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.
Homework Statement
S is a disk of Area 0.003m2, B is a magnetic field perpendicular to S and increasing at 0.02 T per second. What is the EMF in the perimeter of S?
Homework Equations
I assume we need a formula relating Area, B and emf - Faraday's law of induction? or possibly phi =...
If there is electromagnetic induction on an object that has no resistance, will an emf be produced? I know that no current would flow but is emf produced?
Thanks.
Ok, now I got another question while doing electromagnetic induction questions.
I know flux linkage=NBA and in a rotating coil, Flux linkage=NBA cos wt, which differentiated (Faraday's Law) wrt time gives E=NBAw sin wt, where w = angular frequency.
However, when the plane of the coil is...
My doubt is that when we charge a battery we say that energy is transferred into it , but does the emf of a battery change in this process ? Is the emf same before and after charging , if yes then what actually happens during charging a battery ??
pls help !
1. A 50 g horizontal metal bar, 12 cm long, is free to slide up and down between two tall, vertical metal rods. A 0.060 T magnetic field is directed perpendicular to the plane of the rods. The bar is raised to near the top of the rods, and a 1.0 Ohm resistor is connected across the two rods at...
Homework Statement
1. A 109.3 mH inductor whose windings have a resistance of 3.6 Ω is connected across a 11 V battery having an internal resistance of 1.83 Ω. How much energy is stored in the inductor?
2. The maximum allowable potential difference across a 225.7 mH inductor is 401...
Homework Statement
a tightly wound circular coil has 36.8 turns, each of radius .1m. the uniform magnetic field is in a direction perpendicular to the plane of the coil. the field increased linearly from 0 to .42t in a time of .251s.
what is the emf induced in the windings of the coil...
(Solved.) 2 Unknown Currents, 1 Unknown emf, and a little confusion to boot!
First off, hello everyone! I just formally joined the forums today after reading discussions from the shadows for a while now.
This summer I'm taking the second part of a 200 level physics course and the...
Homework Statement
A solid conductor travels at 150 m/s across a uniform .045T magnetic field. Which side is positively charged and what is the emf across this block?
Homework Equations
I actually solved for the emf no problem. I am having difficulty determining which side is...
1. Is there an electric motor of any type that does not produce back emf.
2. Is it possible to design a motor that does not generate back emf.
3.What are the demerits of designing a motor that do not produce back emf.
4. What are the merits of having a motor that generate back emf.
5...
What causes the back emf in motors (brushless DC motors to be exact).
First thing is the rotating magnetic field of the rotor, which cuts the stator coils inducing an emf in the opposite direction. This would increase as speed increases. This is just a generator.
Second, what about self...
Graph to show the variation of the p.d. V across the battery with current I as R is varied.
i) Draw line of best fit.
ii) Use it to determine the emf of the battery;
and the internal resistance r of the battery.
The gradient \approx \frac{\Delta V}{\Delta I} = 1.67 \Omega...
Homework Statement
A plane EM wave in Vaccum is given by E = y Eo ei (kz-wt) with Eo = 1 V/m( real valued)
and wavelength λ= 10 m. A circular loop of radius a =1 m is located with its center at origin but Oriented so that a diameter lies along the z-axis while the plane of the loop...
heres the question:
A 110 turn coil has a radius of 4.1 cm and a resistance of 25 Ohm. The coil is in a uniform magnetic field that is perpendicular to the plane of the coil. What rate of change of the magnetic field strength will induce a current of 4.3 A in the coil? What rate of change of...
Homework Statement
A 5.60ohm resistor is connected to a battery that has 0.200ohm internal resistance, and a terminal voltage of the battery is 10.0V. What is the current in the resistor? What is the emf of the battery?
Homework Equations
EMF=terminal voltage+(I)(Rint.)
V=RI
The...
Homework Statement
A battery supplies a steady current of 5.6 A for 21s. During this time 1410J of chemical energy is transformed into electric energy, but 560J of this electric energy is transformed into heat energy inside the battery.
a) What is the emf of the battery?
b) What is the...
Homework Statement
Im currently in my last year of high school, and I'm writing a report on AC generators. I've heard a number of different things from different sources. When the coil is perpendicular to the magnetic field, maximum magnetic flux is flowing through the coil. This is then at a...
A small loop of area A is placed inside a long solenoid that has n turns per meter and carries a sinusoidally varying current of amplitude i. The central axes of the loop and solenoid coincide. If i = i0sin ωt, find the emf in the loop.
EMFinduced = - d(\phiB)/ dt
\phiB=BA
Bsolenoid=...
Homework Statement
a straight horizontal rod slides along parallel conducting rails at an angle with the horizontal of 30 degrees (inclined plane). The rails are connected at the bottom by a horizontal rail so that the rod and rails form a closed rectangular loop. A uniform vertical field...
Homework Statement
Hi I need some concepts on magnetic fields explained to me. 1.)
I know in theory that if you have a current carrying conductor say along the X-axis then the magnetic field generated would be in the y,z components
So let's say I wish to measure the magnetic field in real...
the emf is defined as the potential difference between two points \varphi(\vec{r_1})-\varphi(\vec{r_2}).
ok so let's say we make a trip round a closed circular wire with a battery to keep the current flowing then r1=r2 and so no emf has been done - is this true and if so why?
Faraday's law says
induced emf = - d(flux)/dt
If this is applied to a loop where induced emf causes currents, and thus flux itself, do we have to consider that flux (of course we don't if it's constant)?
If the external flux has a nonzero second derivative, then the induced emf is...
Homework Statement
A real battery is not just an emf. We can model a real 1.5 battery as a 1.5 emf in series with a resistor known as the "internal resistance", as shown in the figure (Intro 1 figure) . A typical battery has 1.0 Ohm internal resistance due to imperfections that limit...
Homework Statement
1. When a 100 loop coil of wire of radius 2.00 cm is rotated in a uniform magnetic field,B=0.500T , so that it goes from maximum flux to zero flux in 0.0320 s, find the average emf induced between the terminals of the coil.Homework Equations
Max Flux=BAcos(0)=Change in...
Two straight conducting rails form a right angle where their ends are joined. A conducting bar in contact with the rails starts at the vertex at time t = 0 and moves with a constant velocity of 7.00 m/s along them, as shown in Fig 31-44. A magnetic field with B = 0.350 T is directed out of the...
Hi,
I have a problem about EMF and/or Voltage.
Let their are 100 electron at a place A and 200 electron at place B. Now what will be the Voltage/EMF (Voltage or EMF difference)?
And How to calculate it ??
In other words "How can I calculate Voltage or EMF if I know only Charge...
Homework Statement
The component of the external magnetic field along the central axis of a 50 turn coil of radius 4.7 cm decreases from 1.8 T to 0 T in 4.3 s.
If the resistance of the coil is 2.8 , what is the magnitude of the induced current in the coil?
Homework Equations...
Homework Statement
A 11.2m long steel been is dropped from a height of 9.51m. The horizontal component of the Earth's over the region is 18.5x10^-6T. What's the emf in the beam impact just before the impact with the earth, assuming its long dimension remains in a horizontal plane, oriented...
If a cell is connected with an external resistor of 6V and a switch and a voltmeter is connected across the terminals of the cell which reads 2.6 V when the switch is open and 2.4 V when the switch is closed, how do you find the emf and the internal resistance?
so far i tried doing:
V = IR...
Homework Statement
When a wire carries an AC current with a known frequency you can use a Rogowski
coil to determine the amplitude Imax of the current without disconnecting the wire to
shunt the current in a meter. The Rogowski coil, shown in the figure, simply clips
around the wire. It...
Homework Statement
Suppose you wrap wire onto the core from a roll Nof cellophane tape to make a coil.
Describe how you can use a bar magnet to produce an induced voltage in the coil.
What is the order of magnitude of the emf you generate? State the quantities you
take as data and their...
A motor with a brush-and-commutator arrangement has a circular coil with radius 2.5 cm and 150 turns of wire. The magnetic field has magnitude 0.06 T and the coil rotates at 440 rev/min.What is the average back emf?
i have tried this
Flux=Magnetix Field*Area
Flux=0.06*pi*r^2
Here...
Homework Statement
A 800-turn solenoid, 18 cm long, has a diameter of 2.9 cm. A 15-turn coil is wound tightly around the center of the solenoid.
If the current in the solenoid increases uniformly from 0 to 3.1 A in 0.28 s, what will be the induced emf in the short coil during this time...
Hi,
I'm trying to figure out how you can calculate motional EMF when the velocity of the object in question is not perpendicular to the magnetic field. There are two equations in my textbook, but the text describing them is not very helpful.
The first is \varepsilon = vBL, which can be...
Homework Statement
Resistance = R
Radius = r
Angle = theta
B = 2cos(2t)
Circular wire loop where magnetic field acts at theta degrees with respect to the normal of the wire loop.
Find induced current and emf in wire loop. Find induced electric field at radial distance d from center of wire...
I need some help in appreciating this consensus.
We are told the following things:
- that we have anti-electrons, anti-protons but no anti-photons.
- that photons - or more specifically emr - have an electrical component and a magnetic component.
- the the magnetic component of emr runs 90...
So here is the circuit I came up with to represent back emf in a DC motor with rotational inertia.
When current is applied to the motor it spins. When it rotates, the motor acts as a generator and creates a voltage (back emf) as shown (sorry for the incorrect notation, I don't know the...
(As magnitudes)
Faraday's law states that induced emf in a conducting loop by a changing flux, say x, is:
emf = dx/dt
Now if we have a circuit with the loop in series with wires (which are then tied together), how do I picture the voltages/currents in this circuit?
I mean, the actual...
Homework Statement
Our teacher just posted this question online. We have less than an hour to figure it out. Can someone help point me in the right direction.
Your team has devised an orbiting “drop cable”
system that creates an induced EMF by moving a cable through a
magnetic field...
See question below:
http://img140.imageshack.us/img140/479/30680788kr3.th.jpg
In order to calculate the EMF, the markscheme using the formula "E=Blv", the markscheme uses the linear speed of point M. Can someone please explain why this is the case - I understand the derivation of E=Blv, just...
I realize this is probably a very simple question, but for some reason I'm getting very confused.
Homework Statement
A motor is connected to a 12 V dc supply and draws 5.0 A when it first starts. What will be the back emf when the motor is operating at full speed and drawing 1.2 A...
A coil is located at the center of a long solenoid of radius R = 15cm which has 5x10^7 turns per meter and carries a current I = 16A. The coil is coaxial with the solenoid and consists of 5 turns of wire each in the shape of a square of length a = 5cm on each side.What is the magnetic flux...
Homework Statement
This question is my translation but there should be all info needed.
First part:
Calculate the emf and standard electrode potential of the cell Zn/ZnO/KOH(aq)/Ag2O/Ag
ZnO(s)+H2O(l)+2e- =>Zn(s)+2OH-(aq) E=-1,26V
Ag2O(s)+H2O(l)+2e- =>2Ag(s)+OH-(aq) E=0,342V...
The rectangular loop in the figure has 1.7×10^−2 ohm resistance. What is the induced at this instant? See picture below. Answer is in terms of I, like 5*I.
emf = Bvl
I= emf/R
B= [\mu_0 / 2*pi] *I * ln(.03/.02) since the magnetic field goes through the loop from 2cm to 3cm
then I used...
The question was to find I1 I2 and E. I got those parts of the question correct.
I1= 1 A
I2 = 2A
E = 15V.
But the only reason I got these right is because the arrows for I1 & I2 were given in the attached figure. The directions of the current don't make sense to me. If the EMF from...