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.
Hi,
What if the inductor coil is wound one way rather than the other. Then the circular flow of current will be clockwise in one case and anticlockwise in the other.
And if the inductor is connected to an ac source, then the current will vary.
Now in both the orientations, the variation...
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suppose we have a coil sitting on a desk (with radius =1), and then a spark passes by the side of it, in such a way that the magnetic flux through the coil is maximized. The coil is attached to a full wave rectifier which is connected to a very large capacitor.
There is an...
I'm doing a lab write-up for physics 2. The experiment is about the title, a bar magnet being dropped through a solenoid.
I have to explain four graphs that plot the change in emf (y axis) vs. time (x) axis. There are incoming and outgoing peaks on these graphs. I have to tie these results...
I'm doing a lab write-up for physics 2. The experiment is about the title, a bar magnet being dropped through a solenoid.
I have to explain four graphs that plot the change in emf (y axis) vs. time (x) axis. There are incoming and outgoing peaks on these graphs. I have to tie these results...
Hi everyone,
This question is bothering me for days and would hope to receive some help in this forum. This question is with regards to Faraday's law on EMI.
Will an emf be induced when a copper rod is accelerated between a uniform magnetic field?
My answer would be no if the rod has...
Hi all,
I've been using Faraday's law to find the EMF in a coil of wire in a changing magnetic field.
EMF = -N (change in mag flux/change in time) for N loops
I'm finding that the EMF is always positive regardless of whether the change in flux is positive or negative. I'm wondering at...
Homework Statement
In the figure below, a circular loop of wire 12 cm in diameter (seen edge on) is placed with its normal at an angle θ = 30° with the direction of a uniform magnetic field B of magnitude 0.60 T. The loop is then rotated so that N rotates in a cone about the field direction...
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A square wire loop of dimensions L X L (L = 15.5 cm) oriented in the xy-plane and centered on the x-axis enters a region where the magnetic field (B = 0.855 T) is first oriented in the +z- and then in the -z-direction as shown in the diagram below. (Note: W = 15.501 cm and...
According to Faraday's laws... change in magnetic flux linking a coil induces current in the coil.., but for conduction of electrons ...there must be an electric field ! how is the electric field induced in the coil??
Homework Statement
"You push a rectangular loop of width .2m, length .8 m, and resistance R=200\Omega into a magnetic field (out of page) Bout=.4 T and a speed v=.2 m/s. The long side of the rectangle is parallel to the x axis. What is the current flowing in the loop?"
Homework Equations
I...
I've been going through some materials, and I was reading about electric circuits. From what I read I figured that the electric current is dictated by the current source, and it's preserved(in the respectable branches) by the emf. Is that right? Or my feeling that I'm way off is true :)
Homework Statement
Find the induced emf in a rotating disc of radius (a) in a magnetic field (B), rotating with uniform angular velocity (w). If the disc is replaced by a rotating conductor of length (a) fixed at one end find the induced emf in the conductor.
2. The attempt at a solution...
Hi
I have a practical problem/question:
I need to wire 2 PLC-s for communications (RS485 signal) and I am planning to use shielded twisted pair cable (Cat5 FTP). The signal cables are quite short - approx. 6 m.
One possible problem that could arise: between the 2 PLC-s, there is a...
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A circular coil of area A with N turns rotates at an angular velocity w about an axis perpendicular to its own axis and to a uniform magnetic field B. Find an expression for the induced EMF in the coil in terms of B, N, A, w and time t. What is the orientation of the coil...
I know the equation for emf: -dflux/dt= -dB/dt*A . In my case everything is constant accept the magnetic field and I am unable to find the equation for that. I know that is what dB is for but that simply does not work in this case.
What is the equation for induced voltage, when everything is...
Homework Statement
Consider a circular loop with resistance R. Perpendicular to the loop there is a magnetic field
B(t) = t, where t is the time. If a voltmeter is connected to two points on the loop separated
by 90 degrees, what would it show?
The Attempt at a Solution
the answer...
Homework Statement
What is the emf E of the battery at the lower left in the figure? Answer in units of V.
http://img508.imageshack.us/img508/6/82852928.png
Can someone guide me? I'm confused as to where to start. I think I am supposed go the route of the loop, but I am given the...
Homework Statement
A wire of resistance 11 ohms and length 2.3 m is bent into a circle and is concentric with a solenoid in which the magnetic flux changes from 8 T·m2 to 6 T·m2 in 0.2 seconds.
a) What is the emf in the wire?
b) What is the non-Coulomb electric field in the wire?
c)...
i am wondering why in some problem they are regarding back emf of a motor as a constant value that characterizes the motor although current is sometimes variable? i guess the reason is for simplifying the problem, what do u think? can this occur in reality?
thanks for helping.
Sorry, the title is wrong. Should be "magnetic flux" of a single loop wire around a solenoid.
Homework Statement
A solenoid 4 cm in diameter and 20 cm in length has 250 turns and carries a current of 15 A. It is surrounded by a loop of wire 10 cm in diameter. The loop is positioned...
while solving an exercise, i have found that they are considering the back emf of a motor constant although the current is not constant? how comes that? shouldn't it be variable as current varies?
they are considering that as E=Ir+E' where E' and r are constants?
Homework Statement
determine the terminal voltage in each battery.
Emf1=18V
r1=1 ohm
EMF2=12V
r2=2 ohm
R=6.6 ohms
also the batterys currents are opposing each other.
Homework Equations Vab=emf-Ir
The Attempt at a Solution i used kirchnoffs rule to find the current I ...
Homework Statement
http://img854.imageshack.us/img854/3980/33288207.th.png
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The Attempt at a Solution
http://img813.imageshack.us/img813/1065/60582408.th.png
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\varepsilon = IR
\varepsilon = -\frac{d \Phi}{dt}...
Homework Statement
Why is the following situation impossible? A battery has an emf of E = 9.2V and an internal resistance of r = 1.2 ohms. A resistance R is connected across the battery and extracts from it a power of P = 21.2W.
Homework Equations
My book gives these equations throughout the...
Homework Statement
Hey guys,
This is just a qualitative question.
So assume I have a massive super large magnetic field, and pull a straight, isolated conducting wire sideways through it with constant velocity. I know that the EMF induced is given by
emf = Blv where
l is the length of the...
1-this is what is written in my book:
E= Ir+E' where E' is the back emf, r and E' are constants
P(mechanical)=E'*I
an electrical motor functions only if the generator connected across its terminals delivers a positive potential difference that exceeds its back emf.
So my question is, why are...
Homework Statement
We have seen this week that there are 3 ways to generate an emf (voltage or a current) using Faraday's law. Suppose you have a permanent magnet (of your choice), and 5-cm radius coil of wire with 100 loops, and a sledge hammer. Describe the three different ways the loop of...
1. In the figure the square loop of wire has sides of length 2 cm. A magnetic field points out of the page; its magnitude is given by
B = 4.0 t^2y
where B is in teslas, t is in seconds and y is in meters. Determine the emf around the square at t = 1.50 s...
Hey Folks. I am currently designing a buggy which tracks an inductive wire using two inductor sensors. The wire is carrying 20Vac pk-pk , 125ma at 10kHz. I have designed a sensor circuit which has a ratio of 2:1 ie it outputs a waveform of 10Vac pk-pk (assuming 100% mutual inductance). This is...
I don't know English well(I'm from russian speaking countries) but I try to explain the problem(and practise my english too)
Homework Statement
Transfrom scheme into eq. scheme with one EMF and one resistor.
Homework Equations
Where is the series configuration of resistors and where is...
Homework Statement
A cell is connected to a 10.0 Ohm resistor. The pd across the 10.0 Ohm resistor is 10.43 V.
A 4.00 Ohm resistor is connected in parallel with the 10.0 Ohm resistor. The pd across the 10.0 Ohm resistor falls to 7.87 V.
Calculate the emf and the internal resistance of the...
Homework Statement
A conducting loop is made in the form of two squares of sides s1 = 3.8cm and s2 = 6 cm as shown. At time t = 0, the loop enters a region of length L = 18.6 cm that contains a uniform magnetic field B = 1.2 T, directed in the positive z-direction. The loop continues through...
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A square loop of wire of side 2.8 cm and electrical resistance 79 ohms is near a long straight wire that carries a current of 6.9 A North. The long wire and loop both lie in the plane of the screen. THe left side of the loop is 9.0 cm from the wire. Find the motional emf if...
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A 1.2 kg rod that has a length of 1m and a resistance of 5 ohms slides with constant speed down a pair of frictionless vertical conducting rails that are joined at the bottom. Other than the rod, the rest of the circuit is resistance-less. A uniform magnetic field of...
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A generator consists of 250 turns of wire each with a radius of 8.7 cm. The armature turns with a frequency of 120 r/s in a magnetic field of 0.86 T
a.) What is the maximum emf generated? (4 marks)
b.) What is the average emf generated during the time interval while the...
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In the circuit (http://i.imgur.com/II38M.jpg),a variable resistor R is connected across the terminals of a battery, and an ideal ammeter and ideal voltmeter are also connected. In the figure, E is the internal emf of the battery, and r is its internal resistance. All the...
Hi all,
I have a certain problem I'm getting stuck on hopefully someone here can help
Homework Statement
A rectangular coil is 75 mm wide in the y-axis, 100mm long in the x-axis. What is the speed of the rotation if an rms voltage of 0,25 V is developed in the uniform field of B =...
Why the back emf of the primary coil always equal to the supply voltage but no greater than supply voltage(because of the large number of coil turns) when no loaded?Or it is a kind of dynamic equilibrium?If yes,how it reach equilibrium?
Thank you.
A Rectangular wire frame, is placed in a uniform magnetic field directed upward and normal to the screen. A side AB is connected to the spring . The spring is stretched and released when the part has come to a point A'B'(t=0). How would the induced emf vary with time? - Graph & Equation...
According to the faraday's law,the induced emf is proportional to the magnetic flux change linking the conductor.However,I wonder why there is induced emf when conductor is moving in uniform magnetic field,because i think that the magnetic flux linking to it is always the same as it move in...
Homework Statement
When a 60 \Omega resistor and a 120 \Omega are connected in parallel across a battery there is a current of 700 mA flowing through the battery. When the 120 Ohms resistor is disconnected from the circuit the current through the battery drops to 500 mA. What is the emf and the...
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I just took a test, and I am very unsure of the validity of how I approached the problem. Just looking for some feedback cause this is bugging me!
There is a circuit in the xz-plane (vertical), and the circuit has on it a gate. The gate is a pendulum of length L, which...
I had already posted this question in the homework category but since i did not get any replies i thought maybe i should post it here again...
A U shaped conducting tube is placed in a constant magnetic field in the downward direction. On the left of the tube is a resistance R.All other rods...
Homework Statement
A U shaped conducting tube is placed in a constant magnetic field in the downward direction. On the left of the tube is a resistance R.All other rods are assumed resistance less.On this tube a conducting rod is moving with constant velocity towards right with the help of an...
Dear Friends,
Well is EMF both conservative and non conservative at the same time, or is it simply a paradox.I have written a small article on it proving it's conservative and non conservative nature...
read it @: http://laps-of-mind.blogspot.com/2011/02/truth-about-emf.html"
well I need...
Faraday's law says that an induced voltage across a conductor is directly proportional to the rate of change of magnetic flux through the conductor, but I am having trouble getting my head round how it works in this situation.
Imagine a perfectly circular thin copper disc, and that this disc...
'it is emf when no current is flowing outside the cell. Whereas, it is potential difference is when current actually flows out of the cell."
"that emf is the potential difference when there is no current flowing through the circuit or when the key is open. Whereas, the circuit has certain...