Question

The change of frequency experienced by the receiver either because of the relative motion of the source or receiver or both:

• A. Joules law
• B. Ohm's law
• C. Doppler effect
• D. Fleming's left hand rule

Answer 1

Answer:

C. Doppler effect

• When a source and detector of sound separated by a large distance are at rest relative to
  the medium (usually air) the detector (usually listener) receives the same number of
  waves per sec as that emitted by the source. However, if there is motion of source and/or
  detector relative to the medium along the line of sight, the number of waves received per
  sec is usually different from that emitted and the frequency or pitch of the source appears
  to be different. This apparent change in frequency or pitch due to motion of source and
  detector relative to the medium along the line of sight is called Doppler Effect
  Let us consider the case when both source and detector are moving along the same line
  with detector ahead, with speeds vs and vo respectively relative to the medium air, at rest