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# EMF

Electromotive force, also referred to as EMF, is the voltage generated by a battery or by a magnetic force, which states that a time varying magnetic field induces an electric current. The EMF is not a force measured in newton’s, but a potential, or energy per unit of charge measured in volts. In nature, EMF is generated whenever magnetic field fluctuations occur through a surface.

In electromagnetic induction, EMF can be defined around a closed loop as the electromagnetic work that would be transferred to a unit of charge if it travels once around that loop. In time-varying magnetic flux affecting a loop, the electric potential scalar field is not defined due to circulating electric vector field. Nevertheless an EMF works so that it can be measured as a virtual electric potential around the loop.

In a two-terminal device, the EMF can be measured as voltage across the two open-circuited terminals. The created electrical potential difference drives current flow is a circuit is attached to the source of EMF.  When current flows, the voltage across the terminals of the source of EMF is no longer the open-circuit value. This is due to the voltage drops inside the device due to its internal resistance.

In a battery, charge separation that gives rise to a voltage difference is accomplished by chemical reactions at the electrodes.  Chemically, by separating positives and negative charges, an electric field can be produced, leading to an electric potential difference. A voltaic cell is thought of as having a “charge pump” of atomic dimensions of each electrode.

### A Series RLC Circuit

A series RLC circuit (see attached diagram), consists of a 50? Resistor, a 3.30 mH inductor, and a 480nF capacitor. It is connected to a 3.0 kHz oscillator with a peak voltage of 4.10 V. What is the instantaneous emf , ? when i = I ? ____________V What is the instantaneous emf , ? when i = 0A

### Induced EMF and Current in a Shrinking Loop

A circular loop of flexible iron wire has an initial circumference of 163cm, but its circumference is shrinking at a constant rate of 11.0 cm/s due to tangential pull on the wire. The loop is in a constant uniform magnetic field of magnitude 1.00T, which is oriented perpendicular to the plane of the loop. Assume that you are fac

### Discussing Initial Public Offerings (IPO's)

Initial Public Offering (IPO) is defined as the first sale of stock by a company. Companies like AVG (http://www.avg.com/ca-en/homepage) looking to further their growth often use an IPO as a way to generate the capital needed to expand. AVG is uniquely positioned to spearhead innovation in the industry thanks to its employing of

### shunt wound motor draws a current of 45 A when running at full

6. (i) A 20 kW, 500 V d.c. shunt wound motor draws a current of 45 A when running at full load with a speed of 600 rev min-1. On no load, the current drawn from the supply is 5 A. If the armature resistance is 0.3 ohms and the shunt field resistance is 220 ohms, calculate the armature current, speed and efficiency of the motor w

### An RLC Circuit

Question: A series RLC circuit has components with the following values: R = 50.0 Ohms, L= 200.0mH, and C = 10,0 uF. The circuit contains an emf source e(t) = (200V) sin [500 (rad/s) t]. (a) Compute the impedance and phase angle for this circuit. (b) Find an expression for the current i(t) in the circuit. (c) Evaluate th

### Electronic Principles Notation

I have some revision questions from an old test paper. However, I am unable to check if my answers are correct. Please see the attached file for the questions I need answers to. Can you help? Derive the Thevenin's equivalent e.m.f. and impedance as seen between the terminals AB. (Note:You must show the simplified version of

### Magnetic field and Voltage induced

Refer to attachment 1. The rectangular loop in the figure above moves towards the long straight wire with a velocity v. If a current I flows through the wire, what is the voltage induced in the loop when the coil is a distance b from the wire in terms of L, I, v, a and b? How to evaluates the values I = 5A, a = 2cm, b = 2cm,

### Constructing a graph of a self-induced emf across an inductor

** Please see the attachment for the figure ** The current in a 4.20 mH-inductor varies in time as shown in the figure below. Construct a graph of the self-induced emf across the inductor over the time interval t = 0 to t = 12.0 ms.

### Electric Circuit: Loop and junction rules

See attached file for fig. 3. If the ammeter is reading 3.0 A. Assume a direction for the current in the 2.0 ohm resistor. Call it I3. Clearly indicate it on the figure. Clearly indicate which end of each resistor is the highest potential by drawing a plus sign and indicate the lowest potential by minus sign. Write

### Finding the Electromagnetic Frequency of a Battery

In the circuit shown in the attached figure the batteries have negligible internal resistance and the meters are both idealized. With the switch S open, the voltmeter reads 17.0 V. Find the emf (epsilon) of the battery.

### Rank circuits in order of current and net power output of battery

Problem 1 A simple circuit consists of a resistor connected to a battery. The battery has emf (e), internal resistance (r), and terminal voltage (V_ab), and the resistor has resistance (R) . Rank the following circuits in order of current, from highest to lowest values. 1. e = unknown 2. e = 1.4 V r = 0.1 ohms

### Faraday's Law of Induction: induced current

Suppose the current in the infinite long straight circuit C of Figure 13-5 is given by, see attached, Find the induced emf that will be produced in the rectangular circuit of this same figure. What is that direction of the induced current.

### Thevenin's equivalent circuit, Transfer function

Please refer to the attachment for questions complete with circuit diagrams, and provide full answers. 1a) Derive an expression for the transfer function Vout/Vin of the circuit below (assume that no current flows to the output terminals AB). 1b) State whether the circuit can be made to produce an output signal with zero p

### Finding the Induced EMF

A triple turn planar loop of wire has a cross-sectional area of 150 cm^2. The plane of the loop is perpendicular to a magnetic field that increases uniformly in magnitude from 4T to 10T in 30 sec. What is the resulting induced emf and current if the loop has a total resistance of 50 Ohm?

### Magnetic Flux

Figure 5(a) shows a loop of wire placed between the poles of a magnet. The magnetic field can be assumed uniform between the poles. The area (shown shaded) formed by the loop within the field of the magnet is 20 cm^2. (i) Determine the magnitude of the flux density required to induce a maximum voltage of 1 V when the loop is

### Faraday's Law: direction of induced current in the loop; direction of a magnetic force

An N-turn square coil with side l and resistance R is pulled to the right at constant speed v in the positive x-direction in the presence of a uniform magnetic field B acting perpendicular to the coil. At time t=0, the right side of the coil is at the edge of the field. After a time t has elapsed, the coil is in the region where

### Electromotive Force

Please see the attached - Do I use the motional electromotive force equation of vBL or am I way off?

### Gravitational potential at the surface of Mercury

Please refer to the attachment for complete and all the questions. I am looking for brief explanations along with the answer. 11. The gravitational potential at the surface of Earth is V. The radius of Mercury is about one third the radius of Earth. Earth and Mercury are spheres of the same density. What is the gravitational

### Physics Problems: Electricity, Voltage, Conductor, Resistance, Current, Power

1- ) a string of Christmas-tree lights is frequently made of miniature lamps connected in series. For an 8-lamp, 120- volt set what is the voltage across each lamp? If one lamp were removed, what would happen? The voltage across the empty socket becomes equal to the line voltage. Why is this? 2- ) a piece of copper wire is c

### Physics: mutual inductance

A.) Show that the mutual inductance between two coaxial coils separated by a distance z as in figure attatched, one of radius a and N_a turns, and the other of radius b << a and N_b turns is: pi*mu_0*N_a*N_b*a^2*b^2/[2(a^2 + z^2)^(3/2)] Calculate the magnetic flux through coil b due to the current through coil a. B.) H

### Simple circuit: Calculate the resistance of the second resistor

Two resistors are connected in series to a battery with an emf of 7 V. The first resistor is 96 &#937; and the current through the second resistor is 33 mA. Calculate the resistance of the second resistor. Please solve and explain problem.

### Transmission Lines: Example Question

Part 1 If 30.7 MW of power at 45.8 kV (rms) arrives at a town from a generator via 4.46 Ω transmission lines, calculate the emf at the generator end of the lines. Part 2 Calculate the fraction of the power generated that is lost in the lines.

### Generator True and False Questions

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. (True/False) (1)The average induced EMF doubles if the area A is doubled. (2)The average induced EMF doubles if the resistance R is double

### Electro Magnetic Induction: Motional EMF Induced in Antenna

The Voyager I spacecraft moves through interstellar space with a speed of 8.07E+3 m/s. The magnetic field in this region of space has a magnitude of 1.89E-10 T. Assuming that the 5.06 m long antenna on the spacecraft is at right angles to the magnetic field, calculate the induced emf between its ends.

### Grasping for a Loop

Grasping for Loops The flexible loop in the figure below has a radius of 14.1 cm and is in a magnetic field of strength 0.102 T. The loop is grasped at points A and B and stretched until it closes. If it takes 0.245 s to close the loop, find the magnitude of the average induced emf in it during this time.

### Physics: Lenz's Law for direction of induced current in a loop of wire

A loop of wire is lying flat on a tabletop. A uniform magnetic field is directed vertically UPWARDS such that it is perpendicular to the tabletop (and the loop). Beyond the edge of the table, the magnetic field is zero. Imagine that you are looking DOWN on the loop from above. Which of the following statements are true about the

### Physics: Loop of wire in a uniform magnetic field

Consider a loop of wire in a uniform magnetic field. The field is perpendicular to the plane of the loop, such that the magnetic field lines pass through the loop. We will examine the interactions of the loop with the B field and the resulting induced EMF. Which of the following statements are true about this case? (1) if t

### Electro Magnetic Induction: Motional EMF in a satellite

A natural satellite whose diameter is 10^4 meters moves at velocity of 1 km/s in the direction normal to the magnetic field of a planet in a region where B=10^-7 tesla. The satellite has appreciable conductivity. A) The satellite moves in a perfect vacuum. What happens? B) The ambient gas has a density of the order

### Electro Magnetic Induction: EMF Induced due to Shape Change

An emf is induced in a conducting loop of wire 1.24 m long as its shape is changed from square to circular. Calculate the average magnitude of the induced emf if the change in shape occurs in 4.03s, and the local 0.109 T magnetic field is perpendicular to the plane of the loop. Please solve and explain problem.

### Determining Current and Production of Thermal Energy

Part 1: A 32.1 cm diameter coil consists of 15 turns of circular copper wire 1.70 mm in diameter. A uniform magnetic field, perpendicular to the plane of the coil, changes at a rate of 8.70E-3 T/s. Determine the current in the loop. Part 2: Determine the rate at which thermal energy is produced. Please solve and exp