Emf Definition and 939 Threads

Hai - I am revising and now I am confused - equations for both electromotive force (emf) and energy begin E=... (in different sections of my electricity notes) Does that mean EMF is a type of energy or am I missing something? Thanks :)

Homework Statement A current of 22 amperes flows in a heater coil whose resistance is 5 ohms. What E M F in volts is required? Homework Equations The Attempt at a Solution Not quite sure where to begin. I'm thinking the internal resistance, R, is inherent w/the circuit so EMF...

Picture link: http://es.tinypic.com/r/5cx154/5 A square loop of wire measures 2.00 cm on each side. It is attached to a cart that is moving at a constant speed of 15.0 m/s into a uniform magnetic field of 56.0 T. (a) What is the induced emf after it has traveled 1.00 cm into the field? (b)...

Homework Statement A coil is wrapped with 247 turns of wire on the perimeter of a square frame of sides 27.3 cm. Each turn has the same area, equal to that of the frame, and the total resistance of the coil is 2.53. A uniform magnetic field is turnedon perpendicular to the plane of the coil...

Homework Statement Thermal energy is to be generated in a 0.31 resistor at the rate of 11 W by connecting the resistor to a battery whose emf is 2.1 V. (a) What potential difference must exist across the resistor? (b) What must be the internal resistance of the battery...

ok, if i have a rectangular loop parallel to the screen and in a uniform constant magnetic field pointing perpendicularly outwards of the screen, if i move the loop to the right of the screen, will there be an induced emf in the loop? my understanding is that there will be? because we have a...

Homework Statement A coil with 253 turns of wire, a total resistance of 28 Ohms, and a cross-section area of 0.36m^2 is positioned in a plane perpendicular to the field of a powerful electromagnet. What average current is induced in the coil during the 0.33s that the magnetic field drops...

Ok... so there really isn't a homework problem that goes directly with what I am asking... I just want to understand how/why induction (magnet through a coil) gave certain results in our Science Workshop program... Here is what we did in our lab: We dropped a magnet (south end in first)...

Homework Statement If R1 = 4 x R2 then what are the values of the potential difference in terms of the EMF, E? I have R1 = 3/4, and R2 = 1/4 but that seems a bit simplistic, then I tried plugging it into equations and got completely different answers. Homework Equations R=V/I (?)...

The Earth’s magnetic field at a certain location in the UK has a magnitude of 48 μT and is directed at 66° below the horizontal. a)Determine the magnitude of the flux of the Earth’s magnetic field through a wedding ring of diameter 2.2 cm when the ring is held in a horizontal plane...

1. Homework Statement : A circular loop of flexible iron wire has an initial circumference of 166cm , but its circumference is decreasing at a constant rate of 13.0cm/s due to a tangential pull on the wire. The loop is in a constant uniform magnetic field of magnitude 1.00 T, which is oriented...

I searched practically all of the nets and webs and still my questions are unanswered, so I decided to consult y'all. I have previously asked you guys about diode sizing to prevent back emf on a relay and you were very helpful. I am once again calling upon your help. I have some relays in my...

Homework Statement A circuit consists of three fixed sides shaped like a |_| and a sliding rod of length 2R. The rod slides at constant speed v into a region of nonzero field B coming perpendicularly out of the paper and limited to a circle of diameter 2R. What is the magnitude and sense...

Homework Statement The area of a 100 turn coil oriented with its plane perpendicular to a 0.28 T magnetic field is 4.3×10−2 m^2. Find the average induced emf in this coil if the magnetic field reverses its direction in 0.36 s. Homework Equations E = -N (flux - flux initial)/(t-to)...

Suppose I have a conducting bar moving over a constant magnetic field. A Lorentz force arises on the charges that constitute the bar, polarizing the bar, and generating what is called motional emf. How can I explain this from the bar's point of view? From its own reference frame, the bar is...

Hi Experts,o:) I am trying to reverse the direction of a spinning dc motor (around 30watts) but not sure how this should be done. I have a logic for the switching of the power polarity to the motor but am worried if back emf would be an issue when the motor is spinning and the polarity...

Homework Statement The setup is a pair of two circular wires, a small one of radius b and a large one with radius 2b, both sharing the same center and located on the same plane. There is a magnetic field of strength B within the smaller circle that comes out of the paper towards the observer...

Homework Statement A square loop of mass m resistance R and side l] is halfway inside a magnetic field pointing into the page. It is then released from rest and gravity pulls it out of the magnetic field. a) Calculate the induced emf and the current as functions of the velocity. b) Calculate...

Homework Statement Use the law of electromagnetic induction to deduce what typical voltage would be imposed in the magnetopause by the interplanetary magnetic field, assuming a scale size of the magnetopause of 10Re? Homework Equations -Magnetic flux equation -Faraday's law...

Hey guys. I was reading http://kansascity.injuryboard.com/automobile-accidents/toyota-recall-experts-point-to-electronics-electromagnetic-interference.aspx?googleid=277752". This paragraph jumped off the page to me, and I wanted to get your thoughts on how feasible it it. To me, it reads like...

Homework Statement Describe the way that the loop is facing for this value to be a maximum. What is the equation for the emf for the rotating loop? Homework Equations I don't know. The Attempt at a Solution I can't really attempt the problem without the equation. This is a...

Are these things for real? I know that most of the crystal pendant crap is fake, but what about teslar watches? Are there actual wristband/necklaces that can cancel, or shield a body from EMF? Thanks.

Can anyone point me in the right direction? I'm awful with electromagnetism.

I had 2 questions: 1. My textbook derives that the equation from lenz's and faraday's law emf = - d(N*flux)/dt = B * dA/dT where dA/dt = length * speed However, why does the N value disappear in the new equation? Also, this question is given after: 2. A metal propeller...

A charge Q at a vertex of a square and another Q on the opposite corner of the square and other two charges q each of the other vertices. If the force eletrogmanetica on Q is null which the value of Q in terms of q? There is a q such that the resultant force on 4 charges is zero? My attemp...

My question is not for a specific problem, but in general. I don't quite understand how to calcuate emf for alternators. I will give an example or two to give you an idea. Homework Statement Example 1) A star-connected alternator on infinite bus vars supplies 500MW at 23kV at a power factor...

Homework Statement See picture for clarity. There are 2 infinite wires carrying a current i, one wire does it in the upward direction and the other wire in the downward direction. They are separated by a distance L+2d. Between them lies a circuit such that the part that moves with a velocity v...

I'm trying to wrap my mind around the concept of metals dissolving in water under different electrical potentials. For example, platinum is know to dissolve in liquid water when subjected to 0.65-1.1V. Why does this happen? I'm guessing it has something to due with water being so polar but why...

hi I am new member of this forum..Plz tell me how to use this forum & how to ask Question from other members...Plz tell me differences b/w emf & voltage,Resistance & resistivity..

A conducting rod moves with a constant velocity v in a direction perpendicular to a long, straight wire carrying a current I as shown in the figure below. Find the EMF It should equal U_o*V*L*I/2*pi*r, but how do I get there?

-ve sign in expression of "induced emf" What is the concept behind putting negative sign in: e=-[rate of change of flux] Which direction does it signify?? How does direction affect the equation? How and where can we use negative sign in other expressions of induced emf??

Homework Statement An oscillating emf drives a series combination with circular plates with emf of (170V)sin[400 rad/sec)t], resistance of 0.9 megaohms, radius of 42 cm, and a separation of 1.9mm. Find the rms current in the resistor. Find the rms value of the displacement current between...

Homework Statement A 3 m long large coil with a radius of 15.7 cm and 130 turns surrounds a 7.2 m long solenoid with a radius of 5.7 cm and 4700 turns. The current in the solenoid changes as I=I_0 sin (2\pi f t) where I0= 30 A and f=60 Hz.Inside solenoid has 4700 turns and outside coil has...

Homework Statement A flat loop of wire of area 15.7 cm2 and 1.09 turns is perpendicular to a magnetic field whose magnitude decays in time according to B = 0.5 e−t/7. What is the maximum induced emf? Answer in units of V. Homework Equations \epsilon= \Delta\PhiB/\Deltat \epsilon=...

Homework Statement A little bit of background, my Phys 2 w/Calc class has only covered up to chapter 30(Inductance) in Fundamentals of Physics by Halliday/Resnick. I'm not even sure why this was my homework(turned it in partially completed with written physical reasoning, a picture, and a...

Basically I have been given this question: A battery of unknown EMF and internal resistance is connected in series with an ammeter and a resistance box. The current was 2.0A when R= 4.0 Ohms and 1.5A when R= 6.0 Ohms. Calculate the EMF and internal resistance. I feel you may have to...

This is not a homework problem due. It's practice. I have the answer of .198mV. I don't know how to get it. Homework Statement Homework Equations \phi_b = \int \vec B \cdot d\vec A E = -\frac{d\phi_b}{dt} The Attempt at a Solution The magnetic field due to the solenoid is...

Homework Statement A solenoid of length 3.7 cm and diameter 0.95 cm is wound with 160 turns per cm. The current is decreasing at a rate of 38.0 A/s. (a) What is the induced emf in one of the windings? (b) What is the induced emf in the entire solenoid? Homework Equations emf =...

Homework Statement A circular coil with 35 turns of wire and a diameter of 19 cm is placed in a magnetic field given by B(t) = 6 t^2 + 6 t + 2 T where t is time in seconds. The field is perpendicular to the plane of the coil. What is the induced EMF at t = 5 s? Homework EquationsE=-d(magnetic...

Homework Statement A battery has an emf E and an internal resistance r. IT is connected to an external resistor R. When R=4 ohms, the potential difference is 9.5 V. When R = 6 ohms, the potential difference is 10.0 V Homework Equations The Attempt at a Solution Rtotal = R + r I =...

Homework Statement Need to draw a graph of the emf generated by a simple single-phase generator which has a coil of 200 turns. The coil is 14cm long and 9cm wide. The magnetic field in the generator is 0.15T. The generator coil is turned at a rate of 3000 revolutions per minute. Can someone...

Homework Statement Which one will produce e.m.f? (i) A circular coil placed in a non-homogenous magnetic field (ii) A circular coil moved with constant velocity in a homogenous magnetic field (iii) A circular coil moved with constant velocity in a non-homogenous magnetic field (iv) None of...

Does the emf of a battery remain its specified value for a long time. It is under discharging when connected to the external resistor, so shouldn't its emf value continuously decrease in that case? A battery's emf value increases from 0(completely discharged state) to the specified value...

Homework Statement A magnetic field is perpendicular to the plane of a single turn circular coil. The magnitude of the field is changing so that the emf of 0.80 V and a current of 3.2 A are induced in the coil. The wire is then re-formed into a single turn square coil, which is used in the...

[b]1. Derive an equation to find the induced EMF on an inner solenoid by a changing current on an outer solenoid. Homework Equations We're given the equation EoRMS=(No*Ai*(2*pi*f)*(permeability constant)*IiRMS)/Li for the induced EMF on the outer solenoid by a changing current in the...

Homework Statement A spacecraft is in a circular orbit of radius 3.1 X 10^4 km around a 1.9 X 10^30 kg pulsar. The magnetic field of the pulsar at that radial distance is 1.4 X 10^2 T directed perpendicular to the velocity of the spacecraft . The spacecraft is 0.20 km long with a radius...

Homework Statement A rectangular coil of 200 turns has a length of 200 mm and width 120 mm. The coil rotates with a constant angular speed of 1200 revolutions per minute about an axis through the midpoints of its longer sides in a uniform magnetic field of 2.4 x 10-2 T. Starting from a...

Homework Statement Hi, I found the following example in a high school physics book about electrical circuits. There's something about the example that I don't get, so I hope you can help me out. I give you the example text and the solution, and then I explain what I don't understand...

Homework Statement This is the solution to one of the problems I came across: In an AC generator, a coil spins in a magnetic field. Of the following choices, circle the one that will not cause an increase in the EMF generated in the coil? a. replacing the coil wire with one of lower...

Homework Statement two identical cells of emf E and internal resistance r are connected in series. a 7 ohm resistor is connected across the combination and draws a current of 0.333A. the two cells are now connected in parallel; the 7 ohm resistor now draws a current of 0.375A from the...