3B Scientific Pohl's Torsion Pendulum - Manual (Page 5)

10
• After measuring the period T the natural frequency
of the system
ω
0
can be obtained from
ω
0
= 2
π/T = 3.3069 Hz
• The most extreme deflection arises at a motor volt-
age of 7.6 V, i.e. the resonance case occurs.
• Then the same experiment is performed with an
eddy current brake connected at currents of
Ι = 0.2 A, 0.4 A and 0.6 A.
ΙΙΙΙΙ = 0.2 A
Motor voltage V
ϕ
3.0 0.9
4.0 1.1
5.0 1.2
6.0 1.7
7.0 2.9
7.6 15.2
8.0 4.3
9.0 1.8
10.0 1.1
ΙΙΙΙΙ = 0.4 A
Motor voltage V
ϕ
3.0 0.9
4.0 1.1
5.0 1.3
6.0 1.8
7.0 3.6
7.6 7.4
8.0 3.6
9.0 1.6
10.0 1.0
ΙΙΙΙΙ = 0.6 A
Motor voltage V
ϕ
3.0 0.9
4.0 1.1
5.0 1.2
6.0 1.6
7.0 2.8
7.6.0 3.6
8.0 2.6
9.0 1.3
10.0 1.0
• From these measurements the resonance curves can
be plotted in a graph depicting the amplitudes
against the motor voltage.
• The resonant frequency can be determined by find-
ing the half-width value from the graph.
Resonance curves
1
5
10
15
20
A
[skt]
0 1 2 3 4 5 6 7 8 9 10
I=0,0A
I=0,2A
I=0,4A
I=0,6A
u[v]
3B Scientific GmbH • Rudorffweg 8 • 21031 Hamburg • Germany • www.3bscientific.com • Technical amendments may occur