Precautions Keep the tension in the wire constant throughout this experiment, as frequency varies with tension and it is assumed all other variables are kept constant.
Place the paper rider at the midpoint between the two bridges.This is where the antinode will be. Repeat and find an average length at each frequency. Take care to avoid parallax error when using the metre stick.
Note A pulley,scale pan and Newton weights can be used instead of the Newton balance and tension control key.
Note
A signal generator and magnet can be used instead of tuning forks. The frequency is varied by adjusting the signal generator and taking readings from it. Fig 11.19 illustrates the different apparatus.
Tension control key
Signal generator
U-shaped Paper rider magnet
l
Fixed bridge Sonometer
Safety Precaution Wear safety goggles in case the sonometer wire snaps.
MANDATORY EXPERIMENT 14
Investigation of the Variation of Fundamental Frequency of a Stretched String with Tension
Apparatus Sonometer, paper rider, Newton balance and tension control key, tuning forks
Procedure Set up apparatus as illustrated in Fig 11.20. Strike the tuning fork of highest frequency and position it on the fixed bridge.The frequency of the tuning fork is written on it. (T)
(f )
Vary the tension of the wire , by adjusting the tension control key until resonance occurs.
Tension control key
Tuning fork Paper rider Newton balance Fig 11.19
Movable bridge Newton weights
Sonometer Fixed bridge
The paper rider will jump off the wire when resonance occurs. Measure the tension using the Newton balance.
Repeat the process using tuning forks of different frequencies so as to get six or seven readings.
