Optics Answers

 Give an example of change in frequency due to motion of source or observer from some other

      branch of physics, explaining either a use which is made of it, or a deduction from it.

Deduce expressions for the frequency heard by an observer

(a.) when he is stationary and a source of sound is moving towards him and

(b.) when he is moving towards a stationary source of sound.

      Explain your reasoning carefully in each case.

 A train, sounding its whistle, is travelling along a long section of track and passes under a low bridge.

     Explain how the frequency of the note heard by an observer standing on the bridge differs from the

     frequency emitted. 

  Compare the shift in frequency if a 2000Hz source is moving towards you at 15ms-1 versus if you are moving towards it at 15ms-1. Are the two frequencies exactly the same? Are they close? Repeat

the calculation for 150ms-1 and then again for 300ms-1. What can you conclude about the asymmetry of the Doppler formulas? Show that at low speeds (relative to the speed of sound), the two formulas-source approaching and detector approaching-yield the same result.

   Two automobiles are equipped with the same single-frequency horn. When one is at rest and the

      other is moving toward an observer at 15ms^-1, a beat frequency of 5.5Hz is heard. What is the

      frequency the horns emit? Assume T = 20°C.

  In one of the original Doppler experiments, one tuba was played in a moving platform car at a

      frequency of 75Hz, and a second identical one was played on the same tone while at rest in the railway station. What beat frequency was heard if the train approached the station at a speed of

      10.0ms^-1?

An ambulance travels down a highway at 120kmh^-1, its siren emitting sound of frequency 400Hz. What is the frequency heard by a passenger in a car traveling at 90kmh^-1 as the car approaches and

by-passes the ambulance? 

  (i.) What is meant by Doppler's effect?

  (ii.) A bat flies at a steady speed of 5ms^-1 and emits waves of frequency 85.0kHz. What is the

       frequency of the wave detected by the bat after reflection from a stationary obstacle directly ahead of the bat?

A stationary observer hears beats when a source of sound of frequency 100Hz moves directly away from the observer with a speed of 10.0ms^-1 towards a vertical wall. Explain why beats are produced and calculate the beat frequency

State the principle of superposition of waves. 

How is this principle observed in the formation of maxima and minima of a typical diffraction pattern