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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.

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

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,

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

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

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

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

Elements of Crystallizes in Body-Centered Cubic Lattice

Chapter 11 5. An element crystallizes in a body-centered cubic lattice. The edge of the unit cell is 2.98 , and the density of the crystal is 8.99 . Calculate the atomic weight of the element. 9. Calculate the minimum number of grams of propane, , that must be combusted to provide the energy necessary to convert 5.70

Equations for Currents, Loops, and Torques

What equations are needed to solve this problem? How would the equations change if it was a circular loop? a) A square loop of the side length (a) carries a current (i) in the clockwise direction. The loop is placed in a magnetic field at an angle of 45 degrees to it (you can rotate the loop about the field as you like to ma

3 questions on electric circuits with many components

1.) What is the potential difference Vad in the circuit of the figure? (Part A 1 figure) 2.) What is the terminal voltage of the 4.00-V battery? 3.)A battery with emf 10.30V and internal resistance 0.50ohms is inserted in the circuit at d, with its negative terminal connected to the negative terminal of the 8.00-V batt

Set of multiple choice questions on magnetic fields.

2. A coil of wire carries current I flowing clockwise as shown in the figure. The outer circle is the current loop. If the observer could "see" the magnetic field inside this arrangement of loops, how would it appear? (see attached file for diagrams) 3. A conducting loop of wire is placed in a magnetic field that is norm

Magnetic force of a current carrying cross bar placed in a magnetic field. To determine instantaneous magnitude of acceleration, steady state speed and current flowing through it.

A schematic 'rail gun motor' is shown in figure 1 (see attachment). Two horizontal parallel rails are a distance L apart and are joined at one end by a voltage source producing a fixed voltage Vo. A crossbar of mass m completes the circuit. The cross bar is free to slide on the rails, always remaining perpendicular to them. All

Given a circuit and find dissipated as thermal energy in the battery.

1. A wire of resistance 5.0 ohm is connected to a battery whose emf is 2.0V and whose potential resistance is 1.0 ohm. In 2.0min, how much energy is (a) transferred from chemical form in the battery, (b) dissipated as thermal energy in the wire, and (c) dissipated as thermal energy in the battery? 2.The starting motor of a ca

Thevenin's Theorem

a. Use Thevenin's theorem to calculate an equivalent e.m.f and resistance for the circuit contained in the box to the left of terminals A and B (steady state conditions) b. Sketch the complete Thevenin circuit plus load and calculate the current through the 10 resistor.

Electromagnetic induction and the Lorentz force

1. An infinitely long, straight wire carries a constant current I along the z-axis. A rectangular loop of conducting wire (dimensions = a x b) is located in a radical plane at a distance x from the wire, as shown. (see the attached file for the diagram) (a) Find the flux of the magnetic-field B through the loop. (b) If

Batteries and Hydrogen

1. The lead acid battery used in cars uses the reaction of Pb + PbO2 + 2H+ + 2HSO4- ---> 2PbSO4 + 2H2O and has a cell potential of 2.046 volts. How are 6 volt and 12 volt batteries produced for cars? a. The pH is made very acidic. b. 3 or 6 cells are connected together to increase the voltage c. The concentrati

Introduction to Decision Making

You are observing a meeting between Milhouse (one of your co-workers) and a salesman who is trying to sell an additional part to a machine that your company recently purchased. The salesman is well into his routine, and has already gotten your co-worker to admit that a quality product is of utmost importance to the future of the

Looking for help with image formats

What kinds of image formats are available for putting onto the Internet? What different file formats that are available to me? What are the major advantages and disadvantages of each one?

Induced emf in loop.

The current in the long straight wire AB of the figure is upward and is increasing steadily at a rate of di/dt. 1. what is the total flux in through the loop? 2. what is the induced emf in the loop?

Induced EMF in a circular loop

A circular loop of flexible iron wire has an initial circumference of 165.0 cm, but its circumference is decreasing at a constant rate of 12.0 cm/s due to a tangential pull on the wire. The loop is in a constant uniform magnetic field of magnitude 0.500 T, which is oriented perpendicular to the plane of the loop. Find the in

EMF induced in a conductor moving in a magnetic field.

EMF in a Bullet. At the equator, the earth's magnetic field is approximately horizontal and is directed toward the north and has a value of X. Part A Estimate the emf induced between the top and bottom of a bullet shot horizontally at a target on the equator if the bullet is shot toward the east. Assume the bullet has a len

Current as a Function of Time for a Circuit

Let us now consider a different RC circuit. This time, the capacitor is initially charged (q(t) = q_0), and there is no source of EMF in the circuit. We will assume that the top plate of the capacitor initially holds positive charge. For this circuit, Kirchoff's loop rule gives IR + q/C = 0, or IR = -q/C. Find the current

Time for capacitor charge to reach 99.9% maximum

Consider a series circuit containing a resistor of resistance R and a capacitor of capacitance C connected to a source of EMF E with negligible internal resistance. The wires are also assumed to have zero resistance. Initially, the switch is open and the capacitor discharged. Let us try to understand the processes that take