Rev. Notes > IGCSE > Electromagnetic Effects Previous Topic Electromagnetic Effects Next Topic Topics
 Induced e.m.f. Factors affecting the magnitude of induced e.m.f. Lenz's law A.C. Generator Rotating-coil generator and use of slip rings Graph - output voltage against time for an A.C. Generator Transformer Advantages of high voltage transmission Energy losses in transformer Magnetic field due to a current in a straight wire Magnetic field arroud a current carrying solenoid Force on a current carrying conductor inside the magnetic field D.C Motor Difference between slip rings and split rings Test Yourself

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## Transformer

It consists of two coils, primary and the secondary, linked by a soft iron core.

 Remember, primary and secondary coils are made up of copper (Cu) material, while core is made up of iron material.

When magnetic field is changed across the primary coil by connecting it with A.C. (Alternating Current), an e.m.f. induces across the secondary coil. The iron core channels the alternating field through the secondary coil, inducing an alternating e.m.f. across it.

The output voltage from the transformer depends on the input voltage and the number of turns in priomary and secondary coiils.

If there are more turns in the secondary coil as compared to the primary coil, output will be higher than input and the transformer works as step-up transformer.

If there are less number of turns in the secondary coil as compared to the primary coil, then output will be less than input and the transformer works as step-down transformer.

There are two important equations of the tranformer which are as under.

First equation:

Vp/Vs = Np / Ns

Where

Vp = Voltage across the primary coil

Vs = Voltage across the secondary coil

Np = Number of turns in the primary coil

Ns = Number of turns in the secondary coil

Second equation:

Vp / Vs = Is / I(By using this equation, We asssume that transformer is 100% efficient, means Input Power = Output Power OR VpIp= VsIs)

Where

Vp = Voltage across the primary coil

Vs = Voltage across the secondary coil

Ip = Electric current flowing through the primary coil

Is = Electric current flowing through the secondary coil

 Munawar Ahmed Said : Dear Sir, A brilliant try for motivating IGCSE student but please try to convey in colourful manner 14/10/16 09:17 PM

 Allan Said : The answer looks a little lite on information. I take it there's proably room for more info on the slip ring difference, and how this impacts the electromagnetic field, no? Any thoughts of expanding it? Resources like this might be a good source of info: http://powerbyproxi.com/slip-ring/ . That, or a quick google search ;/ Just a thought! Otherwise, the comments section has been super helpful. Thanks 30/09/16 03:23 AM

 DIVYANSHU SAINI Said : AND WHAT ABOUT THE POWER LOSES 02/05/16 09:13 AM

 DIVYANSHU SAINI Said : WHICH WILL INDUCE MORE E.M.F (A) IF A CYLINDRICAL MAGNET IS ROTATED INSIDE A COIL (B) IF COIL IS ROTATED IN AN MAGNETIC FIELD OF SAME STRENGTH (C) IF THE CYLINDRICAL MAGNET IN (A) IS REPLACED BY SOME OTHER TYPE OF MAGNET (ie. BY A BAR MAGNET OR A MAGNET IN FORM OF A CYLINDER BUT HAVING GAPS AS IN AN ELECTRIC MOTOR) PLEASE NOTIFY ME ON DIVYANSHUMRWAL@GMAIL.COM IF YOU CAN. AND PLEASE REPLY WITH REASONS THAT WHY WHY THIS OPTION AND WHY NOT. AND ONE THING MORE "INSTENTLY" 02/05/16 09:05 AM

 Mohammed Ilyas Said : Haris you should mention that the thumb has to be in the direction of the current in the wire 06/10/15 08:34 PM

 z Said : not much information needs improvement 06/10/15 08:22 PM

 Mohammed Ilyas Said : Isn't the equation Vp x Ip = Vs x Is? that's how i found it in some other sources 06/10/15 08:16 PM

 haris Haseeb Said : How to apply right hand grip rule ? Hold a wire in your hand. The thumb shows the way of current flow and the fingers shows us the magnetic field is it right sir ...? 06/10/15 07:59 PM

 hudeyfa ali Said : thanks 06/10/15 07:28 PM

 abdulrahman murad Said : An electric current passes through a solenoid, resulting in a magnetic field. When wrapping the right hand around the solenoid with the fingers in the direction of the conventional current, the thumb points in the direction of the magnetic north pole.------------------------------------------------------------------------------------- Admin Replied:  Great! 06/10/15 06:57 PM

 hudeyfa ali Said : what is right hand grip rule and how to apply it ? 06/10/15 06:39 PM

 unknown Said : what is kick? 03/10/15 08:19 PM

 feras maen Said : what do you assume,when you apply the transformer equation VpIp=VsIs Ans. We assume that the transformer is 100% efficient. 03/10/15 04:52 PM

 hudeyfa ali Said : thanks 03/10/15 01:38 PM

 Mohammed Adel Said : I haven't understood it yet ------------------------------------------------------------------------------------- Admin Replied: Thank you very much for your remarks. In which topic you are facing difficulty to understand? Can you please mention that? We are always here to assist you. 28/09/15 04:57 PM

 Saiba Muhammed Said : I can not see the picture could you please upload it soon...? ------------------------------------------------------------------------------------- Admin Replied: If you are asking for an article of "induced e.m.f.", then it is already uploaded. Thanks 19/05/15 04:08 PM

 Anon Said : Its Vp/Vs=Is/Ip 27/04/15 03:28 PM

 Anonymous Said : Its meant to be Vp/Vs=Ip/Is Not Vp/Vs=Ip=Is 22/03/15 09:27 PM

 Anonymous Said : Its meant to be Vp/Vs=Ip/Is Not Vp/Vs=Ip=Is 22/03/15 09:27 PM

 okolie victor (imsu) Said : ok but pls more details 17/10/14 06:10 PM

 victor okolie Said : please can I see the diagram 17/10/14 06:06 PM

 tammy gibson Said : i think you should add the effects of on the output voltage if the coil is made to turn faster 11/08/14 05:34 PM

 Anonymous Said : The site is very good but please check your grammar i.e you made many typing errors. 06/07/14 11:52 AM

 Professor joe Said : I think that some more effort is to be put in it. Thereafter I want to say that igcse is easy. Just log on to some appropriate sites and videos. Kapish. Yo 13/04/14 04:37 PM

 lppen Said : they were no notes 26/03/14 08:16 PM

 Nisar Said : Everyone says that P=I^2.R, And by having high voltage we have low current, so low energy losses but another formula, P=V^2/R, According to this if voltage will be increased Power Loss will also be increased.....How we will justify this????????/ 06/03/14 05:46 PM

 dinesh Said : thanks 15/02/14 07:45 PM

 Kunal Mshra Said : This Diagram Really Explains alot. 10/12/13 07:42 PM

 electricslipringcom Said : JINPAT Electronics is a leading manufacturer in industrial slip rings. We commit ourselves to the development, designing and manufacturing of different types of high quality slip rings for a vast variety of applications. We provide standard products as well as customized products according to your needs. We have also collaborated with Consortium of Industry including Military Industry and Universities in China. http://www.electricslipring.com/ 26/09/13 11:12 AM

 dalha nigeria Said : why not list the factors above and later explain them for easy identification 20/08/13 12:54 AM

 alvin xavier Said : derivations shud b provided 04/03/13 05:24 PM

 claire Said : Where are the diagrams????? 13/01/13 09:29 AM

 Adan Said : Very useful but will be great if diagrams were added to explain more. 21/11/12 12:11 PM

 Nabila Said : The notes are very helpful but there are no pictures or diagrams to make the student understand more. These might be small things but there are very helpful for a student. 20/09/12 08:49 PM

 kishor Said : its usefull 29/07/12 04:28 PM

 sarah Said : you spelled generator wrong its not gennerator :)------------------------------------------------------------------------------------- Admin Replied: Thanks for pointing that out sarah, we will edit the notes soon so that they are more accurate. Keep visiting 30/04/12 06:01 PM

 Gia Said : can u please add some pictures on AC generators and DC motors? thank you!------------------------------------------------------------------------------------- Admin Replied: Thank you, We will try our best to post more illustrations of AC generators & DC motors. Just stay tuned. 27/04/12 07:01 PM

 harshil Said : its to short and not explained properly with image------------------------------------------------------------------------------------- Admin Replied: Thank you for your comment, we will make sure we provide further explaination asap. 03/04/12 03:05 PM

 kazakh Said : there is no image 18/02/12 06:09 PM