**Useful Equations**

__Relationship between frequency and wavelength__:

Wavelength(in cm) = c /
Frequency(in Hz)

Frequency (in Hz) = c / Wavelength (in cm)

where c = 3 × 10^{18 }cm/s

__Doppler Equation:__

Observed frequency = Emitted frequency × (1 -
Velocity/c)

Velocity =c × (1 - Observed frequency / Emitted
frequency)

Note: Velocity is > 0 if object is moving away from us; .Velocity is
< 0 if object is moving toward us