Emf Definition and 901 Threads

Hello everyone :smile: I got a small question. In an electric motor when the coil rotates isn't this a change of magnetic flux. So wouldn't there be an induced emf in the coil? Any help would be appreciated. Thanks :smile:

Homework Statement A rectangular coil of 150 turns has dimensions of 23 x 70 cm and is located in a uniform 3 T magnetic field. In 1.2 s, the plane of the coil is rotated from a position where it makes an angle of 15° with the magnetic field to a position where it makes an angle of 72°...

Homework Statement http://img164.imageshack.us/img164/3313/qqqqo3.jpg Find the total magnetic flux through the coil at t=0 Given that the rate of change of flux at any time,t, is equal to 2 \pi f \phi sin 2 \pi ft, find the maximum instanteous value of the induced emf at any time & the...

Homework Statement An infinitely long conductor carrying a current I in the positive z-direction lies on the z-axis. A conducting triangle of wires lies in the yz-plane, which moves with a speed v in the positive y-direction. The following figure shows the situation on time t = 0: a)...

Homework Statement An coil has 4000 turns of wire and a mean area of cross-section 25cm^2. A magnetic field of flux density 0.16T passes through it. When the magnetic field is reduced steadily to zero in 0.0050s, emf is induced across the terminals of the coil. Calculate the value of this...

Homework Statement A torch battery has an emf of 6.0V and an internal resistance of 1 Ohms. What is the voltage measured by a voltmeter connected across the terminals of the battery, when the battery is connected to a bulb that draws 0.5 A from the battery? Anyways thanks I solved it.

Hi, I'm having some difficulties understanding some elementary physics concept. When different emf is supplied to a resistor of the same resistance, the p.d. across changes in different scenarios. By definition, p.d. is the amount of electrical energy converted to other forms of energy...

http://img.photobucket.com/albums/v345/crimsonflames/ddsa.jpg thats the circuit. isn't the equation emf = I(R+r) 0.032 * 900? isn't right and i know it isn't, so i don't know what to do! =(

Just thought i would ask, when a photodiode is acting in reverse bias, it allows current to pass but does not generate voltage. In fact, it has a voltage drop. When in forward bias, it allows current to pass but also generates an EMF. Is this correct, any response would be appreciated.

After following the thread "ideal conductor vs superconductor" a while, I am wondering about something that must have a simple answer. If you change the magnetic flux through a superconducting ring, what happens to induced emf?

Hello! I am a writer currently working on a children's science fiction novel. I need help with a problem of plot that hinges on my main character emitting an EMF field similar to an appliance like a hair dryer. This character is surrounded by this field and needs to get rid of it in a simple...

Hello, I am currently working through Faraday's Law and I am confused when my two textbooks don't explain how they set the polarity of V_{emf}, particularly when they say "the sign convention for V_{emf} is arbitrary in that it depends on the assumed direction for dS". How is the polarity...

A coil with 240 turns enclosing an area of 13.7 cm^2 is rotated in a time interval of 3.70×10^-2 s from a position where its plane is perpendicular to the Earth's magnetic field to one where its plane is parallel to the field. The Earth's magnetic field at the lab location is 5.9×10−5 T ...

Homework Statement A circular loop of wire is rotated at constant angular speed around an axis whose direction can be varied. In a region where a uniform magnetic field points straight down, what must be the orientation of the loop's axis of rotation if the induced emf is to be zero...

My background is in CS, so I apologize if I sound a bit stupid wrt the topic at hand. My friend and I have been having a heated debate about the causes of "discomfort" that I've been experiencing with my Macbook Pro. After having it on my lap for several minutes, even on top of surfaces that...

Say you had a circuit with a battery and a loop of wire somewhere in the middle of the circuit. The loop of wire is positioned so that it is free to rotate in a uniform magnetic field, and since a current is running through it, a torque will be supplied by the magnetic force allowing it to...

A circular loop of wire has a changing magnetic field running through it...however, the magnetic field is not touching the wire; its contained so that it simply runs through the loop without touching the wire. Apparently, there is still an emf through the wire even though the magnetic field is...

A circular loop of wire has a changing magnetic field running through it...however, the magnetic field is not touching the wire; its contained so that it simply runs through the loop without touching the wire. Apparently, there is still an emf through the wire even though the magnetic field is...

[SOLVED] Emf in a rectangular loop Homework Statement A rectangular loop (area = 0.15 m^2) turns in a uniform magnetic field, B = 0.16 T. When the angle between the field and the normal to the plane of the loop is pi/2 rad and increasing at 0.70 rad/s, what emf is induced in the loop...

1)When the current through the coil of a motor flows it cases the coil to spin. 2)The spinning motion causes the wires in the coil to cut through the magnetic field. 3)The current induced (back EMF) in the wires by this spinning motion opposes the change that causes it. (Lenz's Law)...

[SOLVED] EMF problem - Current in Coil Homework Statement A small square coil is located inside an ideal solenoid at the center with its plane oriented perpendicular to the axis of the solenoid. The resistance of this coil is 2.00 \Omega and each side is 4.00 cm long. The solenoid has 125...

Ok, this may borderline a homework problem, but I'm not quite grasping the concept of induced electric fields. So let's say that they exist a wire loop and solenoid. The switch in the circuit containing the solenoid is originally open and then closed. At this instant, we induce an emf in the...

Homework Statement An automobile starter motor draws a current of 1.9 A from a 5.5 V battery when operating at normal speed. A broken pulley locks the armature in position, and the current increases to 8.6 A. What was the back emf of the motor when operating normally? Answer in units of...

Homework Statement A wire is bent into three circular segments each of radius r=9.2 cm. each segment is a quadrant of circle, ab lying in the xy plane, bc, in the yz plane, and ca lying in the zx plane. If a uniform magnetic field points in the positive x direction, what is in volts the...

A metal disc is placed in a uniform magnetic field of flux density,B,acting through the plane of the disc at and angle,\theta.When the dis is rotated an e.m.f. is induced between the centre and the rim of the disc. http://img158.imageshack.us/my.php?image=scanlc2.jpg Design an experiment...

Homework Statement a) If B (magnetic field) is perpendicular to the plane of a circular loop, then is it true that when B increases the induced emf is clockwise and when the B decreases the emf is counterclockwise? Or do you need to know whether it is pointing into/out of the page? Or would...

Homework Statement The voltmeter is removed (previous question was a voltmeter connected to a battery and it reads 12 V) and a resistor of 21 ohm is connected to the battery. What is the current (I) through the battery? Homework Equations emf=V I=emf/(R+r) The Attempt at a...

Homework Statement A magnetic field is perpendicular to the plane of a single-turn circular coil. The magnitude of the field is changing, so that an emf of 0.91 V and a current of 3.2 A are induced in the coil. The wire is the re-formed into a single-turn square coil, which is used in the...

Homework Statement A magnetic field is perpendicular to the plane of a single-turn circular coil. The magnitude of the field is changing, so that an emf of 0.76 V and a current of 3.1 A are induced in the coil. The wire is the re-formed into a single-turn square coil, which is used in the same...

Homework Statement A radio antenna that receives an AM radio station that emits at 800 kHz is constituted of an inductor of 120 turns with a radius of 0.6cm. The inductor is home to an iduced emf du to a magnetic field oscillating from the radio wave. The magnetic field is...

Homework Statement What is the resistance R? (R1=15.13 Ω, I1=2.77 mA , I2=1.81 mA. Give answer in Ω.) What is the emf of the battery? Homework Equations I = E/R The Attempt at a Solution How do I solve this with the batteries EMF?

[SOLVED] Induced emf: Faraday's Law and Lenz's Law Question The plane of a conductive loop with an area of 0.020 m^2 is perpendicular to a uniform magnetic field of 0.30 T. If the field drops to zero in 0.0045 s, what is the magnitude of the average emf induced in the loop...

Could someone perhaps explain how a potentiometer can be used to measure an unknown emf? My book gives a bad explanation...

Hi! I read this article about Faraday's law, which states, that the emf will be always negative, by the formula, is this http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html"

Homework Statement Hi all, In school, I tried to investigate how the emf (voltage) of a fruit cell varies with temperature. I took ~200ml of freshly squeezed orange juice, 2 copper electrodes, a voltmeter, heater and thermometer. I set up everything, and got an initial voltage of somewhere...

Homework Statement The solenoid has N turns of wire around a cylinder. The radius of the cylinder is "a" and length is "b." THe current of the solenoid varies as I(t)= I_{0}(1 - e^-\alphat) . I_{0} and \alpha are positive constants. Around the solenoid is a square loop of wire with side...

I hope someone can help me with my coursework by making sure my method is ok and is actually correct for my experiment. Note. I will not actually be doing this it is just a plan of what I could do! 1. I am provided with a cell of approcimate EMF 1.5V, an approximate internal resistance of 1Ω...

Homework Statement A circular loop of wire can be used as a radio antenna. If an antenna with a diameter of 20.0 cm is located a distance of 2.40 km away from a from a source with a total power of 45.0 kW at a frequency of 101 MHz, what is the maximum emf induced in the loop? (Assume that the...

Homework Statement If the current is increasing at a rate of 0.1 A/sec what would the induced emf in a loop of 0.5 m be? Homework Equations I = \frac{|emf|}{R} emf = - \frac{d}{dt} B A cos(\theta) I'm obviously missing an equation or something. Some guidance would be much...

Homework Statement In a ring of radius R, there is current I flowing in the counterclockwise direction as viewed from above. A small ring of radius r is on a common axis and is a hight z above the current carrying ring, where z>>R. The small ring moves up with velocity v. Calculate the emf in...

Homework Statement Hi, my first post here. :smile: Anyway I am struggling with this homework, can someone help me out, show me what to do please. 1)a cell can supply a current of 1.2A through two 2ohm resistors connected in parallel. When they are connected in series the value of the...

Your opinion to the following will be appreciated Lets imagine a sphere made of a conductor (copper) placed within a static magnetic field. The field will penetrate the within the shier. Next we place inside the sphere a coil producing a variable electromagnetic field. The electromagnetic field...

Homework Statement You'll have to forgive me... I've got some rather poor Physics books with which to consult, so this may seem rather simple. I think I understand the concepts but I don't think I have all of the information from my sources to answer this problem. A 1.5 V battery stores...

Hi guys - Here's the problem I'm stuck on: In a physics laboratory experiment, a coil with 160 turns enclosing an area of 13.7 (cm^2) is rotated during the time interval 4.60×10−2(s) from a position in which its plane is perpendicular to Earth's magnetic field to one in which its plane...

On a particular dynamo, the rotating coil has 500 loops, each of area 2.5x10-4 m2. The magnetic field can assumed to uniform and of magnitude 0.400T. When the bicycle is ridden at a particular speed, the coil rotates with a frequency of 8Hz. What is the maximum emf produced? What is the average...

just a simple question, why is it that in almost all circuits where a battery is the source of DC , the EMF is considered to be constant over time while in reality is it not ? The EMF is a decreasing function w.r.t time considering the battery is operating.

well iwas going through the standard example that is there is a uniform magnetic field in aregion going into the palne and ther is a rectangular 'loop' with one side which can slide on metallic rods with constant speed v and the the relation \epsilon=BLv well the example is (almost) here well...

Homework Statement Given: u_0 = 1.25664e-6 A 2 m long large coil with a radius of 14.6 cm and 320 turns surrounds a 4.2 m long solenoid with a radius of 4.6 cm and 7700 turns. The current in the solenoid changes as I = I_0 sin (2pi*f*t) where I_0= 30 A and f=60 Hz.Inside solenoid has...

Homework Statement "A square loop of wire is held in a uniform magnetic field of .24 T directed perpendicular to the plane of the loop. The length of each side of the square is decreasing at a constant ratee of 5.0 cm/s. What is the emf induced in the loop when the length 12 cm...

im thinking of the classic airplane problem. the one where the flying airplane develops a voltage across its wingspan. now this was posed to me as a motional emf problem and i bought it then but simultaneously thought that it seemed like a hall effect problem. so two questions now that i think...