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SYNOPSIS
B = μ_{0} nI
where n is the number of turns per unit length.
For a toriod,
where N is the total number of turns and r is the average radius.
Magnetic moment m of a planar loop carrying a current I with N closely wound turns and an area A is
Direction of is given by the right-hand thumb rule.
Right-hand thumb rule: Curl the palm of your right hand along the loop with the fingers pointing in the direction of the current. The thumb sticking out gives the direction of (and ).
When this loop is placed in a uniform magnetic field B, the force F on it is F = 0
and the torque on it is
In a moving coil galvanometer, this torque is balanced by a counter torque due to a spring yielding
kϕ = NI AB
Where ϕ is the equilibrium deflection and k is the torsion constant of the spring.
Uses of a moving coil galvanometer:
An electron moving around the central nucleus has a magnetic moment given by
Where 𝓁 is the magnitude of the angular momentum of the circulating electron about the central nucleus. The smallest value of μ_{𝓁} is called the Bohr magneton μ_{B}, and it is μ_{B} = 9.27 × 10^{–24} J/T.
Cyclotron:
A cyclotron is a device used to accelerate positively charged particles (like protons, α-particles, deuterons, ions etc.) to acquire enough energy to carry out nuclear disintegration.
A charge q executes a circular motion with frequency called the cyclotron frequency given by
This cyclotron frequency is independent of the particle’s speed and radius.
Time period
Radius
Limitations of a cyclotron:
A cyclotron cannot accelerate uncharged particles like neutrons. Positively charged particles with large mass (i.e. ions) cannot be accelerated after a certain speed in the cyclotron.
Magnetic materials tend to point in the north–south direction.
Like magnetic poles repel and unlike poles attract each other.
Cutting a bar magnet in two leads to two smaller magnets.
Magnetic poles cannot be isolated.
When a bar magnet of dipole moment is placed in a uniform magnetic field ,
Consider a bar magnet of size 𝓁 nd magnetic moment at a distance r from its midpoint, where r >>𝓁; the magnetic field due to this bar is
Gauss’s law for magnetism: The net magnetic flux through any closed surface is zero.
Curie’s law: According to Curie’s law, the susceptibility of a paramagnetic substance is inversely proportional to the absolute temperature: m = c/T, where c is a constant called the Curie constant.
The pole near the geographic north pole of the Earth is called the north magnetic pole.
The pole near the geographic south pole is called the south magnetic pole.
The magnitude of the magnetic field on the Earth’s surface = 4 × 10^{−5} T.
Three quantities are needed to specify the magnetic field of the Earth on its surface—the horizontal component, the magnetic declination and the magnetic dip.
These are known as the elements of the Earth’s magnetic field.
Consider a material placed in an external magnetic field
The magnetic intensity is defined as
The magnetisation of the material is its dipole moment per unit volume.
The magnetic field in the material is
For a linear material _{ So,}
where
𝓍: Magnetic susceptibility of the material
μ_{r}: Relative magnetic permeability
The relative magnetic permeability μr and the magnetic permeability μ are related as follows:
μ = μ_{0} μ_{r}
μ_{r} = 1 +𝓍
Magnetic materials are broadly classified as diamagnetic, paramagnetic and ferromagnetic.
For diamagnetic materials, 𝓍 is negative and small.
For paramagnetic materials, 𝓍 is positive and small.
For ferromagnetic materials, 𝓍 is positive and large.
Substances which at room temperature retain their ferromagnetic property for a long period of time are called permanent magnets.
HYSTERESIS
If a ferromagnetic material is magnetised in one direction and the applied magnetising field is removed, then its magnetisation will not be reduced to zero. It must be driven back to zero by a field in the opposite direction. If an alternating magnetic field intensity is applied to the material, its
magnetisation will trace out a loop called a hysteresis loop. The phenomenon in which magnetic flux density (B) lags behind the magnetising field (H) in a ferromagnetic material during cycles of magnetisation is called hysteresis
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Queries asked on Sunday and after 7 pm from Monday to Saturday will be answered after 12 pm the next working day.
A toroid having inner and Outer diameter with 5 centimetre and 10 centimetre carrying a current of 10 ampere if it consists 20 turns find the magnetic field due to toroid
What is dimension is magnetism