Mutual Induction Experiment 56615q

AIM TO STUDY MUTUAL INDUCTION

INTRODUCTION Self-induction in coil or conductor is actually an induced back emf, which is generated when the magnetic field caused by the current flow cuts the coil or conductor. If the flux lines from the expanding and contracting magnetic field of one coil were to cut the windings of another nearby coil, a voltage would also be induced in that coil. The amount of emf induced in this way depends on the relative positions of the two coils. Also, the more turns of the second coil that are induced. This inducing of an emf in a coil or conductor by magnetic flux lines generated in another coil or conductor is called the primary, or primary winding, and the one in which the emf is induced is called the secondary. Similarly, the current that flows through the primary is the primary current, and if the secondary is connected to a load so that current flows, this current is called secondary current.

When current flows in the secondary, it sets u its own magnetic field, which induces a voltage back into the primary winding. Thus, when mutual induction occurs between two coils, there are four voltages present. These are (1) are applied voltage in the primary, (2) the self-induced emf in the primary, (3) the induced emf in the secondary, and (4) the emf induced back into the primary by the secondary current. Therefore, the actual or effective overall, inductance of two coils that are mutually coupled is complex because of the complex interactions between the magnetic fields. This effective inductance of two coils that are mutually coupled is called mutual inductance.

MUTUAL INDUCTANCE Mutual inductance can be considered as the amount or degree of mutual induction that exists between two coils or winding. The mutual inductance of any two coils depends on the flux linkage between the coils, which is turn depends on their positions relative to each other. The degree of flux linkage is expressed by a factor called the coefficient of coupling. When all of the flux lines from each coil cut, or link, the other coil, the coefficient of coupling is 1, which is maximum value. If only some of the flux lines from each coil cut the other, the coefficient of coupling has some value less than 1. You can see then that when no mutual inductance exists between two coils, the coefficient of coupling is close to 1, the two coils are said to have tight coupling; and when the value is much less than 1, the coils have loose coupling. The term critical coupling is used to describe line between loose the tight coupling.

When the coefficient of coupling between two coils is known, the total inductance of the coils is found by multiplying the values of inductance of the coils, taking the square root of the result, and multiplying it by the coefficient of coupling. As an equation, this is given by: M = k - L1 X L2 Where M is the total inductance of the mutually coupled coils, in henrys; k is the coefficient of coupling; and L 1 and L 2 are the individual inductances of the coils, in henrys.

THE TRANSFORMER When mutual induction exists between two coils or windings, a change in current through one induces a voltage in the other. Devices which make use of this principle are called transformer. Every transformer has a primary winding and one or more secondary windings. The primary winding receives electrical energy from a power source and couples this energy to the secondary winding by means of a changing magnetic field. The energy appears as an emf across the secondary winding, and if a load is connected to the secondary, the energy is transferred to the load. By means of transformers, electrical energy can be transferred from one circuit to another, with no physical connection between the two. The transformer thus acts as a coupling device. Transformers are also indispensable in a-c power distribution, since they can convert electrical power at a given current and voltage into the equivalent power at some other current and voltage.

TRANSFORMER OPERATION WITH OPEN SECONDARY You will that when mutual induction exists between two coils, not only does the current in the primary coil induce a voltage in the secondary coil, but the resulting current in the secondary coil, in turn, induces a voltage back into the primary coil. This occurs in a transformer, and it is in large part responsible for how a transformer works. However, for ease of understanding, transformer having an open secondary. No current flows in the secondary in this case, and so no voltage is induced back into the primary. After the description of how a transformer with an open secondary works, a complete transformer, with current flowing in both the primary and the secondary, will be described. In a transformer having an open secondary, the primary operates essentially the same as an inductor. This means that the primary current lags the applied voltage by 90 degrees and at the same time lead the back emf are thus of opposite polarity. Most transformers are designed to have large back emf’s in the primary when the secondary is open, so the primary current is therefore very low. As the magnetic field around the primary winding, caused by the changing current current through the primary, alternately expands and collapses, it cuts the turns of the secondary winding, thereby inducing a voltage in the secondary. The voltage induced in the secondary is maximum when the rate of change of the primary current is greatest (0, 180, and 360 degrees), and zero when the primary current is not changing (90 and 270 degrees). When this relationship is plotted, that the secondary voltage lags the primary current by 90 degrees. Since the primary applied voltage leads the primary current, the secondary voltage is therefore 180 degrees out of phase with the primary voltage. It is also in phase with the back emf in the primary.

Usually, the letter T designates a transformer, with P as the primary, and S as the secondary, or secondaries.

Sometimes, dots are used to indicate the in-phase terminal of the two windings. The schematic symbols alone do not show phase relationships because external wires can be crossed to make the output in phase with the input.

OBSERVATION & WORKING In this given model of Mutual Induction we observe that step down transformer provides 6V ac to Ist coil connected directly to it. It provides the source voltage to this coil. The second coil, identical to the first coil, is not physically or electrically connected to coil-1 (primary). The primary flux is providing a source induce voltage to coil-2 (Secondary) due to Mutual Induction & LED connected to it will lit up. The distance between coil-1&2 changes the intensity of LED.

COMPONENT USED

4.

1.

Step down Transformer 6V dc ...................... 1

2.

Ferrite Rods with enamelled ........................ 2 coil windings (200 turns each)

3.

Light Emitting Diode.....................................1 Main Cord, wires, spares etc .........................1

MUTUAL INDUCTION INTRODUCTION : Self-induction in coil or conductor is actually an induced back emf, which is generated when the magnetic field caused by the current flow cuts the coil or conductor. If the flux lines from the expanding and contracting magnetic field of one coil were to cut the windings of another nearby coil, a voltage would also be induced in that coil. The amount of emf induced in this way depends on the relative positions of the two coils. Also, the more turns of the second coil that are induced. This inducing of an emf in a coil or conductor by magnetic flux lines generated in another coil or conductor is called the primary, or primary winding, and the one in which the emf is induced is called the secondary. Similarly, the current that flows through the primary is the primary current, and if the secondary is connected to a load so that current flows, this current is called secondary current. When current flows in the secondary, it sets u its own magnetic field, which induces a voltage back into the primary winding. Thus, when mutual induction occurs between two coils, there are four voltages present. These are (1) are applied voltage in the primary, (2) the selfinduced emf in the primary, (3) the induced emf in the secondary, and (4) the emf induced back into the primary by the secondary current. Therefore, the actual or effective overall, inductance of two coils that are mutually coupled is complex because of the complex interactions between the magnetic fields. This effective inductance of two coils that are mutually coupled is called mutual inductance. OBSERVATION & WORKING : In this given model of Mutual Induction we observe that step dowN transformer provides 6V ac to Ist coil connected directly to it. It provides the source voltage to this coil. The second coil, identical to the first coil, is not physically or electrically connected to coil-1 (primary). The primary flux is providing a source induce voltage to coil-2 (Secondary) due to Mutual Induction & LED connected to it will lit up. The distance between coil-1&2 changes the intensity of LED. COMPONENT USED : 1.Step down Transformer 6V dc 1 2.Ferrite Rods with enameled 2 coil windings (200 turns each) 3.Light Emitting Diode 1 4.Main Cord, wires, spares etc. 1