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  • Describe methods to produce an electromotive force (emf) with a magnetic field or magnet and a loop of wire.

The apparatus used by Faraday to demonstrate that magnetic fields can create currents is illustrated in [link] . When the switch is closed, a magnetic field is produced in the coil on the top part of the iron ring and transmitted to the coil on the bottom part of the ring. The galvanometer is used to detect any current induced in the coil on the bottom. It was found that each time the switch is closed, the galvanometer detects a current in one direction in the coil on the bottom. Each time the switch is opened, the galvanometer detects a current in the opposite direction. Interestingly, if the switch remains closed or open for any length of time, there is no current through the galvanometer. Closing and opening the switch induces the current. It is the change in magnetic field that creates the current. More basic than the current that flows is the voltage that causes it. The current is a result of an voltage induced by a changing magnetic field , whether or not there is a path for current to flow.

The picture shows Faraday’s apparatus for demonstrating that a magnetic field can produce a current. It consists of a cylinder shaped battery. The positive end of the battery is connected to an open switch. There is a ring shaped iron core consisting of a set of coils one on the top and another at the bottom. The other end of the switch is connected to one end of the top coil. The other end of the top coil is connected back to the battery. Both the ends of the bottom coil are shown connected across a galvanometer box which shows a null deflection.
Faraday’s apparatus for demonstrating that a magnetic field can produce a current. A change in the field produced by the top coil induces an voltage and, hence, a current in the bottom coil. When the switch is opened and closed, the galvanometer registers currents in opposite directions. No current flows through the galvanometer when the switch remains closed or open.

An experiment easily performed and often done in physics labs is illustrated in [link] . A voltage is induced in the coil when a bar magnet is pushed in and out of it. Voltages of opposite signs are produced by motion in opposite directions, and the voltages are also reversed by reversing poles. The same results are produced if the coil is moved rather than the magnet—it is the relative motion that is important. The faster the motion, the greater the voltage, and there is no voltage when the magnet is stationary relative to the coil.

The diagram shows five stages of an experiment done by moving a magnet relative to a coil and measuring the e m f produced. The first stage of the experiment shows a wire coil with two loops connected across a galvanometer. The loop is in horizontal plane. A cylindrical rod shaped magnet is moved upward through the loop with the north pole of the magnet facing the loop and the South Pole away from the loop. The magnetic lines of force of the magnet are shown to emerge out from the North Pole and intersect the coil. A current is shown to be induced in the coil in clockwise direction. The galvanometer needle is shown to deflect toward right. The second stage of the experiment shows the next state of the first stage of the experiment. The cylindrical rod shaped magnet is now moved downward away from the loop with the north pole of the magnet facing the loop and South Pole away from the loop. The magnetic lines of force of the magnet are shown to emerge out from the North Pole and intersect the coil. A current is shown to be induced in the coil in anti clockwise direction. The galvanometer needle is shown to deflect toward left. The third stage of the experiment shows a wire coil with two loops connected across a galvanometer. The loop is in horizontal plane. A cylindrical rod shaped magnet is moved upward through the loop with the south pole of the magnet facing the loop and the North Pole away from the loop. The magnetic lines of force of the magnet are shown to merge into the South Pole and intersect the coil. A current is shown to be induced in the coil in anti clockwise direction. The galvanometer needle is shown to deflect toward left. The fourth stage of the experiment shows the next state of the third stage of the experiment. The cylindrical rod shaped magnet is now moved downward away from the loop with the south pole of the magnet facing the loop and the North Pole away from the loop. The magnetic lines of force of the magnet are shown to merge into the South Pole and intersect the coil. A current is shown to be induced in the coil in clockwise direction. The galvanometer needle is shown to deflect toward right. The fifth stage of the experiment shows a wire coil with two loops connected across a galvanometer. The loop is in horizontal plane. A cylindrical rod shaped magnet is held stationary near the loop with the north pole of the magnet facing the loop and south away from the loop. The magnetic lines of force of the magnet are shown to emerge out from the North Pole and intersect the coil. No current is induced in the coil. The galvanometer needle does not deflect.
Movement of a magnet relative to a coil produces voltage as shown. The same voltages are produced if the coil is moved relative to the magnet. The greater the speed, the greater the magnitude of the voltage, and the voltage is zero when there is no motion.

The method of inducing a voltage used in most electric generators is shown in [link] . A coil is rotated in a magnetic field, producing an alternating voltage (and current), which depends on rotation rate and other factors that will be explored in later sections. Note that the generator is remarkably similar in construction to a motor.

The figure shows a schematic diagram of an electric generator. It consists of a rotating rectangular coil placed between the two poles of a permanent magnet shown as two rectangular blocks curved on side facing the coil. The magnetic field B is shown pointing from the North to the South Pole. The two ends of this coil are connected to the two small rings. The two conducting carbon brushes are kept pressed separately on both the rings. The coil is attached to an axle with a handle at the other end. The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two brushes are connected to the galvanometer. A current is shown to flow in the coil in anti clockwise direction and the galvanometer shows a deflection.
Rotation of a coil in a magnetic field produces a voltage. This is the basic construction of a generator, where work done to turn the coil is converted to electric energy. Note the generator is very similar in construction to a motor.

So we see that changing the magnitude or direction of a magnetic field produces a voltage. Experiments revealed that there is a crucial quantity called the magnetic flux    , Φ size 12{Φ} {} , given by

Φ = B A ,

where B size 12{B} {} is the magnetic field strength over an area A size 12{A} {} , at an angle θ with the perpendicular to the area as shown in [link] . Any change in magnetic flux Φ size 12{Φ} {} induces a voltage. This process is defined to be electromagnetic induction    . Units of magnetic flux Φ size 12{Φ} {} are T m 2 size 12{T cdot m rSup { size 8{2} } } {} .

Figure shows a flat square shaped surface A. The magnetic field B is shown to act on the surface at an angle theta with the normal to the surface A. The cosine component of magnetic field B cos theta is shown to act parallel to the normal to the surface.
Magnetic flux Φ is related to the magnetic field and the area A over which it exists. Only the portion of the magnetic field that is perpendicular to the area ( B ) contributes to the flux. The flux Φ = B A is related to induction; any change in Φ induces a voltage.

All induction, including the examples given so far, arises from some change in magnetic flux Φ size 12{Φ} {} . For example, Faraday changed B size 12{B} {} and hence Φ size 12{Φ} {} when opening and closing the switch in his apparatus (shown in [link] ). This is also true for the bar magnet and coil shown in [link] . When rotating the coil of a generator, the angle θ size 12{θ} {} and, hence, Φ size 12{Φ} {} is changed. Just how great a voltage and what direction it takes depend on the change in Φ size 12{Φ} {} and how rapidly the change is made, as examined in the next section.

Section summary

  • The crucial quantity in induction is magnetic flux Φ , defined to be Φ = B A , where B is the magnetic field strength perpendicular to the area A .
  • Units of magnetic flux Φ size 12{Φ} {} are T m 2 size 12{T cdot m rSup { size 8{2} } } {} .
  • Any change in magnetic flux Φ size 12{Φ} {} induces a voltage—the process is defined to be electromagnetic induction.

Conceptual questions

How do the multiple-loop coils and iron ring in the version of Faraday’s apparatus shown in [link] enhance the observation of induced voltage?

When a magnet is thrust into a coil as in [link] (a), what is the direction of the force exerted by the coil on the magnet? Draw a diagram showing the direction of the current induced in the coil and the magnetic field it produces, to justify your response. How does the magnitude of the force depend on the resistance of the galvanometer?

Explain how magnetic flux can be zero when the magnetic field is not zero.

Is a voltage induced in the coil in [link] when it is stretched? If so, state why and give the direction of the induced current.

The first part of the figure shows a circular coil of wire held in a magnetic field. The magnetic field points into the paper. The coil is held using both the hands to stretch it. The second part of the figure shows the same circular coil of wire stretched in the magnetic field.
A circular coil of wire is stretched in a magnetic field.

Questions & Answers

mcq creativity involves
Sanjika Reply
send me the answers
Sanjika
mCQ creativity involves
Sanjika
ology means a study of
SharaAmor Reply
is a greek word means soul
SharaAmor
science
Tina
a branch of knowledge
Kanchan
psych means soul and ology means to study.
Wajid
Can someone help me with tha latent functions of different social institutions
Usman
***interestinglydifferenttopics.blogspot.com/2020/10/reflexes-psychological-debate.html Do check this out and please correct me if I'm wrong anywhere in this
Interestingly Reply
Factors that affect learning?
Ofentse Reply
I am struggling with survivors guilt and complicated grief after traumatic death of spouse. how to cope.
Rowdy Reply
Try to talk with someone you trust and join people who makes you feel worthy. try to help someone. Helping someone makes you feel better
sherlock
I think you must seek professional help.
Swarada
I am extremely sorry for your loss...I know that the pain of your loss is overwhelming and that you are experiencing all kinds of difficult and unexpected emotions. please don't get me wrong but the best way to cope is to move on..i know its hard..but that's the only way..(continued.)
Princess
stop burdening yourself with thoughts that say you could have done something..you couldn't..your just a human being and you cant always be a superman who saves the day..please dont feel guilty when you have no reason to..(cont.)
Princess
learn to love yourself again..learn to live ..for yourself,for the people who love you and need you in their lives.live for people who you once loved...Think about how you can make your life meaningful once again.It might seem impossible but trust me its necessary ..
Princess
Let your feelings of pain out ..you dont have to suffer ..talk to people whom you trust and love. take care and have a beautiful life ahead.
Princess
First and foremost -- Wow Rowdy! You have been through a highly difficult situation in your life, hands down. As a wife, I simply cannot phathom nor imagine slightly the feelings and thoughts you bare and I'm sure as these words do not help and hit rewind; my heart and prayers are going out to you-
Stephanie
today. I will say as well, everything you are feeling and going through, please know that these feelings and thoughts are all allowed, it is okay for you to find yourself feeling or thinking things that you would never find yourself wanting especially given the situation. I'm sure you question --
Stephanie
yourself, which in turn could make you question who you are right now and what this means for you as a person now and in the future. This is all okay, but there will have to be an understanding as to how to grow from these feelings and thoughts in a more humane manner l as these feelings and ---
Stephanie
thoughts could take a turn for a much more negative outcome as you find yourself trapped in a darkness that, if strong enough, trials and tribulations take years of complex development and experience, less strong minded individuals sometimes either never find the light, or end up being stuck in ----
Stephanie
a subconscious netherworld as they are consumed given the manipulation that was not understood to overcome. It results in losing all sense of heart, faith, soul and intelligence so that you don't grow, which in your case, growth is crucial. This is what your spouse will do their best in trying -----
Stephanie
to guide you through; keep an your senses wide open so that you can learn when she is trying to communicate.
Stephanie
What is meant by politics of intelligence? Please guide about this article.
Ali Reply
***scholar.google.com/scholar?q=politics+of+intelligence&hl=en&as_sdt=0&as_vis=1&oi=scholart#d=gs_qabs&u=%23p%3D_ckggUkdkPUJ
Angela
Thanks angela
Ali
Can u please explain it to me in your words?
Ali
Information about child psychology
Mohammed Reply
what is this
Maryam
any theory recommendations about socialization?
Geo
help me please:<
Geo
actually I don't know
Maryam
I badly need some for my research :<
Geo
But I need that😥
Mohammed
***courses.lumenlearning.com /boundless-sociology/chapter/theories-of-socialization/
Jobin
branches of psychology
QSN Reply
neuropsychology
jeddy
behaviorism
Mira
Legal psychology
Miljana
Developmental psychology, Sports psychology , Clinical psychology , Marketing psychology , counseling psychology , Biological psychology, Educational psychology , Positive psychology etc.
Swarada
child.psychology
Nss
social, occupational psychology
jeddy
what does it mean when the temporal lobe is anterior to occipital lobe
John Reply
the cortex refers to what part of the brain
John
the cortex refers to what part of the brain
John
cerebral cortex
jeddy
behind?
jeddy
in what time of situation is training most useful?
marjelee Reply
during bad experience
Nyakuei
i think its not about suitation, its about the thing tatz need training.
gokul
training is possibly warranted for all situations.
rhoda
I would think that training should be an ungoing thing. That's before, during and after. just in case there's a reoccurrence
Angela
any time
Aaronz
what is Karma
ana Reply
I think the summation of good and bad deeds you do in your life. Accidentally or otherwise.
Swarada
Yes. I totally agree.
ana
And if it is bad then the root must have been too.
ana
Yes , In Hinduism we also believe that our parent's Karma also applies to us ! Don't know about that , but it kept people in check .
Swarada
Adding to Swarada point. karma can be good or bad. both will have consequences. karma is biasedness you have shown in your life. like a king could not have two rules for normal man and his son, that comes under karma.
Sujeet
Oh perfectly said!
Swarada
Ok. It is also said that when one does something... bad or good..it will come back to you 10 folds of the same.
ana
yea that too ! I remember my mother always said if u stole someone's 10 rupees ur 100 will be stolen ( excuse my English ! I'm a non - English speaking person)
Swarada
karma is nothing but what one usually mean when they say- what you sow, so shall you reap.
Alisha
certainly
Crazy
more important.. this concept was told by lord Krishna as part of spirituality, to focus on your good deed ,the purpose you are born for and your responsibilities. Not for hoping that bad will happen with people who made you feel bad. just giving example ;)
Sujeet
karma is the boomerang of your actions. what u put out in the universe u get back
David
Who is the founder of psychology
Daryl Reply
Wilhelm wundt
Amanda
Wilhelm Wundt
Sneha
William wundth
Ihrar
Wilhelm Wundt
Megha
and William James
Amanda
Wilhelm Wundt
adam
Wilhelm Wundt is the founder of structuralism
Angela
Yes and also the "Father of Psychology" I think the correct word is Father not Founder.
Swarada
oh ok. noted
Angela
i believe it goes beyond him I believe it is Ancient but un formalized
David
I like your answer Swarada
David
Oh thanks! But u summarised it well!
Swarada
what is up my fellow psych peeps!!
what are some academic research on developmental psychology
Chezy
Sawrada Founder of Psychology is W.Wundt but Father of Psychology is Sigmund Freud...
Wajid
what are some good schools to study psychology?
Enjoy Reply
George Mason, Penn State, UVA, university of Michigan
Jasmine
Hi I'm currently doing my experimental psychology research can you suggest a topic or research topic for my research thank you and please see 😊
Jerico Reply
Hello Jerico. I could help you out with some ideas if you're interested!
Yasmine
can u give me some ideas too?
Geo
For sure. It depends if you're trying to do an experiment (using statistics probably) or a case study what are you aiming for?
Yasmine
Hello Jerico. Try to opt for something simple and easy to do. I wouls say perhaps study the effects of color on concentration? You could get a group of people and have them take a memory test (you can find some online) in a white room for example. Then have them take another memory test
Yasmine
similar to the first one but in a different room and then you check the responses if the performance is better
Yasmine
but you have to know that a lot of factors will interfere in the performance such as mental state etc so make sure to choose a certain specific population. that's very important
Yasmine
you could be a bit more specific about it , to isolate the variables that can mess it up like age, sex, etc... you gotta take that into account
Yasmine
so that the results get somewhat accurate
Yasmine
that is very detailed information I really like it thank you very much 😊 your so very kind
Jerico
You're very welcome
Yasmine
what are your interests in general?
Yasmine
Althogh I'm persuing botany and engineering.... but I also want to study human behaviour and psychology.... I would like if anyone can share their knowledge with me !!!!
Crazy
I'm interested on effect of electroconvulsive therapy on people having a depression
Jerico
What is Electroconvulsive therapy?
Pixeled
Astral Projection
Mansi
Electroconvulsive therapy (ECT) is a medical treatment that is most commonly used in patients with severe major depression.
Jerico
What are the expected dutties functions and responsibilities of a head of an agency based on the principles, Practice of industrial psychology?
Paul Reply
what are the psychological characteristics expected from an employee wether regular or occupying a position?
Paul
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Source:  OpenStax, Concepts of physics with linear momentum. OpenStax CNX. Aug 11, 2016 Download for free at http://legacy.cnx.org/content/col11960/1.9
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