length l and width w in x- y plane with coordinates of four corners as (0,0),(0,w),(l,0),(l,w). This loop is moved with velocity v=v##\hat x##. Now according to Faraday's law...

Homework Statement Homework EquationsThe Attempt at a Solution I got a Magnetic field by "Magnetized needle". I think it's just magnet. But i don't know how to get a magnetic flux due to the variable "d" that should be erased.

Exercise: I'm suppose to prove that e1 = e2 e1 = ∫E*dl e2 = ∫dB/dt*dS where S is the surface encircled by the conture c. c is a box with with a length (in x axis) and b height (in y axis). for an electromagnetic wave: E = E0*sin(kx - wt) (in y axis) I'm ASSUMING this means that B =...

Is the work done by a constant voltage source positive or negative when current is opposite to emf?

While the motor is spinning, I measured the voltage (Vrm) across the motor by connecting the two probes from the multimeter to the two terminals of the DC motor via alligator to alligator banana cables. Since the current was fairly constant, I could ignore the inductance. So, no voltage across...

Homework Statement Homework Equations L = (N * F_b) / I (where F_b is the magnetic flux) emf = -L * (dI/dt) The Attempt at a Solution I originally thought that the inductance would decrease since it is inversely proportional to current. But, looking at the equation for emf, that would...

Hello all - I've stumbled upon what seems to be a pretty basic magnetic materials question that's got me stumped. Maybe one of you can help me figure this out. I did the following experiment (see figure below): Put a ferrite toroid around a current carrying wire carrying 12 Amps RMS at 120V...

Homework Statement Homework Equations induced emf = - d(magnetic flux)/dt The Attempt at a Solution [/B] I believe the graph will start initially curving upwards, because it begins to cut more and more flux lines which lead to an increased induced emf. Once it is "fully" within the...

Homework Statement When an external resistor of resistance R 1 = 14 Ω is connected to the terminals of a battery, a current of 6.0 A flows through the resistor. When an external resistor of resistance R2 = 64.4 Ω is connected instead, the current is 2.0 A. Calculate the emf and the internal...

Homework Statement A coil with 200 turns of wire is wrapped on an 18.0 cm square frame. Each turn has the same area, equal to that of the frame, and the total resistance of the coil is 2.0Ω . A uniform magnetic field is applied perpendicularly to the plane of the coil. If the field changes...

Homework Statement The region is a circle with radius=a Homework Equations Using Faraday's law to find E. The Attempt at a Solution Dealing with the Left side of the second equation first 1.) Pull out the Partial/partial t because it is a constant in this equation 2.) Now I have B dot...

Hello Physics Forums users, Thank you for taking the time to read my thread. I has just reading through this following article: http://www.sciencehq.com/physics/electromagnetic-induction.html when I came across this: And became rather confused. The right hand rule dictates that in this...

Homework Statement A small coil of wire is situated in a non-uniform magnetic field. The coil consists of 40 turns of wire and moves with a constant speed in a straight line. The coil has displacement x from a fixed point P. The variation with x of the magnetic flux in the coil is shown in the...

As the title states, can EMF = I = const ?

Homework Statement I need to calculate EMF and internal resistance from the given resistance and voltage. R = 3 ohms U = 3,6 V EMF- ? I0 - ? r - ? Homework Equations I = U/R EMF = A/q I = EMF/R+r I0 = EMF/r The Attempt at a Solution I = 3,6/3 = 1,2 A I = EMF/R+r 1,2= EMF/3+r ^ I hit a wall...

Hello. Let's say a current i(t) flows through an inductor of solenoid type. Time-varying i(t) generates a magnetic field B(t) inside the magnetic core of the inductor. As B(t) is time-varying, EMF, which is the line-integral of the induced electric field E(t) along a coil (which carries i(t))...

Homework Statement A generator consists of 500 turns each of surface area 7/11 m² . It rotates at rate of 50 revolutions per second (f =50 Hz), in a field of magnetic flux density of 5*10^-4 T, its terminals were connected in series with a capacitor (Xc=110Ω), an inductor (Xl=80Ω) and a...

Homework Statement See image below. Homework Equations motional emf = induced voltage = B L v The Attempt at a Solution I thought the answer would be A since there's a direct relationship between EMF and magnetic field strength. The answer is D.

Hello, I got two series connected coils which I exited with 15 V AC. I got EMF between the space in the field and I measured it with gaussmeter saying 200 µT. I want to know the freqency of that generated electromagnetic field? Does anyone know how to do it? Is there any Equation for it...

Homework Statement In a circuit of constant current shown in the image, values are Ig=0.2 A AND R=750 ohm. What is the value of EMS of an ideal voltage source V for the powers of an ideal voltage and an ideal current source to be equal? Homework Equations Pv=PIg The Attempt at a Solution I...

Hi, Consider a wire with a pulsating DC current next to another wire. The expanding and contraction magnetic field induces a current into the second wire. Consider the same but in the second case we have a metal chassis. I assume the same magnetic field is inducing a current into the chassis...

Homework Statement My problem is trying to understand this graph and explain why it changes the way it does Homework Equations [/B] e=change in ∅/change in time The Attempt at a Solution [/B] I know that the magnetic field increases/decreases when the magnet is on the way into the coil and...

In Purcell- Electricty and Magnetism book, in the chapter on electromagnetic induction, I found the following explanation regarding the magnetic flux through a circuit of area ##S##. Consider the circuit in figure, moving in a time ##dt## in a magnetic field ##B##, constant in time (but not...

I would really appreciate some clarification about how to draw graphs showing changing flux and induced EMF. I understand that there needs to be a 90 degree phase difference as the EMF is a maximum when the flux has the greatest rate of change. However, our exam board says that the EMF can be...

Homework Statement The following circuit is given. I intend to calculate the current in every resistor (every quantity except i1, i2, i3, is known). My textbook states that ℰ3-ℰ1 = (R1+R2+R3+R4+2r)*i, but I think it should be -ℰ3+ℰ1 on the left-hand side, since the current enters the negative...

The induced emf in a straight wire is determined by the equation (emf=Blv sinθ) where θ is the angle between the direction of the motion and the lines of the magnetic field, and frequently, I see diagrams like these explaining the phenomenon: In those pictures the wire is perpendicular to the...

Homework Statement Explain what happens in the following situation: You have a loop in the form of a circle and there is a varying magnetic field inside that loop as the following picture illustrates: Homework Equations Faraday's law lorentez force The Attempt at a Solution I first thought...

I just read in my textbook that it is impossible to harness electricity from the induced emf if the velocity of a conductor is parallel to its straight length. Let me elucidate further: a magnetic field goes into the page and a straight conductor is moved straight down or up (perpendicular to...

Hi everybody, I have an oscillating circuit that consist of a charged capacitor and two conductors connected that can be seen as the inductance. When I short the conductors at their ends an oscillation can be seen on the oscilloscope. When I put an iron tube around each of the wires the damping...

Homework Statement Homework Equations Kirchhoff;s first and second law, V=IR The Attempt at a Solution Tried the question as follows: V= 24/(2+6+4) = 24/12 = 2V (pd from top cell) then did 2=4 I3 therefore I3 = 0.5A and then 2 = 6I2 I2 = 0.33A and I1 = 0.5+0.33... =0.83A?

I have been searching for ways to calculate resonance frequencies of complex molecules. I know that doing so is extremely complex, especially if that molecule contains many elements, but perhaps it could be feasible to target a specific component of a large molecule, such as a nucleus in a cell...

When I induce magnetic flux through a closed loop, I should expect the lines of flux produced by current in that loop to oppose the change of flux through that loop. But what happens when that loop, say a rectangular loop, is curved into the shape of the letter J (like a candy cane) and my flux...

Homework Statement An A/C starter has a 12V supply & a back EMF of 6V. If the resistance is 0.1 ohms, calculate current during start-up & while in operation Homework Equations E=IR Not sure what else? Sorry I am stuck. The Attempt at a Solution Start up current E=IR 12V=I x .01 I = 120A...

Homework Statement Two concentric circular coils of wire lie in a plane. The larger coil has 61 turns and a radius of a = 7.40 cm. The smaller coil has 58 turns and a radius of b = 0.95 cm. The current in the larger coil has a time dependence as shown in the figure. Picture and graph...

Does a conductor from space to Earth mess with the separation of charges in the solar system?

I'm currently in conceptual phase of designing a coil gun. Thinking back to my physics 2 class-- and some of my independent studies-- I understand an EMF produced by a solenoid with current through the wires of it is strengthened significantly by a ferrous core, as seen by the classic experiment...

Homework Statement So I'm trying to figure out this problem: The base of our charging station is composed of a coil with N1 turns and area A1 connected to a 120 VAC, 60 Hz source. The device has a smaller coil with N2 turns and area A2, which when attached will fit completely inside the...

Hi, I was doing an experiment with Neodymium magnets and a long copper pipe (3cm internal diameter) to see Lenz's Law in action. At first I used a long bar magnet (about 15cm long) and there was little resistance to the magnet falling through the pipe. It was only slightly slower than a...

Homework Statement A copper disc of radius 10 cm is situated in a uniform field of magnetic flux density 1.0 * 10-2 T with its plane perpendicular to the field. The disc is rotated about an axis through its centre parallel to the field at 3.0 * 103 rev min-1. Calculate the EMF between the rim...

What is emf in the coil? As far as I know about emf is that it is potential difference between two terminals of a source but what if it is induced in coil by changing flux linkage. What exactly happen when emf is induced?

Homework Statement A bulb is used in a torch which is powered by two identical cells in series each of EMF 1.5 V. The bulb then dissipates power at the rate of 625 mW and the PD across the bulb is 2.5 V. Calculate (i) the internal reistance of each cell and (ii) the energy dissipated in each...

Homework Statement (a) In the circuit shown below E is a cell of source (internal) resistance r and the resistance of R is 4.0 Ω. With the switch S open, the high resistance voltmeter reads 10.0 V and with S closed the voltmeter reads 8.0 V. Show that r = 1.0 Ω. (b) If R were replaced by a...

Homework Statement A battery of EMF 12.6 V and internal resistance 0.1 Ω is being charged from a DC source of EMF 24.0 V and internal resistance 1.0 Ω using the circuit shown in the figure below. V1 and V2 are high resistance voltmeters and R is a fixed resistor. (a) What is the polarity of...

Homework Statement The battery in the circuit below has EMF 5.4 V and drives a current of 0.30 A through a lamp. The voltmeter reading is 4.8 V. Explain why the voltmeter reading is less than the EMF of the cell. Calculate values for (a) the internal resistance of the battery, and (b) the...

Homework Statement A battery is known to have an EMF of 5.0 V but when a certain voltmeter is connected to it the reading is 4.9 V. The battery can deliver a current of 0.40 A when connected to a resistance of 12 Ω. What is the resistance of the voltmeter? Answer: 24.5 Ω. 2. The attempt at a...

Homework Statement A power supply used in a laboratory has an EMF of 5000 V. When, however, a voltmeter of resistance 20 kΩ is connected to the terminal of the power supply a reading of only 40 V is obtained. (a) Explain this observation. (b) Calculate (i) the current flowing in the meter and...

Homework Statement Explain why the PD between the terminals of a cell is not always the same as its EMF. A cell, a resistor and an ammeter of negligible resistance are connected in series and a current of 0.80 A is observed to flow when the resistor has a value of 2.00 Ω. When a resistor of...

Homework Statement The figure below shows a closed loop of wire that consists of a pair of equal semicircles, of radius 7.0 cm, lying in mutually perpendicular planes. The loop was formed by folding a flat circular loop along a diameter until the two halves became perpendicular to each other...