WAVES

1. 
   where c is the speed of a wave, f is its frequency and  is its wavelength.
2. 
   where f’ is the observed frequency, f is the actual frequency, c is the speed of the wave and v is the speed of the source.
   (Note: Take minus for approaching waves and plus for receding waves.)
3. 
   where I is sound intensity, P is power and A is an area at right angles to the direction of the sound at that point.
4. 
   where f is the fundamental frequency, l the length, T the tension and  the mass per unit length of a stretched string.
5. To measure the speed of air using a resonance tube:
   
6. or
   where d is the distance between two adjacent slits, i.e. the grating constant, of a diffraction grating with n lines per millimetre.
7. To measure the wavelength of light with a diffraction grating:
   
   where n is the order of the image,  is the wavelength of the light, d is the grating constant and  is the angle between the n^th  image and the central image.