Physics MAGNETIC INDUCTION AND INTENSITY OF MAGNETIZATION

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MAGNETIC INDUCTION AND INTENSITY OF MAGNETIZATION

Magnetic Induction

Under some circumstances, a magnetic field can create an electric voltage, or an electric current. This phenomenon is called magnetic induction. It always involves change or motion of some sort. A conductor which moves perpendicular to a magnetic field will set up an electric potential difference between its ends, of size

`V=vLBsintheta`

where `v` is the velocity of the conductor, `L` is its length, `B` is the strength of the magnetic field, and theta is the angle between the velocity of the conductor and the direction of the magnetic field.

If an induced voltage is applied to an electric circuit, it can cause an induced current to flow through the circuit. Any work done by an induced current is taken from the kinetic energy of the moving conductor; one must apply a constant force to the conductor to keep it moving at a constant speed.

Under some circumstances, a magnetic field can create an electric voltage, or an electric current. This phenomenon is called magnetic induction. It always involves change or motion of some sort. A conductor which moves perpendicular to a magnetic field will set up an electric potential difference between its ends, of size

`V=vLBsintheta`

where `v` is the velocity of the conductor, `L` is its length, `B` is the strength of the magnetic field, and theta is the angle between the velocity of the conductor and the direction of the magnetic field.

If an induced voltage is applied to an electric circuit, it can cause an induced current to flow through the circuit. Any work done by an induced current is taken from the kinetic energy of the moving conductor; one must apply a constant force to the conductor to keep it moving at a constant speed.

Magnetization

We have seen that a circulating electron in an atom has a magnetic moment. In a bulk material, these moments add up vectorially and they can give a net magnetic moment which is non-zero. We define magnetization `M` of a sample to be equal to its net magnetic moment per unit volume:

`M=(m_(n e t))/V`

M is a vector with dimensions `[L^(-1) A]` and is measured in a units of `A m^(-1)`.

Consider a long solenoid of `n` turns per unit length and carrying a current `I`. The magnetic field in the interior of the solenoid given by

`B_0=mu_0nI`

If the interior of the solenoid is filled with a material with non-zero magnetization, the field inside the solenoid will be greater than `B_0`. The net B field in the interior of the solenoid may be expressed as

`B=B_0 + B_m`

where `B_m` is the field contributed by the material core. It turns out that this additional field `B_m` is proportional to the magnetization M of the material and is expressed as

`B_m = mu_0 M`

where `mu_0` is the same constant (permeability of vacuum) that appears in Biot-Savart-s law.

We have seen that a circulating electron in an atom has a magnetic moment. In a bulk material, these moments add up vectorially and they can give a net magnetic moment which is non-zero. We define magnetization `M` of a sample to be equal to its net magnetic moment per unit volume:

`M=(m_(n e t))/V`

M is a vector with dimensions `[L^(-1) A]` and is measured in a units of `A m^(-1)`.

Consider a long solenoid of `n` turns per unit length and carrying a current `I`. The magnetic field in the interior of the solenoid given by

`B_0=mu_0nI`

If the interior of the solenoid is filled with a material with non-zero magnetization, the field inside the solenoid will be greater than `B_0`. The net B field in the interior of the solenoid may be expressed as

`B=B_0 + B_m`

where `B_m` is the field contributed by the material core. It turns out that this additional field `B_m` is proportional to the magnetization M of the material and is expressed as

`B_m = mu_0 M`

where `mu_0` is the same constant (permeability of vacuum) that appears in Biot-Savart-s law.

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