Ley De Farady

P3.4.3.1-2

Electricity
Electromagnetic induction Induction by means of a variable magnetic field

Measuring the induction voltage in a conductor loop for a variable magnetic field
Description from CASSY Lab 2 For loading examples and settings, please use the CASSY Lab 2 help.

CASSY Lab 2 (2011-06-07)

© by LD DIDACTIC GmbH · Leyboldstrasse 1 · D-50354 Huerth · www.ld-didactic.comPhome: +49-2233-604-0 · Fax: +49-2233-222 · E-mail: info@ld-didactic.de · Technical alterations reserved

CASSY Lab 2

Induction in a variable magnetic field

Alternatively (without Power-CASSY):

can also be carried out with Pocket-CASSY and Mobile-CASSY

Experiment description
Voltages and currents which are produced as a result of variations in magnetic fields are called inductionvoltages and currents, and the phenomenon itself is referred to as electromagnetic induction. When a conductor loop is placed within a magnetic field B, the magnetic flux permeating the loop is determined by the integral of the conductor loop area:

© by LD DIDACTIC GmbH · Leyboldstrasse 1 · D-50354 Huerth · www.ld-didactic.com Phone: +49-2233-604-0 · Fax: +49-2233-222 · E-mail: info@ld-didactic.de ·Technical alterations reserved

221

CASSY Lab 2
If instead of a conductor loop we use a coil with N 1 turns, all perpendicular to the magnetic field, Φ increases correspondingly to If the magnetic field B does not vary, the magnetic flux Φ remains constant. When the magnetic field, and thus the magnetic flux through the area of the coil, changes over time, a voltage and consequently acurrent as well are induced in the coil; their magnitude and direction depend on how the field varies. Faraday's law of induction applies:

and thus

Conversely, an electric current generates a magnetic field, e.g. when a current I flows through a coil. For the magnetic field inside a large cylindrical coil with the length L and the number of turns N 2, the following applies:

where

0

=4π·10 Vs/Am (magnetic field constant).

-7

This experiment uses a large cylindrical coil as a field coil through which a varying current I(t) flows, which generates a varying magnetic field B(t) within the coil. Rectangular induction coils having different cross-sections (areas) A and numbers of turns N1 are placed inside this field coil. A voltage U is induced in these coils, which can becalculated as:

This experiment verifies the proportionalities between the induced voltage U and the change over time dI/dt of the field-coil current I, the area A of the induction coils and the number of turns N1 of the induction coils. Power-CASSY (524 011) or the triangular wave form power supply (521 56) are particularly suitable for this experiment, as the output current I over time can becontrolled so that the slope | dI/dt | is constant. The slope | dI/dt | is continuously adjustable from 0.2 A/s to 2.2 A/s. Three induction coils are also provided, with N 1 = 300 turns each. Coil 1 has the 2 2 2 cross-section A = 50 × 50 mm , coil 2 A = 30 × 50 mm and coil 3 A = 20 × 50 mm . Coil 1 is also provided with additional taps at N1 = 100 and N1 = 200 turns.

Equipment list
1 1 1 1 1 1 1 22 1 Sensor-CASSY Power-CASSY CASSY Lab 2 V box Field coil, d = 120 mm Stand for tubes and coils Set of induction coils Connecting leads, 100 cm, red Connecting leads, 100 cm, blue PC with Windows XP/Vista/7 524 010 or 524 013 524 011 524 220 524 040 516 244 516 249 516 241 501 30 501 31

Alternatively (without Power-CASSY) 1 Sensor-CASSY 1 CASSY Lab 2 1 V box 1 30-A box 1 Field coil, d = 120 mm1 Stand for tubes and coils 1 Set of induction coils 1 Triangular wave form power supply 1 Connecting lead, 50 cm, blue 2 Connecting leads, 100 cm, red 2 Connecting leads, 100 cm, blue 1 PC with Windows XP/Vista/7

524 010 or 524 013 524 220 524 040 524 043 516 244 516 249 516 241 521 56 501 26 501 30 501 31

© by LD DIDACTIC GmbH · Leyboldstrasse 1 · D-50354 Huerth · www.ld-didactic.com...