Lab Manual: Sound | Lab Manuals for Class 9 PDF Download

Objective

Theory

• Sound: It is a form of energy produced by vibration and it needs medium to propagate.
• Reflection of sound: As light reflects when it strikes any hard object (opaque), sound also gets reflected when it strikes any object.

1. The angle of incidence is always equal to the angle of reflection.
2. The incident sound wave, the normal and the reflected sound wave lie in the same plane.
   

Materials Required

Procedure

• Fix the white sheet on drawing board with thumb pin.
• Draw a line AB to place the metal plate as reflecting surface with the help of metal stand, and draw normal OP to this line as shown in the figure.
• Now draw a line OC making an angle of 30° with the line OP.
• Place one metal tube near to the point O of normal and metal plate on the line OC.
• Place the ticking watch closer to one end of this metal tube.
• Now place the second tube so that its one end is near to the point O. Bring your ear close to the other end and adjust its position such that it collects the maximum reflected sound.
  
• Mark the position of the tube when it collects the clear and maximum reflected sound.
• Draw an extended line of reflected sound wave and mark it as OD.
• Measure the angle of incidence and the angle of reflection.
• Follow the above procedure and record your observation thrice.
  

1. The angle of incidence is equal to the angle of reflection.
2. The incident, normal and reflected sound waves lie in the same plane.

Precautions

• The metal plate should be placed vertical on the drawing board.
• Both the pipes used should be clean and shining.
• The sound producer i.e. stopwatch should be placed closer to the end of the metallic tube.
• Avoid touching of the source of sound to the metal tube.
• Maintain complete silence in the lab.