To study the factors affecting self inductance of a coil when connected in series with a resistor/bulb in a circuit connected by an AC source of variable frequency?pls help me

observation of project on self inductance for class 12

Factors of self induction......
Orested statement

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project on factors affecting self inductance of a coil

There are four basic factors of inductor construction determining the amount of inductance created. These factors all dictate inductance by affecting how much magnetic field flux will develop for a given amount of magnetic field force (current through the inductor’s wire coil):

NUMBER OF WIRE WRAPS, OR “TURNS” IN THE COIL: All other factors being equal, a greater number of turns of wire in the coil results in greater inductance; fewer turns of wire in the coil results in less inductance.

Explanation: More turns of wire means that the coil will generate a greater amount of magnetic field force (measured in amp-turns!), for a given amount of coil current.


COIL AREA: All other factors being equal, greater coil area (as measured looking lengthwise through the coil, at the cross-section of the core) results in greater inductance; less coil area results in less inductance.

Explanation: Greater coil area presents less opposition to the formation of magnetic field flux, for a given amount of field force (amp-turns).


COIL LENGTH: All other factors being equal, the longer the coil’s length, the less inductance; the shorter the coil’s length, the greater the inductance.

Explanation: A longer path for the magnetic field flux to take results in more opposition to the formation of that flux for any given amount of field force (amp-turns).



CORE MATERIAL: All other factors being equal, the greater the magnetic permeability of the core which the coil is wrapped around, the greater the inductance; the less the permeability of the core, the less the inductance.

Explanation: A core material with greater magnetic permeability results in greater magnetic field flux for any given amount of field force (amp-turns).


An approximation of inductance for any coil of wire can be found with this formula:


It must be understood that this formula yields approximate figures only. One reason for this is the fact that permeability changes as the field intensity varies (remember the nonlinear “B/H” curves for different materials). Obviously, if permeability (µ) in the equation is unstable, then the inductance (L) will also be unstable to some degree as the current through the coil changes in magnitude. If the hysteresis of the core material is significant, this will also have strange effects on the inductance of the coil. Inductor designers try to minimize these effects by designing the core in such a way that its flux density never approaches saturation levels, and so the inductor operates in a more linear portion of the B/H curve.

If an inductor is designed so that any one of these factors may be varied at will, its inductance will correspondingly vary. Variable inductors are usually made by providing a way to vary the number of wire turns in use at any given time, or by varying the core material (a sliding core that can be moved in and out of the coil).

Inductance
A current generated in a conductor by a changing magnetic field is proportional to the rate of change of the magnetic field. This effect is called INDUCTANCE and is given the symbol L. It is measured in units called the henry (H) named after the American Physicist Joseph Henry (1797-1878). One henry is the amount of inductance required to produce an emf of 1 volt in a conductor when the current in the conductor changes at the rate of 1 Ampere per second. The Henry is a rather large unit for use in electronics, with the milli-henry (mH) and micro-henry (µH) being more common. These units describe one thousandth and one millionth of a henry respectively.
Although the henry is given the symbol (capital)H the name henry, applied to the unit of inductance uses a lower case h. The plural form of the henry may be henries or henrys; the American National Institute of Standards and Technology recommends that in US publications henries is used.
Factors Affecting Inductance.
The amount of inductance in an inductor is dependent on:
a. The number of turns of wire in the inductor.
b. The material of the core.
c. The shape and size of the core.
d. The shape, size and arrangement of the wire making up the coils.
Because inductance (in henries) depends on so many variable quantities, it is quite difficult to calculate accurately; numerous formulae have been developed to take different design features into account. Also these formulae often need to use special constants and tables of conversion data to work with the required degree of accuracy. The use of computer programs and computer-aided design has eased the situation somewhat. However, external effects caused by other components and wiring near the inductor, can also affect its value of inductance once it is assembled in a circuit, so when an accurate value of inductance is required, one approach is to calculate an approximate value, and design the inductor so that it is adjustable.
A typical formula for approximating the inductance value of an inductor is given below. This particular version is designed to calculate the inductance of "A solenoid wound with a single layer of turns of infinitely thin tape rather than wire, and with the turns evenly and closely spaced."

INDUCTORS AND INDUCTANCE

Capacitors are capable of storing a charge in an electrostatic field. Inductors are capable of storing a charge in an electromagnetic field.

The ability to induce a voltage across itself with a change in current is known as self-inductance or simply inductance. Inductance also opposes a change in current.

Inductors have no opposition to steady DC.

L is the symbol for inductance. The basic unit of inductance is H henry named after the American physicist Joseph Henry.

Inductance in electrical circuits is similar to inertia in mechanical operations. It requires more energy to start or stop current in an inductor than it does to keep it flowing.

INDUCTOR BASICS

An inductor is a coil of wire. A coil of wire is an electromagnetic when current is passed through it.

Inductors are also called chokes, impedance coils, and reactors.

The core of an inductor may be a magnetic material such as iron or an insulated material. The term air-core is used for any inductors that do not have a magnetic core.

Inductance is greater with more coils, larger cross-sectional area, and shorter coil length.

SELF-INDUCTANCE

Any conductor has some inductance because it produces a magnetic field around it. When the current changes the magnetic field changes. When the magnetic field changes an electromotive force is induced in the conductor. The polarity of this induced force is in the opposite to the applied voltage of the conductor. The effect is that inductance opposes a change in current magnitude.

Lenz’s law states this. The induced emf in any circuit is always in a direction to oppose the effect that produced it.

When AC (Alternating Current) is passed through an inductor there is a continuous change in current. The effect of the opposition to current is then continuous.

When DC (Direct Current) is passed through an inductor the opposition to current is only present when there is a change, such as starting, stopping, or a change in current flow.

The Self-Induced Voltage Equation

1 H (Henry) of inductance is seen when a change in current of 1A per second causes an induced voltage of 1V.

FACTORS AFFECTING COIL INDUCTANCE


Greater number of turns increases inductance
A larger diameter coil has greater inductance
Inductance decreases as the coil length increases
A high permeability core increases inductance

The Inductance Equation
L = (uN2A/l)

MUTUAL INDUCTANCE

Mutual inductance is when two coils are located so that the magnetic flux from one coil links with the turns of another coil. The coils are referred to as coupled.

The transformer for AC circuits is a common example of mutual inductance.

Factors Affecting Mutual Inductance
Tight coupling refers to a high degree of mutual inductance such as a transformer with two coils wound around the same magnetic core.

Loose coupling is when two coils are far apart or at right angles to each other.

Air Core
Coils with hollow or non-magnetic cores are called Air-core coils. They have low values of inductance and are generally used for high-frequency applications.

Iron Core
Iron-core inductors use iron or an alloy for a core. Large values of inductance are possible. Hysteresis and eddy-current losses limit iron-core to low frequencies such as power line and audio. Laminated sheet material is often used to reduce eddy currents. Soft iron material such as silicon steel may be used to reduce hysteresis losses.

Powdered-Iron Core
Powdered-iron is mixed with a nonconductive binder reduce eddy current losses. Higher current flow is possible before the inductor saturates.

Ferrite Core
Ferrites are good magnetic conductors but poor electrical conductors. This reduces eddy current losses.

Toroidal Core
Because of the shape most of the flux flows within the core resulting in very little flux leakage loss.

Movable (Variable) Core
These are variable inductors which can be turned.

Printed Circuit Board Core
A spiral of copper on a printed circuit board may be used as a coil. Only small inductance values are possible which limits its usefulness to high frequency applications.

INDUCTOR COMBINATIONS

Inductors in Series

When inductance are not coupled (far enough apart to not influence each other) and connected in series the total inductance is the sum of the individual inductances.

LT = L1 + L2 + L3 + … + LN

When two mutually coupled coils are connected in series the total inductance is affected by their fields either series-aiding or series-opposing each other.

LT = L1 + L2 +/- 2LM

Inductors in Parallel

When inductors are not coupled and connected in parallel the total inductance is found in a similar manner to total resistance of resistors in parallel.

LT = 1 / ( 1/L1 + 1/L2 + … + 1/LN)

Mutually coupled inductors in parallel:

Aiding fields: 1/LT = 1 / (L1 + LM) + 1 / (L2 + LM)

Opposing fields: 1/LT = 1 / (L1 - LM) + 1 / (L2 - LM)

ENERGY STORED IN AN INDUCTOR

Opening the Circuit

When a circuit with an inductor is opened the magnetic field collapses and voltage is induced. The voltage dissipates over time due to I2R loss.

STRAY INDUCTANCE

All conductors in a circuit possess some inductance. At high frequencies stray inductance can become significant.

To reduce stray inductance lead lengths should be kept short. Carbon resistors are preferred over wire-wound resistors. However, some wire-wound resistors are made non-inductive by winding adjacent so that the magnetic fields cancel each other.

INDUCTOR LOSSES AND FAULTS

Inductor Losses

Inductor losses are hysteresis and eddy currents.

Flux-leakage is another type of loss. This is magnetic flux outside the path for which it will do useful work.

Skin effect is another cause for loss. Most of the current flows along the outside of the conductor or skin. Hollow wire can be used to minimize the skin effect.

Troubleshooting Inductor Faults

Inductors can change value (including open) and shorts can develop between windings.

Shorts cannot normally be detected with ohmmeters because the change in resistance is so small. A ringing test can be used which creates a magnetic field and then checks the number of rings as the field collapses.