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Unformatted text preview: PHY134 - Classical Physics II Laboratory Induction In part I of this experiment, the voltage induced in a coil of wire by a changing magnetic flux will be observed. In part II, the magnetic field along the axis of a current loop will be precisely measured. Equipment Oscilloscope, Set of induction coils, and large loop coil, Oscillator, Probe coil with amplifier, DC power supply, Tap Switch, Galvanometer, Bar magnet, Magnetic compass. Method In part I, a galvanometer G is connected to the terminals of an induction coil (the larger of the pair) as shown below. A magnetic field is produced by a bar magnet (Fig. 1a) or by a second coil set up inside the larger coil (Fig. 1b). The currents induced in the larger coil as the field changes are observed with the galvanometer. The magnetic field produced by a current loop will be measured with a probe coil. The dependence of the magnetic field on the distance x will be compared with the formula derived in the textbook. The basic setup is shown in Figure 2. The large coil, which is connected to an oscillator (function generator), produces a time-varying magnetic field. This field induces a voltage in the small probe coil proportional to the strength of the field. An oscilloscope is used to measure the signal induced in the probe coil. A coil carrying an AC current i = i 0 sin( t ) of (angular) frequency produces a time-varying magnetic field. The field along the coil axis is given by: B ( x ) = Ni a / [2( a 2 + x 2 ) 3/2 ] sin( t ) = Ni / [2a(1+ x 2 / a 2 ) 3/2 ] sin( t ) = B ( x ) sin( t ), where B ( x ) = [ Ni / (2a)] (1+ x 2 / a 2 )- 3/2 , (1) and x is the distance from the measuring point to the center of the large coil, a is the coil radius, N is the number of turns of the large coil, and is the permeability constant of free space. The voltage induced in the probe coil at position x is: V ( t ) = emf = N probe A probe dB / dt = N probe A probe B ( x ) cos( t ) = V ( x ) cos( t ), where V ( x ) = N probe A probe B ( x ) (2) is the amplitude of the induced voltage at position...
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