MAGNETIC CIRCUITS-QUESTION-ANSWERS

1) Does a magnetic circuit consume energy?

In order for setting up a magnetic flux, energy is required but no energy is required to continue it. The magnetic field holds the supplied energy and this energy is returned to the circuit when the magnetic field collapses, but finally the energy is consumed in the electric circuit.

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2) What is the reason for the leakage in magnetic circuit?

A large amount of flux is confined to the intended path in a practical magnetic circuit unfortunately there is a small amount of flux leak in the surrounding air. Leakage flux or stray flux is harmful to the electric machine.

3) There are lots of electric insulators but no magnetic insulators, Explain

As flux can be set up in the air, there is no need for magnetic insulators. There are lots of electric insulators such as air ( no current can pass through it).

4) What is the material to be selected for making electromagnets?

Energy required for demagnetizing a material of 1 m cube, varies for different materials:

1) For Soft iron: energy: 10 J/m cube

2) For Alnico, energy: 50,000 J/m cube

Electromagnets have the characteristic material to initiate small amount of energy for demagnetization.

5) Give Reason, air flux is termed as useful flux.

Air gaps are required for the rotation of rotor in case of an electric machine and for the usage in moving-coil instruments. It is a link between stationary and moving parts therefore it is a useful flux.

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6) Permeability of a material.

It is a measure of how well magnetic lines focus inside its boundaries under the magnetizing force influence. Large permeability and flux density is available in ferromagnetic material and it is greater than in a non magnetic material with similar magnetic force.

7) Difference between magnetic and electric circuit.

There is no leakage of energy in magnetic circuit and for the creation of flux, energy is required. The energy consumption is done as long as the current flows in the electric circuit and the leaked energy is given out as heat.

In a magnetic circuit, reluctance of a magnetic circuit is not stable and it depends on the flux density (B). In an electric circuit, the resistance is almost constant and its because of resistivity varies with temperature.

8) Cause of Hysteresis

1) Power loss and increase in temperature of the machine.

2) Reduces the machine competency

9) Curie Temperature

Magnetic material’s temperature increased above a certain value, curie temperature. There is a loss of magnetism in the material above this temperature and becomes paramagnetic until its temperature is lowered below this point. Curie temperature for iron: 700 degree c.

10) Hysteresis means?

It is used to describe the behavior of uncertain values with respect to the temperature changes. There are many physical phenomena associated with Hysteresis. If exact values of H are known still we cannot guess the value of B unless we know the increasing and decreasing value of both B and H.

11) Importance of magnetic circuit

It is used by transformers, generators and motors.

Loud speakers, telephone receivers, watt-hour meters, telephone ciruit also depend on magnetic flux.

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