Emf Definition and 901 Threads

the emf is defined as the potential difference between two points \varphi(\vec{r_1})-\varphi(\vec{r_2}). ok so let's say we make a trip round a closed circular wire with a battery to keep the current flowing then r1=r2 and so no emf has been done - is this true and if so why?

Faraday's law says induced emf = - d(flux)/dt If this is applied to a loop where induced emf causes currents, and thus flux itself, do we have to consider that flux (of course we don't if it's constant)? If the external flux has a nonzero second derivative, then the induced emf is...

Homework Statement A real battery is not just an emf. We can model a real 1.5 battery as a 1.5 emf in series with a resistor known as the "internal resistance", as shown in the figure (Intro 1 figure) . A typical battery has 1.0 Ohm internal resistance due to imperfections that limit...

Homework Statement 1. When a 100 loop coil of wire of radius 2.00 cm is rotated in a uniform magnetic field,B=0.500T , so that it goes from maximum flux to zero flux in 0.0320 s, find the average emf induced between the terminals of the coil.Homework Equations Max Flux=BAcos(0)=Change in...

Two straight conducting rails form a right angle where their ends are joined. A conducting bar in contact with the rails starts at the vertex at time t = 0 and moves with a constant velocity of 7.00 m/s along them, as shown in Fig 31-44. A magnetic field with B = 0.350 T is directed out of the...

Homework Statement Homework Equations e=d/dt(BAN) The Attempt at a Solution

Hi, I have a problem about EMF and/or Voltage. Let their are 100 electron at a place A and 200 electron at place B. Now what will be the Voltage/EMF (Voltage or EMF difference)? And How to calculate it ?? In other words "How can I calculate Voltage or EMF if I know only Charge...

Homework Statement The component of the external magnetic field along the central axis of a 50 turn coil of radius 4.7 cm decreases from 1.8 T to 0 T in 4.3 s. If the resistance of the coil is 2.8 , what is the magnitude of the induced current in the coil? Homework Equations...

Homework Statement A 11.2m long steel been is dropped from a height of 9.51m. The horizontal component of the Earth's over the region is 18.5x10^-6T. What's the emf in the beam impact just before the impact with the earth, assuming its long dimension remains in a horizontal plane, oriented...

If a cell is connected with an external resistor of 6V and a switch and a voltmeter is connected across the terminals of the cell which reads 2.6 V when the switch is open and 2.4 V when the switch is closed, how do you find the emf and the internal resistance? so far i tried doing: V = IR...

A motor with a brush-and-commutator arrangement has a circular coil with radius 2.5 cm and 150 turns of wire. The magnetic field has magnitude 0.06 T and the coil rotates at 440 rev/min.What is the average back emf? i have tried this Flux=Magnetix Field*Area Flux=0.06*pi*r^2 Here...

Homework Statement A 800-turn solenoid, 18 cm long, has a diameter of 2.9 cm. A 15-turn coil is wound tightly around the center of the solenoid. If the current in the solenoid increases uniformly from 0 to 3.1 A in 0.28 s, what will be the induced emf in the short coil during this time...

Hi, I'm trying to figure out how you can calculate motional EMF when the velocity of the object in question is not perpendicular to the magnetic field. There are two equations in my textbook, but the text describing them is not very helpful. The first is \varepsilon = vBL, which can be...

Homework Statement Resistance = R Radius = r Angle = theta B = 2cos(2t) Circular wire loop where magnetic field acts at theta degrees with respect to the normal of the wire loop. Find induced current and emf in wire loop. Find induced electric field at radial distance d from center of wire...

I need some help in appreciating this consensus. We are told the following things: - that we have anti-electrons, anti-protons but no anti-photons. - that photons - or more specifically emr - have an electrical component and a magnetic component. - the the magnetic component of emr runs 90...

How are a battery's emf and its terminal voltage different? Can they ever be the same value?

So here is the circuit I came up with to represent back emf in a DC motor with rotational inertia. When current is applied to the motor it spins. When it rotates, the motor acts as a generator and creates a voltage (back emf) as shown (sorry for the incorrect notation, I don't know the...

(As magnitudes) Faraday's law states that induced emf in a conducting loop by a changing flux, say x, is: emf = dx/dt Now if we have a circuit with the loop in series with wires (which are then tied together), how do I picture the voltages/currents in this circuit? I mean, the actual...

See question below: http://img140.imageshack.us/img140/479/30680788kr3.th.jpg In order to calculate the EMF, the markscheme using the formula "E=Blv", the markscheme uses the linear speed of point M. Can someone please explain why this is the case - I understand the derivation of E=Blv, just...

I realize this is probably a very simple question, but for some reason I'm getting very confused. Homework Statement A motor is connected to a 12 V dc supply and draws 5.0 A when it first starts. What will be the back emf when the motor is operating at full speed and drawing 1.2 A...

A coil is located at the center of a long solenoid of radius R = 15cm which has 5x10^7 turns per meter and carries a current I = 16A. The coil is coaxial with the solenoid and consists of 5 turns of wire each in the shape of a square of length a = 5cm on each side.What is the magnetic flux...

The question was to find I1 I2 and E. I got those parts of the question correct. I1= 1 A I2 = 2A E = 15V. But the only reason I got these right is because the arrows for I1 & I2 were given in the attached figure. The directions of the current don't make sense to me. If the EMF from...

Homework Statement In the figure below, R1 = 5.50 , R2 = 18.0 and the ideal battery has an emf E= 12.0 V. (a) What is the size and direction of current i1? (Take right to be positive.) (b) How much energy is dissipated by all four resistors in 1.00 min? Homework Equations I = E/R...

Homework Statement Review problem. A flexible metallic wire with linear density 3.00 multiplied by 10-3 kg/m is stretched between two fixed clamps 64.0 cm apart and held under tension 301 N. A magnet is placed near the wire as shown in Figure P31.25. Assume that the magnet produces a uniform...

Homework Statement A 32 turn circular coil of radius 4.60 cm and resistance 1.00 is placed in a magnetic field directed perpendicular to the plane of the coil. The magnitude of the magnetic field varies in time according to the expression B = 0.0100t + 0.0400t2, where t is in seconds and B is...

A long, straight wire is in the same plane as a wooden, non-conducting loop. The wire carries an increasing current I in the direction shown in the figure (the current is pointing in the left direction). a. there will be no induced emf and no induced current b. there will be a...

Homework Statement A 26.4 cm diameter coil consists of 23 turns of circular copper wire 1.90 mm in diameter. A uniform magnetic field, perpendicular to the plane of the coil, changes at a rate of 8.00E-3 T/s. Determine the current in the loop. Part Two: Determine the rate at which thermal...

motional emf i think... change in area and magnetic field Homework Statement A rectangular loop is located in a uniform magnetic field of magnitude 0.29 T directed perpendicular to the plane of the coil. If the area of the coil increases at the rate of 5.2 10-3 m2/s, what is the magnitude...

Homework Statement A single coil with a radius of .02m is placed inside a 3m long solenoid that has 600 turns. The radius of the solenoid is 0.15m. The plane of the coil is perpendicular to the axis of the solenoid. The solenoid is connected to a battery, an ammeter and a switch. The ammeter...

Homework Statement Find I1.Find I2. FInd emf. emf is that E like symbol in the picture http://session.masteringphysics.com/problemAsset/1075283/3/32.P50.jpg Homework Equations I=V/R I=emf/R The Attempt at a Solution this problem is frustrating. i tried using kirchhoff's loop law

Homework Statement Suppose you have a coil that is a certain distance from a magnet. Now you move the coil towards the magnet (until it is on top of the magnet) at a certain speed. Then you do the same thing only faster. Will the total induced emf be the same for both tries? Aka should the...

Homework Statement A square, single-turn wire loop 1.00 cm on a side is placed inside a solenoid that has a circular cross section of radius 3.00 cm, as shown in the figure below. The solenoid is 16.0 cm long and wound with 95 turns of wire. (a) If the current in the solenoid is 3.00 A...

When switch S in the figure is open, the voltmeter V of the battery reads 3.07 V. When the switch is closed, the voltmeter reading drops to 2.95 V, and the ammeter A reads 1.70 A. Assume that the two meters are ideal, so they do not affect the circuit. Find the value of the emf. (see picture...

induced emf in secondary coil - help ASAP Please Homework Statement A very long, straight solenoid with a cross-sectional area of 6.00 cm2 is wound with 40.0 turns of wire per centimeter, and the windings carry a current of 0.250 A. A secondary winding of 2.00 turns encircles the solenoid...

Hello all, first time post here. I was curious, hypothetically, how much juice would you need to generate a 400,000 Gauss magnetic field?

Homework Statement A torch bulb is marked 2.5V and 0.3A. When it is connected to a dry battery of e.m.f 3.0V the correct p.d of 2.5V is produced across it. Calculate the internal resistance if the battery.Homework Equations I=V/R?The Attempt at a Solution It's on paper - sorry!Answer = 1.67 -...

\xi = - \frac{dB}{dt} Is the emf induced by a changing flux. Is the current created by this emf conventional current? For example. Say there is a square loop in the plane of this page, with a decreasing magnetic field going INTO this page. This creates a clockwise current to battle the change...

Finding the EMF of the cell... first post =) Homework Statement Find the EMF of the cell. (diagram has been uploaded) Homework Equations Resistors is series : Rs= R1 + R2 + R3 Resistors in parallel: 1/Rp = 1/R1 + 1/R2 + 1/r3 V=IR The Attempt at a Solution Firstly i re-drew...

[SIZE="1"]Couple of months ago Deany100 posted a note on microwave radiation which he suspected was his neighbour tracking his movements. I've got a similar problem, a home bathed in emf picked up by a device (15 pounds sterling) that doesn't tell me what the frequency is. Great disbelief from...

How back emf helps in energy conversion in a motor? hello, I am an engineering student and during the past few days i was searching on the net to clarify my doubts on "motors".So i came across an article and on reading one part of it a doubt arosed in my mind. Q1) "To take a practical...

Homework Statement Can there be an electric current without an e.m.f.? (i noticed my mistake in the title, it should be e.m.f. not EMF)I was given this question and I don't know how to answer it, any help would be greatly appreciated

An elastic conducting material is stretched into a horizontal circular loop of radius 20 cm and placed in a magnetic field of strength 0.5 T, directed vertically downwards. a. What is the magnetic flux through the loop? b. When released, the radius of the loop decreases at an initial rate...

If i have a series DC motor and at say X rpm it has a back emf of 11.5v and supply voltage of 12v and i increased the supply voltage (keeping rpm the same) would the back emf stay the same? and if not would the diffrence between back emf and supply increase? Thank you.

Homework Statement There is a circuit which consists of a capacitor with capacity C, a diode and a source of changing EMF such that during time \frac{1}{2}T EMF equals E and during another half of T it is -E (current flows in the opposite direction). What will be the voltage on the capacitor...

Homework Statement A generator is constructed by rotating a coil of N turns in a magnetic field B at a frequency f. The internal resistance of the coil is R and the cross sectional area of the coil is A. Which of the following statements are true? (Give ALL correct answers, i.e., B, AC...

[SIZE="3"]Homework Statement CELLS OF EMFS E1 ,E2,E3...HAVING INTERNAL RESISTANCES r1,r2,r3...are connected to an external resistance R.What is the resultant emf? Homework Equations The Attempt at a Solution[FONT="Arial"]

The Carrier of an Emf is in many definite/indefinite parts the net of the circuits Total Resistance (Rt). These definite/Indefinite parts are the SMALLEST degree expressed to that of a single atom, the basic Resistive properties or qualities of Itself, and the electron structure as pertaining to...

Homework Statement A circular coil, with radius of 10 cm, and 25 turns, rotates in a constant magnetic field of strength 2.4 T, with the axis of rotation perpendicular to the direction of the magnetic field. (a question about finding the induced voltage- 5.92 V) part C. If the...

Ex:At home, you plug an electric drill into an electrical outlet and turn it on. At the moment you turn on the drill, the lights in the room(wired in parallel to the drill) flicker and dim briefly, but then return to normal after a moment. notice that the example is wired in parallel, but in...

A slide wire (resistance R) travels without friction along the track shown below. It starts from position x0 (non-zero) and velocity v0 , to the right as shown. Assume that the v shaped rails meet at an angle of q. Use the coordinate system shown. The magnitude of the external magnetic...