Emf Definition and 902 Threads

I am currently studying for a Magnetism and Electricity exam coming up. I was just wondering, within the topic of Electromagnetic induction; my textbook states that if an armature coil of some sort -either from an AC or DC generator was placed horizontally into a magnetic field that is also...

Apologize in advance for the long post! We are in this particular situation and, being a novice with electrical- related issues, would greatly appreciate opinions here. After a year long search, we found this nice home in Texas meeting all requirements my wife and I were looking for, and at...

This thing has confused me for long .I have not come across any satisfactory answers on my own or while browsing through the internet. Everybody has seen the example of a rod moving while on parallel rails, with magnetic field perpendicular to the plane of loop formed by rod and rails...

Then what gives the energy to create this emf?

I understand how motional EMF is produced, the magnetic force separates the charges in the rod to create an EMF. I don't understand though, why the current would flow from a lower potential to a higher potential. I'm sorry I've made like 3 threads in the past 2 days, trying to contribute where...

Homework Statement http://web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide10.pdf pg: 10-17 Homework Equations The Attempt at a Solution I do not understand conceptually, why we chose the rectangular surface to take the flux over. Can anyone explain this...

Homework Statement A relay is required to operate 800m from its power supply, The power supply has negligible internal resistance. The relay requires 16V and a current of 0.60A to operate A cable connects the relay to the power supply and two of the wires in the cable are used to supply...

I was reading this: http://web.mit.edu/8.02t/www/materials/StudyGuide/guide10.pdf (specifically page 10-6), and came across the formula; ## \mathcal{E} = -Blv## which is used for motional emf. Next, I was trying to solve a problem on page 10-33 (bottom problem) with a spinning bar...

Homework Statement the ans is C for this question. i really have no idea , van someone explain please? Homework Equations The Attempt at a Solution

Homework Statement In the circuit shown in the figure, the switch S is closed at time t=0 with no initial charge on the capacitor. What is the induced emf if the inductor at time t=0? Homework Equations ε=-LdI/dt The Attempt at a Solution Initially the inductor acts like a broken...

I have quite a few questions so I've attached the associated images instead of making multiple threads. I'll share my attempts/reasoning for the problems and please tell me if my logic is flawed or if I am doing something completely wrong. Question 41: Bulb brightness is related to power...

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)=(15.0A)sin(2500t) where t is in seconds. The distance a is 12.0 cm, and b is 15.0 cm. Homework Equations emf = Δmagneticflux/Δt...

Homework Statement (Challenge Problem 80, Ch33) A rectangular metal loop with 0.050 ohms resistance is placed next to one wire of the RC circuit shown in the below figure. The capacitor is charged to 20 V with the polarity shown, then the switch is closed at t = 0s...

Homework Statement A rectangular wire loop, 24mm by 36mm, is placed in a magnetic field. The flux density perpendicular to the loop is decreasing in magnitude at a rate of 0.2Wb/m^{2}/s. Calculate the induced emf around the loop. Homework Equations The problem is I don't know which...

The question is: a conducting spherical shell of radius a rotates about the z axis with angular velocity ω, in a uniform magnetic field B= B_{0}\hat{z} . Find an expression for the EMF developed between: i) the north pole and the equator (2 marks); ii) the north pole and the south pole (1...

A metal bar with length L, mass m, and resistance R is placed on frictionless metal rails that are inclined at an angle α above the horizontal. The top end of the rails are connected with a conducting wire. The resistance of the rails and wire are negligible. The rails are embedded in a uniform...

Homework Statement A rectangular coil of wire has 65.0 turns and is 30.0cm by 43.0cm . Initially the plane of the coil is perpendicular to a uniform external magnetic field. It is then rotated till its plane is at an angle of 35.0∘ with that field. The magntude of the external field is 1.90T...

Hello everyone, I'm a bit confused about the power drawn by a motor. Since back emf reduces current when the motor is rotating at high speed, is it true that back emf reduces the power required at high speed? THX :D

Hi everybody, I was wondering how much induced EMF would be produced in a 20cm diameter coil with 100 loops produce. Has anyone conducted such an experiment? I am interested in quantitative values of the experiment. Thanks, KB

According to my book, if we connect a high resistance in series to the secondary cell (whose emf is to be balanced) , connect this whole apparatus to a potentiometer with an auxiliary Emf and find the null point . It's written that even after removing the Hugh resistance the null point comes...

I need help in understanding back emf, I'm a bit confused here. Example(for understanding): Let's assume we have a 12 V DC motor, that draws 20Amps when it starts, as it reaches maximum speeds, current drops due to back emf, let's assume the resistance is 0.6 ohms, and b.emf = 10V...

I have proven the induced emf between the centre and rim in a circular disc of radius a and angular velocity w, with a magnetic field B parallel to its axis is 0.5wa2B. I need to find the time taken for the disc to slow to half it's initial speed ignoring friction, given a resistance R is...

Homework Statement A conducting bar of length L moves with velocity v, in a rectangular region with a uniform and stationary magnetic field B_1. Near the bar, there is a cylindrical region of radius R with another magnetic field B_2 (it may vary on time). Both magentic field are normal to the...

Hi guys, I'm pretty sure this has been answered somewhere around here. So, consider a pure inductance (zero resistance) connected in series to a battery. We know that the magnitude of the induced voltage across the inductor is given by E=L\normalsize\frac{di}{dt}. According to KVL...

Homework Statement I need to know what effect wire heating would have on the reading of the EMF of a battery, and how the heating effect can be reduced! Homework Equations V= IR The Attempt at a Solution Well I know that the heating effect increases the resistance in the wire...

The attached drawing represents 4 wires. The top and down are still. The right and left move with the same velocity v as shown by the arrows. There is a magnetic field perpendicular to the page. Will there be a current flowing through the circuit formed by the 4 wires?

Homework Statement A uniform magnetic field B is perpendicular to the plane of a circular wire loop of radius R. The magnitude of the field varies with time according to B=B0exp(-t/τ) where B0 and τ are constants. The time dependence of the induced emf in the loop is a) exp(-t2/τ2) b)...

In the case of self induction, when the intensity increases gradually an emf is induced which generates a back current " equal in magnitude, opposite in direction " to oppose the increase, so if that is right shouldn't the intensity in the coil Become ZERO till the intensity becomes steady?

when turning on a d.c circuit connected to a very simple solenoid, does the backward emf ever reach the source emf ? if it does then how does the current continue to flow ?

Homework Statement a coil starts perpendicular to a magnetic field of 0.365 tesla , it has a length of 0.15 cm and a height of 0.25 cm , it rotates with a frequency of 1800 rotation / min . it also has 30 turns calculate the mean induced Emf during quarter a rotation Homework Equations...

Hello , I have a question , assuming ideal devices here without losses for the sake of simplicity. Imagine I have a circuit like the one attached. Now if I would manage to flip either one of the switches fast enough that the switch is cut off right when the magnetic saturation of the...

Correct me if I am wrong. For a RL circuit, I know as a fact at t=0, there is a back emf that is almost equivalent to the original emf source. In order for the back emf to exist, there needs to be a magnetic field in the inductor. In order for there to be a magnetic field in the inductor...

> A very long straight wire carries a current I. A plane rectangular coil of high resistance, with sides of length $a$ and $b$, is coplanar with the wire. One of the sides of length $a$ is parallel to the wire and a distance $D$ from it; the opposite side is further from the wire. The coil is...

Consider a magnetic field perpendicular to a conducting ring moving with a velocity, v.When the ring is moving on the ground in translational motion alone, will emf be induced? I am slightly confused because if you consider the two halves of the ring as two rods, emf will be induced in both of...

Homework Statement Homework Equations The Attempt at a Solution Well I tried this (I thought it'd work, but it's not the right answer and I'm not sure how to do it now) Anyway this is my attempt: \Phi = \mu_{o}\frac{NIA}{\ell} \\ \varepsilon=N\frac{d\Phi}{dt} So then...

Homework Statement A step down transformer, 2400/240 V, 50Hz has the following resistance and leakage parameters. Z1 = R1 + jX1 = 4 + j12 Ω Z2 = R2 + jX2 = 0.04 + j0.12 Ω The transformer is operating at 80% of its rated load. The power factor of the load is 0.866 leading. Determine the...

Homework Statement A wire loop of resistance R and area A has its normal along the direction of a uniform magnetic field, B. The loop is then flipped over in a time Δt so that its normal is opposite to the field. a) Calculate the average induced EMF. b) Find the average induced current. c) If...

Hello, Please i have a question.When we have an inductor in a circuit we say that we have 2 electric field : conservative and non-conservative. so who is doing work on the charges?if we draw an rl circuit with a DC source the conservative electric field across the inductor has the same...

Consider an ideal solenoid (no resistance, no leakage reactance etc.) connected across an AC supply. The back EMF induced in it will be exactly equal and in opposite direction to the source voltage (which means that when a certain terminal of the AC supply is positive, the side of solenoid...

Hi there i need a tutorial of how EMF works in an electric guitar and also which formulae is more suitable for solving EMF in the electric guitar thank u

Homework Statement An infinite straight wire carries a current I that varies with time as shown above. It increases from 0 at t = 0 to a maximum value I1 = 3.7 A at t = t1 = 14 s, remains constant at this value until t = t2 when it decreases linearly to a value I4 = -3.7 A at t = t4 = 30 s...

A single-turn circular loop of radius R = 0.197 m is coaxial with a long 1740 turn solenoid of radius 0.0410 m and length 0.890 m, as seen in the figure below. (picture in URL)...

1. Assuming that both the windings of a transformer is wrapped around an iron core, how is an EMF induced in the secondary winding - isn't it necessary for flux to cut through the winding in order to induce an EMF? The flux cutting through the winding would apparently be very low..as most of it...

Homework Statement Consider the following sequence of reactions occurring in the acid medium. All emf (standard) are measured at ##25^{\circ} C## and expressed in volt unit: $$MnO_4^-\stackrel{0.564}{\rightarrow}MnO_4^{2-}\stackrel{2.26}{\rightarrow}MnO_2\stackrel{0.95}{\rightarrow}Mn^{3+}...

Homework Statement I don't understand why the answer in this problem is choice A. http://grephysics.net/ans/9277/57 I'm confused. Lets say the semi circle is FULLY outside of the circle. For awhile after that, the semi circle would be accelerating the rate at which a certain % of it is...

1. a. coil is moved up and down in the same direction of flux. b. coil is rotated around an axis that is parallel to the flux. c. coil is rotated to the direction of the flux like a dynamo. 2. Electromagnetic inductions laws. 3. I'm really having a hard time...

In the classic problem of the induced EMF in a moving conductor (as in the picture above), the calculation for the induced EMF is as follows E=\frac{d\Phi_B}{dt}=\frac{d(BA)}{dt}=\frac{Bd(A)}{dt}=\frac{Bd(Lx)}{dt}=\frac{BLdx}{dt}=BLv. The derivation assumes that the magnetic field B is...

Hi, I work in the construction industry. I have a homeowner that would like to protect herself from electromagentic field (EMF) exposure. (She fears cancer from EMF's.) The airconditioning unit in their AC room produces a large electromagnetic field. She wants to prevent this field from...

Hi, My interest in physics is relatively new and recently I've been trying to figure out the answer to what is probably a simple question. Here it is; if one is using an AC EMF meter to read the time varying current from a man-made electromagnetic field, will brandishing ferromagnetic...

Ok, so I'm doing an experimental write up for an experiment on adjusting voltage on the speed of a simple DC motor, and changing the number of coils. I thought that I understood what I was saying but I've recently become a little confused with the concepts of torque vs speed specifically when...