Lascells Ltd.,
Walkmill Business Park, Sutton Road, Market Drayton, Shropshire. TF9 2HT
Tel: 01630 657801 Fax: 01630 656726
Visit us at www.lascells.com
USING A SIGNAL GENERATOR
A signal generator provides a variable a.c. signal which is converted into longi-
tudinal waves by the loudspeaker. Longitudinal waves consist of low and high
pressure areas and these give pressure differences at the gas flames controlling
their height.
Best results are obtained when there is a stationary wave in the tube. For this to
occur the tube length has to relate to the signal frequency so that waves are re-
flected from each end of the tube in such a way that constructive interference
occurs and nodes and antinodes occur in fixed positions.
The wavelength can be determined by measuring the distance between nodes or
anti-nodes (see diagram below) and the speed of sound in gas determined from
the equation v = f.
l/4
l/2
Flame Height
Adjust the frequency of the source to get a good stationary wave with three or
four nodes visible. For
about 60 cm and v = 300ms
-1
the frequency is in the
region of 500Hz.
Actual waves are longitudi-
nal not transverse.
