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AGH University of Science and Technology in Cracow

Department of Electronics

Laboratory Manual Physics_1

Title:

Self-inductance of coils 2011 r.

Experiment

No.

7

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1. Goal To find the inductance L of a coil by comparison of the coil impedance in an AC circuit and

the coil resistance in a DC circuit.

2. What you need to learn? Capacitance. Faraday's Law of Induction. Lenz's Law. Definition of the inductance. The SI-

unit of the inductance. Self-induced emf. Magnetic energy stored by an inductor. Inductors in

DC circuits. Inductors in AC circuits. Inductive reactance XL. Impedance Z. Conductance G.

Inductive susceptance B. Admittance Y. Phase shift between the voltage and the current in RL

circuits. Hysteresis loop of a ferromagnetic.

3. Equipment The measurement set up is shown in Fig. 1. It consists of a DC/AC power supply, a wire-

wound rheostat, a digital voltmeter, a digital ammeter and a coil.

Fig. 1. Measurement set-up

Two types of coils are investigated by measurements of current flowing through coils in

function of voltage applied to the coil terminals. Voltage applied to the coil terminals is

controlled by the wire-wound rheostat with a movable wiper. Digital voltmeters and

ammeters have both AC and DC settings. They also have buttons that allow the user to choose

the appropriate range for the voltage or current that are to be measured. DC/AC power supply

is available. The two coils - number 1 and number 2 - are wounded on the common core.

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4. Measurements 1. Set-up a circuit as it is shown in Fig. 1. Connect the Coil 1. Set the digital voltmeter

and the digital ammeter for DC operation in the range 20V and 2A, respectively.

2. Turn on the DC voltage supply. Moving the wiper across the wire-wound rheostat,

change the voltage applied to the coil in the range 0÷12 V. Measure the voltage drop

across the coil U and measure current through the coil I. Collect about 10 – 15

measurements in order to determine characteristic I =(U=). Record the results in

Tab.1.

Table 1. DC circuit .

Coil 1 No. U [V] I [mA] I [A]

3. Turn off the DC voltage supply. Disconnect the coil 1 and connect the coil 2. For the

coil 2 repeat the procedure described in point 2.

4. Now use the AC voltage supply. Set the digital voltmeter and the digital ammeter for

AC operation. Make the correction of the ammeter range. Due to the capacitive

reactance, the lower range of current is necessary.

5. Measure characteristics I~ (U~) for the coil 1 and the coil 2. Record the results in

Tab.2 .

Table 2. AC circuit.

Coil 2 No. U [V] I [mA] I [A]

Coil 2 No. U [V] I [mA] I [A]

5. Data Handling 1. Draw plots I =(U=) and I~ (U~) for the coil 1 and coil 2 in one rectangular coordinates.

Coil 2 No. U [V] I [mA] I [A]

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2. Fit the experimental points to the linear function UGUI ⋅=)( where G is conductance for the DC circuit or admittance for the AC circuit. Use the method of linear regression

3. On the basis of calculated conductance and admittance, determine the resistance R and inductive reactance XL of a coil.

4. When you know frequency f of voltage changes and have inductive reactance XL calculated, find inductance L of a coil and its uncertainty ΔL.

5. Finally calculate the tangent of the phase angle : RLtg ωδ = and the phase angle δ

(in degrees)

Literature:

1. Halliday, Resnick “Fundamentals of Physics - 8th edition”, John Wiley 2007,

2. Zięba “Pracownia Fizyczna Wydziału Fizyki I Techniki Jądrowej AGH”, Uczelniane Wydawnictwo Naukowo-Dydaktyczne 1999.

Updated: 28.02.2011 by Barbara Dziurdzia