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  • EE - 109 Inductor and Inductance Experiments

    The inductance measurements in coils and the effect of iron core to inductance

    Possible Experiments
    • The measurement of self inductance of coils,
    • Self inductance of coils with iron core
    Standard Equipment

    DC power supply, ampermeter, voltmeter, 12ohm resistor, 2 coils, 1 coil with iron core, function generator, connection cables. The coils have radii of 20 mm and their length is 14 cm...

    Technical Information

    The circuits with coils behave differently to DC and Ac signals. They show an impedence (Z) to AC current. A coil to which an AC potential is shown in the figure. From this circuit one can write: VAC=VAB+VBC where VAC= L dI/dt + R I  where I is current, dI/dt is its change, L is the inductance and R is the resistance. The reaktans: XL=wL is a function of the angular frequency given by w=2πf with frequency: f. On a circuit with inductance, the voltages across resistor and coils have 90o phase difference but the current through the resistor has the same phase with the voltage. If VL is the inductance voltage, and VR is the resistor voltage, their vector sum gives: Z2=I L2w2 + R2 . If R is measured by a multimeter, and Z is obtained from I-V graph, one can easily calculate L. Note that the self inductance of the cylindrical coil is L00 A N2/L where N is the number of windings, A is cross section area, L is the length and μ0 = 4πx10-7 H/m is the magnetic permeability of air. If an iron core is inserted thrugh the centerline of the coil, the inductance increases to L=μL0 where μ is the magnetic permeability of iron.

    The serial coil filters high frequencies (low pass filter). This property can be examined by applying signals with different frequencies from the function generator and measuring the ratio of input and output voltages.