Lab Title: Determination of Magnetic Permeability Using BH Curve

Objectives:

  • To plot the BH curve (magnetic flux density vs. magnetic field intensity) for a given magnetic material
  • To determine the relative permeability of the magnetic material
  • To understand magnetic hysteresis behavior
  • To identify key magnetic parameters like retentivity and coercivity

Materials and Equipment:

  • Iron ring core/toroid core specimen
  • Primary winding (magnetizing coil)
  • Secondary winding (search coil)
  • Ammeter (0-5A)
  • Ballistic galvanometer
  • Rheostat (0-100Ω)
  • Battery/DC power supply
  • DPDT switch
  • Connecting wires
  • Graph paper

Theory

The magnetic permeability (μ) of a material describes how easily it can be magnetized in response to a magnetic field. It is defined as the ratio of magnetic flux density (B) to the magnetic field intensity (H):

μ = B/H

Where:

  • B is measured in Tesla (T)
  • H is measured in Ampere per meter (A/m)
  • μ is measured in Henry per meter (H/m)

Key Equations:

  1. Magnetic field intensity (H) = (N₁I)/l

    • N₁ = number of turns in primary coil
    • I = current in primary coil
    • l = mean length of magnetic path

  2. Magnetic flux density (B) = (K × Î¸)/A

    • K = ballistic galvanometer constant
    • θ = ballistic throw
    • A = cross-sectional area of specimen

Experimental Setup


 


  1. Wind primary and secondary coils on the iron ring specimen
  2. Connect the primary circuit with ammeter, rheostat, and DPDT switch
  3. Connect the secondary circuit to the ballistic galvanometer

 Procedure

  1. Initial Setup

    • Record the specifications of the specimen (dimensions, number of turns)
    • Note the ballistic galvanometer constant
    • Ensure all connections are secure

  2. Data Collection
    a. Forward Magnetization

    • Starting from zero, increase current in steps of 0.2A
    • Record galvanometer deflection for each step
    • Continue until magnetic saturation is reached

    b. Reverse Magnetization

    • Decrease current to zero
    • Reverse current direction using DPDT switch
    • Record readings while increasing current in opposite direction
    • Continue until negative saturation

    c. Complete Cycle

    • Repeat process in reverse direction to complete the hysteresis loop
Data Recording



 Calculations

  1. Calculate H values using H = (N₁I)/l
  2. Calculate B values using B = (K × Î¸)/A
  3. Calculate permeability (μ) at different points using μ = B/H
  4. Plot the BH curve using the collected data

Expected Graph

The BH curve should show:


 Analysis Questions

  1. What is the maximum relative permeability of the material?
  2. At what field strength does magnetic saturation occur?
  3. Explain the significance of the area within the hysteresis loop.
  4. How does the shape of the curve indicate whether the material is magnetically soft or hard?
  5. Calculate the energy loss per cycle from the hysteresis loop.

Sources of Error

  • Non-uniform winding of coils
  • Temperature variations
  • Measurement uncertainties in current and deflection readings
  • Residual magnetism in the specimen

Safety Precautions

  • Do not exceed the maximum current rating of the coils
  • Ensure proper insulation of all connections
  • Handle the ballistic galvanometer with care
  • Keep magnetic materials away from the setup

Conclusion