Eddy Current JEE Physics Science

Eddy Current Testing (Physical Aspects)

In this article we will discuss Eddy Current Testing (Physical Aspects)

In this article, we will discuss Eddy Current Testing (Physical Aspects). So, let’s get started.

Physics aspects of ECT


• Conductivity is defined as the ability of a material to conduct electric current.
• It is denoted by σ. The unit of conductivity is mho per meter.
• The conductivity of a conductor decreases with the increase in the temperature.
• Each element has a unique value of conductivity.
• Copper, silver and gold have high conductivities where as, carbon has a very low conductivity.
• An eddy current is a flow of electrons. The amount of electron flow through an electrically conductive material is directly related to the conductivity of the material.
• If the conductivity increases, the flow of eddy current increases.


• Resistivity is reciprocal of the conductivity.
• Therefore the materials that have high resistivity have poor conductivity and vice versa.
• The resistivity is denoted by ρ and is defined as the ‘ratio of electrical intensity (emf) to the current per unit cross-section area.’
• Mathematically it can be written as ρ = E / I /A or ρ = EA/ I
• ρ = resistivity, E = emf, A = area
• The unit of resistivity is Ohm-meter.
• Resistivity of a material changes with the change in temperature.

Magnetic Permeability

• Magnetic permeability is an intrinsic property of a material.
• It is the ability of a material to concentrate magnetic lines.
• It is denoted by the Greek letter µ.
• Any material that is easily magnetized, such as soft iron,
concentrate the magnetic flux.
• This is the main feature separating magnetic materials from nonmagnetic materials.
• The magnetic permeability is equal to the induced magnetic flux density B divided by external magnetic field intensity (magnetizing force) H.
• μ = B/H ,
• Where μ = magnetic permeability, B = flux density (tesla), H = magnetizing force (amperes/metre)
•  For air, vacuum, and non-magnetic materials the μ is constant.
• The numerical values of μ for different materials are assigned in comparison with air or vacuum.
• This is called the relative permeability and is defined as μr = μ/ μ0
• Where μr = relative permeability, μ = permeability, μ0 = permeability in vacuum


• Inductance is the property of a conductor by which a change in current flowing through it induces a voltage (electromotive force) in both the conductor itself (self-inductance) and in any nearby conductors (mutual inductance).
• It is customary to use the symbol L for inductance.
• In the SI system the measurement unit for inductance is the henry (H).
• Inductive Reactance (XL), is the property in an AC circuit which opposes the change in the current.


• Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied.
• In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current (AC) circuit.


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