Investigation on Transformers.

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Rahul Bose

Investigation on Transformers

Background Information on Transformers

“Every transformer has three parts: (Physics, David Sang Chapter 21 pg 342)

  • Primary Coil – incoming voltage V1 is connected across the coil
  • Secondary Coil – this provides the voltage V2 to the external circuit
  • Iron core- this links the two coils”

The turns ratio tells us the factor by which the voltage changes:

  • A step-up transformers increases the voltage – there are more turns on the secondary than on the primary
  • A step-down transformer reduces the voltage – there are fewer turns on the secondary than on the primary.

There is a “transformer equation”, relating Vp and Vs to the number of turns on each coil, Np and Ns can be derived. The equation is Vp/Vs = Np/Ns.  This tells us that since the magnetic field in each coil is the same, it follows that the e.m.f in each coil is proportional to the number of turns in the coil. (Physics, David Sang Chapter 21 pg 342)  

 How do they work?

“Transformers only work with alternating current (a.c.). The alternating current in the primary coil produces a varying magnetic field in the core. The core transports this alternating field around to the secondary coil. This induces a varying current in the secondary coil.” (Physics, David Sang Chapter 21 pg 342)  

Variables

  • Input Voltage- This is the only variable being changed in this experiment. The voltage will be altered throughout the experiment
  • Number of turns on the primary coil- This variable will be kept constant.  In my experiment the number of turns are 50.
  • Number of turns on the secondary coil- This variable will be kept constant. In my experiment the number of the turns will be 100. Therefore the ‘turn ratio’ will be 1:2.
  • The material used for the core- This variable will be kept constant. In my experiment the core is made out of Iron.
  • Separation of the wire- This variable will be kept constant as well. The secondary coil will be turned on top of the primary coil.

Equipment required for the experiment

  • 2x Voltmeter
  • Iron Rod
  • Crocodile Clips
  • Power pack
  • Coil
  • Insulation Tape
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Method

In this experiment I intend to investigate how altering the input voltage affects the output voltage.  To do this I will use a power pack with an alternating current.  I will wire it up to two digital voltmeters. The first voltmeter will be attached to the primary coil. The second voltmeter will be attached to the secondary coil. Both voltmeters will be connected in parallel. The primary coil, with 50 turns, will be wound around an iron core (rod) and the secondary coil, with 100 turns will be wound over the primary coil.  The transformer that I will make ...

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