Emf Definition and 901 Threads

hmm just a topic for discussion..im revising for an exam and i found an old paper asking to find rms values of electric field and magnetic field from power...and that's easy, using the poynting vector. Then it asks, given a piece of wire of length l in these fields, you can either use it as a...

Homework Statement A coil of 15 turns and radius 10cm surrounds a long solenoid of radius 2cm and 1x10^3 turns/m. The current in the solenoid changes as I = (5A)sin(120t). Find the induced emf in the 15-turn coil as a function of time. Homework Equations emf = -Nd[flux]/dt d[flux]...

A 11.8m long steel beam is accidentally dropped by a construction crane from a height of 8.62m. The horizontal component of the Earth's magnetic field over the region is 16.7μT. What is the induced emf in the beam just before impact with the Earth, assuming its long dimension remains in a...

Homework Statement A rectangular loop of wire has area A. It is placed perpendicular to a uniform magnetic field B and then spun around one of its sides at frequency f. The maximum induced emf is: BAf BAf 4(pi)BAf 2(pi)BAf 2BAf Note: No, it's not my mistake that BAf appears...

Homework Statement In Figure 30-52 (see attached), a metal rod is forced to move with constant velocity v along two parallel metal rails, connected with a strip of metal at one end. A magnetic field B = 0.370 T points out of the page. (a) If the rails are separated by 26.0 cm and the...

A circular conducting coil with radius 2.61 cm is placed in a uniform magnetic field of 0.827 T with the plane of the coil perpendicular to the magnetic field. The coil is rotated 180° about the axis in 0.222 s. (a) What is the average induced emf in the coil during this rotation? (b) If the...

Homework Statement http://www.jyu.fi/kastdk/olympiads/2005/Th2.pdf http://www.jyu.fi/kastdk/olympiads/2005/Th2%20Solution.pdf (Question 3) My first doubt is why the magnetic field at the center of the coil is: |\vec B|=\frac{\mu_0 NI}{2a} and not |\vec B|=\mu_0 nI, where n=N/l...

Homework Statement A car with a vertical radio antenna 85cm long drives due east 25 m/s. The Earth's magnetic field at this location has a magnitude of 5.9 * 10-5 T and points northward, 72 degrees below the horizontal. a) Is the top or the bottom of the antenna at the higher potential? b)...

Homework Statement A wire of resistance 5.0 Ω is connected to a battery whose emf ε is 2.0 V and whose internal resistance is 1.0 Ω. In 2.0 min, how much energy is (a) transferred from chemical to electrical form in the battery, (b) dissipated as thermal energy in the wire, and (c)...

Homework Statement Assume the field inside the larger coil (.075m Radius, 1200 loops), reaches the maximum value when the smaller solenoid, (.05m radius, 1200 loops), is halfway inserted. with what constant velocity must the smaller solenoid be inserted to induce 2.3V in the larger solenoid...

Homework Statement The 2-cm (radius) current loop shown in the figure is changing from θ1 = 11 degrees to θ2 = 66 degrees in a magnetic field 2 T in 0.5 seconds. What is the magnitude of the induced emf to the nearest hundredth of a millivolt. The wire in Problem 2 has a thickness of 1.04...

Induced EMF and Current in a Shrinking Loop Homework Statement Shrinking Loop. A circular loop of flexible iron wire has an initial circumference of 170 cm, but its circumference is decreasing at a constant rate of 13.0 cm/s due to a tangential pull on the wire. The loop is in a constant...

Homework Statement A car with a vertical radio antenna 75 cm long drives due west at 23 m/s. The Earth's magnetic field at this location has a magnitude of 5.9 10-5 T and points northward, 74° below the horizontal. Find the induced emf between the ends of the antenna. Homework Equations...

A car with a vertical radio antenna 75 cm long drives due east at 29 m/s. The Earth's magnetic field at this location has a magnitude of 5.9* 10^-5 T and points northward, 72° below the horizontal. (b) Find the induced emf between the ends of the antenna. Relevant Equations: E = BVL...

Homework Statement The armature of an AC generator is rotating at a constant speed of 30 revolutions/second in a horizontal field of flux density 1.0Wb/m^2. The diameter of the cylindrical armature is 24cm and its length is 40cm. What is the maximum emf induced in the armature having 30 turns...

Hello All, My question concerns induced emf in an air-core toroid setup. This is simply a thought experiment and I think I know the answer to this but thought I would run it past you all anyway. Picture a non-magnetic toroidal core with two one-layer coils wound on it 180 degrees apart...

Homework Statement The magnetic field perpendicular to a circular loop of wire 23 cm in diameter is changed from +0.52 T to -0.45 T in 175 ms, where + means the field points away from an observer and - toward the observer. Homework Equations (pardon me with the equations, I am LaTeX...

Can i get some help with this homework problem?? A physicist wraps a long copper wire around a toilet paper roll and places the roll in a uniform magnetic field. The axis of the roll is aligned with the field. The radius of the roll is r = 6 cm and the strength of the field is B = 0.1 T. If the...

induced emf! Hello, I am studying magnetic induction, induced emf, and faraday's law, that sort of thing. My book gives an example where the magnitude of a B-field is increasing at constant rate through an axis of a circular coil with N number of turns and a certain radius r, find the...

I have a homework problem where there is a long copper wire around a toilet paper roll that is placed in a uniform magnetic field. The axis of the roll is aligned with the field. I am given the radius of the roll, strength of the field, and a velocity at which the wire is unrolled. How do i...

http://www.electronics-lab.com/projects/science/006/emmeter.gif" i want to ask 1. is it used to detect emf ? is it an emf meter 2. how to detect 3. how does am-plifer work ? transistor used for?? diode use for? 4 if i change other value of capacitor? inductor? resistor...

To find the emf generated by two ten turn coils, the planes of which are at 60 degrees in a radial magnetic field B=Bcos(theta)sin(omega*t) in the direction Ar, that rotates with omega rad/sec at the instant when the coil A1A2 makes an angle alpha with the plane of the maximum flux density...

Hey. At school, we are currently studying electricity, and i am having some trouble understanding some of the concepts. From what i understand, EMF is the energy given to each unit of charge, which allows it to flow around a circuit. Why do the charges need energy? Is the energy they receive...

An emf self-induced in a solenoid of inductance L changes in time as E=E_0e^(-kt) Find the total charge that passes through the solenoid, if the charge is finite. (Use E_0 for 0, k, and L as necessary.) Now I know that the induced emf is E_L=-L(dI/dt) I'm having a hard time on this...

In a physics laboratory experiment, a coil with 210 turns enclosing an area of 12.7 cm^2 is rotated during the time interval 3.70 \cdot 10^{−2} sfrom a position in which its plane is perpendicular to Earth's magnetic field to one in which its plane is parallel to the field. The magnitude of...

Hello, I was just wondering if someone could explain to me why there is a huge spike of current & voltage in a wire when you close and open an electrical circuit. I've noticed these 'kicks' or 'spikes' in wires when runing square waves through them (doesn't seem to occur with sine waves). I...

I'm doing a few practicals at home this summer, and the one that is bugging me is about EMF. I have measured voltage and current at different resistances across a 4,5 V battery, and made a graph. But to find the emf, am I supposed to take the slope of the graph, or the gradient? Or is that the...

A piece of copper wire is formed into a single circular loop of radius 9 cm. A magnetic field is oriented parallel to the normal to the loop, and it increases from 0 to 0.45 T in a time of 0.45 s. The wire has a resistance per unit length of 3.3 10-2 /m. What is the average electrical energy...

average emf is it same as induced emf?? Q: a 25-turn circular coil of wire has diameter 1.00m. it is placed with its axis along the direction of the earth'smagneticfield of 50.o uT, and then in 0.200s it is flipped 180 degrees. an average emf of what magnitude is generated in the coil? N =...

Hello Iam stuck on a topic (have been for a while !) about the electro motive force around a circuit (emf). Iam also confused about how internal resistance plays a role in this. I do vaguely remember a teacher telling me that max current is at max internal resistance (or something around...

This problem is difficult to describe, so I'll post a picture. http://img71.imageshack.us/my.php?image=pic1ik.gif The figure above shows a rod of length L caused to move at a constant speed v along horizontal conducting rails. The magnetic field B (the magnitude and direction of which are...

Hey lads, if anyone can, please check If I am correct... Thanks :) [i]A 100 turn circular coil has a diameter of 2 cm and a resistance of 50 Ohms. The plane of the coil is perpendicular to a uniform magnetic field of magnitude 1 T. The direction of the field is suddenly reversed. (a) Find...

A 1 m long large coil with a radius of 15.2 cm and 280 turns surrounds a 7.6 m long solenoid with a radius of 5.2 cm and 3200 turns. The current in the solenoid changes as I=I_0 sin (2\pi f t) where I_0= 30 A and f=60 Hz.Inside solenoid has 3200 turns and outside coil has 3200 turns. The...

A 5.97 m long steel beam is accidentally dropped by a construction crane from a height of 6.82 m. The horizontal component of the Earth's magnetic field over the region is 12.2 \mu T. The acceleration of gravity is 9.8 m/s^2. What is the induced emf in the beam just before impact with the Earth...

These circuit questions seem to give me so many problems, this question in particular. What are the emf and internal resistance of the battery in the figure below? I have the answers, that emf is 9V and internal resistance is 0.5 ohms, however I'm having problems getting there. What...

Doin a question based around RC circuits and was in a bit of a bind, lookin for some help. The capacitor in the figure below begins to charge after the switch closes at t = 0s. a) what is deltaVc when t >> 0 after switch is closed? b) what is Qmax in terms of emf, R and C? c) in this...

A magnetic field with the time dependence shown in Figure 23-38 is at right angles to a 181 turn circular coil with a diameter of 3.91 cm. What is the induced emf in the coil at each of the following times? (a) t = 2.50 ms 0 V (b) t = 7.50 ms (c) t = 15.0 ms...

Here is the question i am working on: An AM radio station broadcasts with average power 4000 W in all directions. A dipole receiving antenna 65 cm long is at a location 4 miles from the transmitter. Compute the amplitude of the emp that is induced be this signal between the ends of the...

What would be the change of the induced emf in the secondary coil of a two coil system ( without ferromagnetic core ) if both the amplitude and the frequency of the current in the primary coil would double?: emf would stay the same emf would be halved emf would be 4 times larger...

emf, current, electric fields...what direction is everything moving? This is a very simple question but I can't seem to figure out the actual direction that things are moving in a simple circuit. Suppose you have a simple circuit consisting of a battery and a resistor: The electrons inside the...

1] A square loop of wire, with sides of length 'a' lies in the first quadrant of the xy-plane, with one corner at the origin. In this region there is a non-uniform time-dependent magnetic field \vec B (y,t) = ky^3t^2\hat z. Find the induced emf in the loop.I applied the flux rule here...

If we have a loop with radius 12 cm that lies in a uniform magnetic field of 1.5T. The magnetic field is in the positive z direction and the loop lies in the horizontal xy-plane. Now if the loop is removed from the field in a time interval of 2.0x10^-3 s what will the average induced emf be...

I'm reposting this because my homework is due in an hour and I still have not received help on how to solve this. I understand now that the the loop is equal to one. But could someone be generous enough to explain to me what the area is on problem 2 and 3 and why .503 is wrong for question 1...

I'm having a lot of trouble with the following questions. I was wondering if someone could steer me in the right direction and tell me what I'm doing wrong. I suppose my biggest problem is I don't understand how to do these without knowing the number of turns in the coil. Here's what I've done...

A 20 H inductor carries a steady current of 4.0 A. At what rate must the current be changed to produce a 40 V emf in the inductor? I odn't get this one because it gives you all the information! The formula is: EMF = -L di/dt they want u to find di/dt, but they already give you it has a steady...

An elastic conducting material is stretched into a circular loop of 11.0 cm radius. It is placed with its plane perpendicular to a uniform 0.900 T magnetic field. When released, the radius of the loop starts to shrink at an instantaneous rate of 80.0 cm/s. What emf is induced in the loop at that...

Hello everyone, I'm confused on how to do this problem, it says: An electric generator contains a coil of 120 turns of wire formed into a rectangular loop 40.0 cm by 20.0 cm, placed entirely in a uniform magnetic field with magnitude B = 3.50 T and with B initially perpendicular to the coil's...

" A circular loop of wire 10 cm in diameter is placed with its normal making an angle of 30 degrees with the direction of a uniform 0.50T magnetic field. The loop is "wobbled" so that its normal rotates in a cone about the field direction at the constant rate of 100rev/min; the angle between the...

Hi, My Question: What is the inductance of a coil if the coil produces an emf of 2.50V when the current in it changes form -28.0 mA to 31.0 mA in 12.0 ms? For this I know I will need to use this equation: E=-M(delta I)/(delta t) My problem is that I was wondering if coming up...

Hey, I got this question in a homework from a teacher of mine: "A car battery with a 15.0 V emf and an internal resistance of 0.0430 is being charged with a current of 62.5 A. What is the potential difference across its terminals?" I've tried nearly every formula I know on it. EMF =...