Emf Definition and 902 Threads

Homework Statement What is the average emf created by a 15 turn cable that is .5 meters in diameter, lies flat with the surface of the Earth and is flipped 180 degrees in 2 seconds? *Assume the Earth produces a magnetic field of .5 micro Tesla. Homework Equations e=-n*r^2*delta...

Homework Statement Determine the emf induced in the square loop in the figure if the loop stays at rest and the current in the straight wire is given by I(t) = (15.0 A)sin(2500t) where t is in seconds. The distance a is 12.0 cm, and b is 15.0 cm. Homework Equations In the question...

Homework Statement A simple generator has a coil with dimensions 1.0 cm x 1.0 cm which is rotated at 60 Hz in 1.0 T magnetic field. How many windings (turns of wire) are needed to generate a peak emf of 120 Volts ? Homework Equations 1. emf E = - d (magnetic flux) / dt 2. magnetic flux = (B...

I'm relatively new here, but I felt that you guys might be able to help me. I'm trying to design a directed electromagnetic field generator with a variable field strength and oscillation rate. What I'd really like to know is exactly how difficult would this be? My EE experience is rather...

Homework Statement [PLAIN]http://img220.imageshack.us/img220/2589/44045733.png Semicircular wire MN of diameter L moves with speed v perpendicularly through a uniform magnetic field of strength B. 1. Find the magnitude of the induced emf generated between M and N. 2. State whether M...

Sometimes when i swipe my card at walmart it doesn't read it , And the guy was like let's put it a plastic bag and then try it, and it works and I've heard a couple of other people doing this. So when i slide my card the magnetic strip induces a voltage and reads the card. So why does...

In power plants alternating emf is generated by rotating loop in magnetic field which is directly proportional to angular velocity of turbine.I think it is highly impossible to maintain angular velocity of turbine constant(especially in hydro power plants).Then how are they supplying a...

Part A Find the emf E1 in the circuit of the figure . = Part B Find the emf E2 in the circuit of the figure. = Part C Find the potential difference of point A relative to point B. A) I wrote a KVL using the top loop. First I found out what the current...

Hi! I'm trying to fully grasp why the potential drops when an internal resistance is present in a source of emf. At first I thought that yes it would be harder to "push" the charges to the higher potential, but once there, why shouldn't the higher potential be the same as before? Just as if a...

Homework Statement coils rotating in a magnetic field are often used to measure unknown magnetic fields. As an example, consider a coil of diameter 2.00 cm with 72.0 turns that is rotated about an axis perpendicular to the field at a rate of 20.0 Hz. If the maximum induced emf in the coil is...

Will u tell me what is back emf?

I have always wondered if anyone has ever developed an understanding of why Back EMF happens? All I know is it happens when the the field inside of a transformer collapses at some low frequency during the collapse of the coil when the transistor shuts off creates a huge spike hundreds of...

First of all this isn't really Homework problem, but since it is based on homework problem, I'll post on this section of the forum. Feel free to move if I was supposed to post on different part of the forum. Either way, I'll use homework as an example since that is what brought this up...

Homework Statement A generator has a 170-turn square coil, 5 cm on a side. Find the peak emf in this coil when it's rotating at 90.0 Hz in Earth's field, 5*10^-5 T Express your answer to one significant figure and include the appropriate units. Homework Equations Emf = NBAw The...

Let us consider a rectangular plate moving horizontally in a vertical magnetic field with its length perpendicular to its direction of motion.This may be closely approximated by the wing of a flying aircraft.The axial emf is given by the traditional formula, E=BLV. Now when the...

Homework Statement The positive terminals of two batteries with emf’s of E1 and E2, respectively, are connected together. Here E2 > E1. The circuit is completed by connecting the negative terminals. If each battery has an internal resistance r, the rate with which electrical energy is...

Any help appreciated with these! Homework Statement 1. A battery is made up from a series combination of six 1.2 volt nickel cadmium cells supplying a 10ohm load- a) What is the open circuit voltage? b) Ignoring internal resistance, what is the current flowing in each cell? 2. The nickel...

Electromotive force is usually defined as the work done in transporting a unit positive charge in a round trip in the circuit. That is, EMF= loop integral of E.dL Now let us examine the above statements in the light of a constant source of emf driving a steady current in the circuit. If the...

Homework Statement The question itself doesn't make sense to me, it says to find emf but the answer box has V= ? problem is an attachment. Homework Equations I=e/(r+R) Ir+IR=emf P=VI The Attempt at a Solution If it wants voltage that's simple P=I^2R P=V^2/R V=54.8V if...

Homework Statement An infinite cylinder (radius a) with a uniform volume charge density rho_v is given. The axis of the cylinder coincides with the z axis. The following magnetic field exists: B=B0cos(wt+a) for r<=a (i.e., inside the cylinder and on its walls) B=0 for r>a...

Homework Statement A battery supplies a steady current of 5.6 A for 21 s. During this time 1410 J of chemical energy is transformed into electric energy, but 560 J of this electric energy is transformed into heat energy inside the battery. What is the total power output of the battery...

Homework Statement C alculate the emf (in volts) induced in a loop of wire if the magnetic flux in the loop increases from zero to 71.1 milliweber in 16.7 millisec. Homework Equations faradays Law The Attempt at a Solution The only law I know is faradays law which uses Area...

Homework Statement There is a Static magnetic field,with its intensity B. Assume a coil moving in the magnetic field, with its position function y=asinwt. then calculate the voltage of U Homework Equations The Attempt at a Solution

Homework Statement A square of side 2cm, in the first quadrant of the x-y plane, with a corner at the origin, is in a magnetic field pointing out of the page of magnitude 4t2y. Calculate the emf around the square at t = 2.5s and give its direction.Homework Equations \epsilon = - \frac{d}{dt}...

Homework Statement A flat coil of wire consisting of 20 turns, each with an area of 50 cm^2 is positioned so that the normal to its plane is at the angle of 30 degrees to a uniform magnetic field that increases its magnitude at a constant rate from 2.0T to 8.0T in 2.0 s. Homework Equations...

Consider a rotating disk on a uniform magnetic field. Faraday's law states that \epsilon = - \frac{d\phi}{dt} In this situation, \vec B is constant and the area of the disk is constant. Hence, the magnetic flux is constant and there should be no emf. What am I missing?

Homework Statement A 25-turn circular loop of wire has a diameter of 1m. In 0.2 seconds it is flipped 180 degrees at a location where the magnitude of the Earth's magnetic field is 50 micro T. What is the emf generated in the loop?Homework Equations -(dB/dt)(A)=VThe Attempt at a Solution When I...

Question: A voltaic cell is constructed with two silver-silver chloride electrodes, each of which is based on the following half-reaction: AgCl(s) + e- = Ag(s) + Cl-(aq). The two cell compartments have [Cl-]= 1.41×10−2 M and [Cl-]= 2.70 M, respectively. What is the emf of the cell for the...

1. How fast would you have to drive your car to create a 3.0 V motional emf along your 1.2 m-long radio antenna? Assume that the motion of the antenna is perpendicular to B. 2. d(phi)/dt = EMF dphi = B*A v = dx/dt 3. I'm really not sure here. I think the length of the antenna...

1. A 100-turn, 2.0-cm-diameter coil is at rest in a horizontal plane. A uniform magnetic field 60 degrees away from vertical increases from 0.50 T to 1.50 T in 0.60 s. 2. EMF = N*d(phi)/dt phi = flux = ABcos(theta) 3. dB/dt = 1/0.6 EMF = 1000*(1/0.6)*pi*r2*0.5 = 0.262 V Is...

Homework Statement A solenoid with a length of 25.0 cm, radius 1.60 cm and 5500 turns carries a current of 1.50 A. A small coil of radius 1.05 cm and 130 turns is placed at the center of the solenoid with its axis in the same direction as that of the solenoid. A 470 ohms resistor is connected...

Here is how the question is stated exactly: A circular conducting loop is held fixed in a uniform magnetic field thatt varies in time according to B(t) = B0exp(-at) where t is in s, a is in s-1 and B is the field strength in T at t=0. At t=0, the emf induced in the loop is 0.0758 V. At t=...

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 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...