Induction coil (or Rhumkorff coil) - construction and working


Induction coil (or Rhumkorff coil) 

Induction coil (or Rhumkorff coil) is one among the electrical devices that has wide number of applications. This concept  covers a major place in physics, especially in the field of magnetism . It is because of its importance that has inspired me to write something about it.

That's why in today's article I would like to share with you an interesting topic related to Induction coil (or Rhumkorff coil) . I hope after reading this article, your confusions would be clear and help you a lot.

Induction coil (or Rhumkorff coil)
Induction coil (or Rhumkorff coil)

What is an Induction Coil ?

Induction Coil is a device used to produce high potential difference using a source of low potential difference (say a battery of 2 to 6 volt).


Induction Coil is based on the principle of mutual induction. 


It consists of the following components :

1) Primary coil: 

Primary coil consists of few thick insulated copper wire wounded on a core made of a bundle of soft iron wires,  insulated from each other to minimize losses due to eddy currents.

2) Secondary coil :

secondary coil consists of number of turns of thin insulated copper wire. It is wounded over the primary coil and it's ends are connected to a spark gap across which high potential difference is obtained. The resistance of secondary coil is very high. 

3) Automatic make and break arrangement:

It consists of an iron hammer H mounted against the iron core, and a platinum contact point P1 , which makes contact with another similar contact point  P2.

4) Capacitor :

A parallel plate capacitor of about 1 micro farad capacitance is connected across the automatic make and break arrangement. 

5) Battery :

one end of the primary coil is connected with one terminal of the battery and the other end of the primary coil is connected to the second terminal of the battery through the make and break arrangement. 

Working and Theory of Induction coil (or Rhumkorff coil):

The contact points P and  P2 are initially in contact with each other as shown in the figure 2. On pressing the key K,  current flows in the primary coil P and hence the iron core gets magnetised .

Induction coil (or Rhumkorff coil), working and theory of Induction coil (or Rhumkorff coil)
Working and theory of Induction coil (or Rhumkorff coil)

 The magnetised iron core attracts the iron hammer H. As the hammer moves towards the core ,the contact breaks between the coils P1 and  P2 . The current in the primary coil decays, as soon as the contact is broken and the iron core is demagnetised. The hammer denoted as H is pulled back and again there is contact between coils P1 and  P2 . This closes the circuit again and the process is repeated.

At the time of make,  the magnetic flux linked with the secondary coil produces induced EMF across the ends of the secondary coil. At the time of a break,  the magnetic flux linked with the secondary coil induces the EMF across it's ends in the opposite direction.

The self inductance of the primary coil opposes the rate of growth and decay of current through it. 

The decay of current in the inductor or primary coil is given by :

                   I = I₀e(-R/L) t     or dI/dt = (-R/L ) I₀e(-R/L) t  = (-R/L)  I

R denotes the resistance and L is the self induction of the primary coil. 

In the secondary coil, the magnitude of induced EMF is proportional to the rate of change of current with respect to time. so, before producing large EMF across the ends of a secondary coil, the value of R should be very high and the value of L which denotes the inductance should be very low at the time of make and break.

The resistance of primary circuit is very large at break than at make, so the time constant denoted as L/R is very small at the break than at the make.

Thus we can say that the magnetic flux dies off more quickly at the break than it is established at the make. Hence the induced EMF set up across the secondary coil at the break is much more than at the make. 

At the same time, due to the phenomenon of self induction, induced EMF is set up in the primary coil . This induced EMF is concentrated at the contact points P1 and  P2.

During the break , when the points P1 and P2 are apart,  They offer high resistance to the flow of induced current and hence sparking between them may take place but the capacitor connected across them absorbs the energy of the charges at the end of the contact points and hence avoids the sparking between the points. The sparking may otherwise lead to the melting of contact points.

The capacitor serves the following three purposes :

1) The spark appearing across the platinum tips is quenched by the capacitor. 

2) At the "make " mode of contacts, the capacitor decreases the EMF in the secondary coil. 

3) At the "break" mode of contacts, it increases the EMF in the secondary coil.

Through the primary coil, the capacitor gets discharged and in turn supplies the current to the primary coil in the direction opposite to the direction of the current supplied to it by the battery. The reverse current in the primary coil supplied by the discharge of capacitor enables the complete and rapid collapsing of the magnetic flux at the break. Thus the efficiency of the Induction Coil for producing a very high EMF is increased with the presence of the capacitor. 

Uses of Induction coil (or Rhumkorff coil):

The induction coil has large applications like it used in automobiles, X-ray machines and discharge tubes etc. It is used to produce high voltages.

Conclusion :

The article has discussed about the concept of  Induction coil (or Rhumkorff coil). It  also provides you information related to the principle, construction, theory and uses of Induction coil (or Rhumkorff coil). I hope the concept is now clear to you. please share this on social media and help others . Thank you for your visit. 


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