EMF measurements are measurements of ambient (surrounding) electromagnetic fields that are performed using particular sensors or probes, such as EMF meters. These probes can be generally considered as antennas although with different characteristics. In fact, probes should not perturb the electromagnetic field and must prevent coupling and reflection as much as possible in order to obtain precise results. There are two main types of EMF measurements:
broadband measurements: performed using a broadband probe, that is a device which senses any signal across a wide range of frequencies and is usually made with three independent diode detectors;
frequency selective measurements: in which the measurement system consists of a field antenna and a frequency selective receiver or spectrum analyzer allowing to monitor the frequency range of interest.EMF probes may respond to fields only on one axis, or may be tri-axial, showing components of the field in three directions at once. Amplified, active, probes can improve measurement precision and sensitivity but their active components may limit their speed of response.
Hello.
One doubt.
How is the distance between the charged particles and the EMF between them get balanced out? That is, if I have a proton and electron, they attract each other, move towards each other and form a H atom. But going by this attractive force, they should approach each other...
Hello.
> Is there any electromagnetic force of repulsion between two quarks?
> And, hypothetically speaking [as independent quarks are not observable], could there be EMF of attraction between an electron and an independent quark?
Actually, both the questions boil down to the following -...
I read this topic in many books but i really can't figure out what really the difference is!
Please someone help me out!
One of the book differentiated them as follows ...
emf is the work done by the battery force (Fb) in moving unit charge from one electrode to another.
emf is due...
Hello.
Down below I have listed few questions. I think all of them deal with the same confusion/doubt that I have about EM force [that is why I have clubbed them in one post].
Because of the basic confusions/doubts, I might not have framed the questions clearly. Please correct where ever I...
Homework Statement
This problem arises from a much larger essay/lab/project thing. I know that there is an induced current in the wire of an AC electromagnet because the magnetic field is constantly changing along with the AC current, so it makes sense to me that will produce a constantly...
Hey, I'm trying to find a suitable diode to protect against some back EMF in my circuit, but I don't know much about them and so I'm having a really hard time finding one. If someone could look at what i need and then possibly send me a link i'd be so grateful.
Requirements:
back EMF = 137mV...
Homework Statement
A square loop of side .45 m is placed in a region where there is a magnetic field of strength 8T directed perpendicularly out of the plane of the loop. If the magnetic field is increased to 14 T in .03 seconds, calculate the average emf induced in the loop
Homework...
Suppose now i have connected a solenoid with a dc power supply of 10V
When i increase the voltage to 20V the magnetic flux through the coil have increased
will emf be induced shortly to oppose the change?
what if i now change it to a 10V ac power supply
so will there always be induced emf...
If the Earth's magnetic field as measured on the surface of the Earth is somewhere between .3 and .6G and cell phone doses are around 2mG, is it then absurd to be at all concerned with even heavy exposures to the kind of low grade doses that cell phones and other electrical devices produce?
I...
Hi.
Could you please give me a description/analyse a variety of flux changes that can be used to produce an emf.
Could you confirm what is flux and emf in this situation?
Homework Statement
A bar of mass m, length d, and resistance R slides without friction in a horizontal plane, moving on parallel rails. A battery that maintains a constant emf \epsilon is connected between the rails, and a constant magnetic field B is directed perpendicularly to the plane...
Homework Statement
What is the average emf created by a 15 turn cable that is .5 meters in diameter, lies flat with the surface of the Earth and is flipped 180 degrees in 2 seconds?
*Assume the Earth produces a magnetic field of .5 micro Tesla.
Homework Equations
e=-n*r^2*delta...
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) = (15.0 A)sin(2500t) where t is in seconds. The distance a is 12.0 cm, and b is 15.0 cm.
Homework Equations
In the question...
Homework Statement
Figure below shows two circular regions R1 and R2 with radii r1 = 21.7 cm and r2 = 30.5 cm. In R1 there is a uniform magnetic field of magnitude B1 = 51.3 mT directed into the page, and in R2 there is a uniform magnetic field of magnitude B2 = 75.7 mT directed out of the...
Homework Statement
A simple generator has a coil with dimensions 1.0 cm x 1.0 cm which
is rotated at 60 Hz in 1.0 T magnetic field. How many windings (turns of
wire) are needed to generate a peak emf of 120 Volts ?
Homework Equations
1. emf E = - d (magnetic flux) / dt
2. magnetic flux = (B...
I'm relatively new here, but I felt that you guys might be able to help me.
I'm trying to design a directed electromagnetic field generator with a variable field strength and oscillation rate.
What I'd really like to know is exactly how difficult would this be?
My EE experience is rather...
Homework Statement
[PLAIN]http://img220.imageshack.us/img220/2589/44045733.png
Semicircular wire MN of diameter L moves with speed v perpendicularly through a uniform magnetic field of strength B.
1. Find the magnitude of the induced emf generated between M and N.
2. State whether M...
Sometimes when i swipe my card at walmart it doesn't read it , And the guy was like let's put it a plastic bag and then try it, and it works and I've heard a couple of other people doing this.
So when i slide my card the magnetic strip induces a voltage and reads the card. So why does...
In power plants alternating emf is generated by rotating loop in magnetic field which is directly proportional to angular velocity of turbine.I think it is highly impossible to maintain angular velocity of turbine constant(especially in hydro power plants).Then how are they supplying a...
Homework Statement
Describe with the aid of diagrams how the back emf and induced current vary in a single-coil DC motor over one full rotation of the armature.
Give particular attention to the rate of change of flux in the coil and to the direction(s) of the DC and induced current...
Part A
Find the emf E1 in the circuit of the figure .
=
Part B
Find the emf E2 in the circuit of the figure.
=
Part C
Find the potential difference of point A relative to point B.
A) I wrote a KVL using the top loop. First I found out what the current...
Hi!
I'm trying to fully grasp why the potential drops when an internal resistance is present in a source of emf. At first I thought that yes it would be harder to "push" the charges to the higher potential, but once there, why shouldn't the higher potential be the same as before? Just as if a...
Homework Statement
coils rotating in a magnetic field are often used to measure unknown magnetic fields. As an example, consider a coil of diameter 2.00 cm with 72.0 turns that is rotated about an axis perpendicular to the field at a rate of 20.0 Hz. If the maximum induced emf in the coil is...
I have always wondered if anyone has ever developed an understanding of why Back EMF happens?
All I know is it happens when the the field inside of a transformer collapses at some low frequency during the collapse of the coil when the transistor shuts off creates a huge spike hundreds of...
First of all this isn't really Homework problem, but since it is based on homework problem, I'll post on this section of the forum. Feel free to move if I was supposed to post on different part of the forum.
Either way, I'll use homework as an example since that is what brought this up...
Homework Statement
"From your graph, calculate the EMF and internal resistance of your cells. Include uncertainties in your calculations"
Now I know how to work out the emf and int. resistance, but I am just not sure about how to incorporate uncertainties.
Homework Equations
y = mx +...
Homework Statement
A generator has a 170-turn square coil, 5 cm on a side.
Find the peak emf in this coil when it's rotating at 90.0 Hz in Earth's field, 5*10^-5 T
Express your answer to one significant figure and include the appropriate units.
Homework Equations
Emf = NBAw
The...
Let us consider a rectangular plate moving horizontally in a vertical magnetic field with its length perpendicular to its direction of motion.This may be closely approximated by the wing of a flying aircraft.The axial emf is given by the traditional formula, E=BLV.
Now when the...
Homework Statement
The positive terminals of two batteries with emf’s of E1 and E2, respectively, are connected together. Here E2 > E1. The circuit is completed by connecting the negative terminals. If each battery has an internal resistance r, the rate with which electrical energy is...
Any help appreciated with these!
Homework Statement
1. A battery is made up from a series combination of six 1.2 volt nickel cadmium cells supplying a 10ohm load-
a) What is the open circuit voltage?
b) Ignoring internal resistance, what is the current flowing in each cell?
2. The nickel...
Electromotive force is usually defined as the work done in transporting a unit positive charge in a round trip in the circuit. That is,
EMF= loop integral of E.dL
Now let us examine the above statements in the light of a constant source of emf driving a steady current in the circuit.
If the...
Homework Statement
The question itself doesn't make sense to me, it says to find emf but the answer box has V=
?
problem is an attachment.
Homework Equations
I=e/(r+R)
Ir+IR=emf
P=VI
The Attempt at a Solution
If it wants voltage that's simple P=I^2R P=V^2/R V=54.8V if...
Homework Statement
An infinite cylinder (radius a) with a uniform volume charge density rho_v is given. The axis of the cylinder coincides with the z axis. The following magnetic field exists:
B=B0cos(wt+a) for r<=a (i.e., inside the cylinder and on its walls)
B=0 for r>a...
Hi there,
For an assignment at school I chosen to investigate EMF. I have chosen to focus my investigation around cabling at concerts in an attempt to answer the question: How does the EMF generated by cabling affect each other. I have done some research and found that if cables are run at...
Homework Statement
What is the emf of the galvanic cell
Al(s)[Al+3(aq .18mol/liter) [] Fe+2(aq .85mol/liter)[Fe(s)
Homework Equations
The Attempt at a Solution
Al(s) ---> Al+3 + 3e E=-1.676 V
Fe+2 + 2e ---> Fe(s) E=-.440V
How do we proceed after this...
Homework Statement
A battery supplies a steady current of 5.6 A for 21 s. During this time 1410 J of chemical energy is transformed into electric energy, but 560 J of this electric energy is transformed into heat energy inside the battery. What is the total power output of the battery...
Homework Statement
C
alculate the emf (in volts) induced in a loop of wire if the magnetic flux in the loop increases from zero to 71.1 milliweber in 16.7 millisec.
Homework Equations
faradays Law
The Attempt at a Solution
The only law I know is faradays law which uses Area...
Homework Statement
There is a Static magnetic field,with its intensity B. Assume a coil moving
in the magnetic field, with its position function y=asinwt. then calculate the voltage of U
Homework Equations
The Attempt at a Solution
Homework Statement
A square of side 2cm, in the first quadrant of the x-y plane, with a corner at the origin, is in a magnetic field pointing out of the page of magnitude 4t2y.
Calculate the emf around the square at t = 2.5s and give its direction.Homework Equations
\epsilon = - \frac{d}{dt}...
Homework Statement
A flat coil of wire consisting of 20 turns, each with an area of 50 cm^2 is positioned so that the normal to its plane is at the angle of 30 degrees to a uniform magnetic field that increases its magnitude at a constant rate from 2.0T to 8.0T in 2.0 s.
Homework Equations...
Consider a rotating disk on a uniform magnetic field. Faraday's law states that
\epsilon = - \frac{d\phi}{dt}
In this situation, \vec B is constant and the area of the disk is constant. Hence, the magnetic flux is constant and there should be no emf. What am I missing?
Homework Statement
A 25-turn circular loop of wire has a diameter of 1m. In 0.2 seconds it is flipped 180 degrees at a location where the magnitude of the Earth's magnetic field is 50 micro T. What is the emf generated in the loop?Homework Equations
-(dB/dt)(A)=VThe Attempt at a Solution
When I...
Question:
A voltaic cell is constructed with two silver-silver chloride electrodes, each of which is based on the following half-reaction: AgCl(s) + e- = Ag(s) + Cl-(aq). The two cell compartments have [Cl-]= 1.41×10−2 M and [Cl-]= 2.70 M, respectively. What is the emf of the cell for the...
1. How fast would you have to drive your car to create a 3.0 V motional emf along your 1.2 m-long radio antenna? Assume that the motion of the antenna is perpendicular to B.
2. d(phi)/dt = EMF
dphi = B*A
v = dx/dt
3. I'm really not sure here. I think the length of the antenna...
1. A 100-turn, 2.0-cm-diameter coil is at rest in a horizontal plane. A uniform magnetic field 60 degrees away from vertical increases from 0.50 T to 1.50 T in 0.60 s.
2. EMF = N*d(phi)/dt
phi = flux = ABcos(theta)
3. dB/dt = 1/0.6
EMF = 1000*(1/0.6)*pi*r2*0.5 = 0.262 V
Is...
Homework Statement
A solenoid with a length of 25.0 cm, radius 1.60 cm and 5500 turns carries a current of 1.50 A. A small coil of radius 1.05 cm and 130 turns is placed at the center of the solenoid with its axis in the same direction as that of the solenoid. A 470 ohms resistor is connected...
Here is how the question is stated exactly:
A circular conducting loop is held fixed in a uniform magnetic field thatt varies in time according to B(t) = B0exp(-at) where t is in s, a is in s-1 and B is the field strength in T at t=0. At t=0, the emf induced in the loop is 0.0758 V. At t=...
Hai - I am revising and now I am confused - equations for both electromotive force (emf) and energy begin E=... (in different sections of my electricity notes)
Does that mean EMF is a type of energy or am I missing something?
Thanks :)
Homework Statement
A current of 22 amperes flows in a heater coil whose resistance is 5 ohms. What E M F in volts is required?
Homework Equations
The Attempt at a Solution
Not quite sure where to begin. I'm thinking the internal resistance, R, is inherent w/the circuit so EMF...