Evan's Space

Wonders of Physics

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Time interval between two sounds from a gun – direct and reflected sound


Solutions: Option B

You can view the video tutorial here or the written solutions below.

time interval between 2 sounds ans


Demonstration of Reflection, Refraction and TIR using light source with a slit

Reflection of light using a mirror

Refraction of light using various shaped optical mediums

Total Internal Reflection (TIR) using a semi-circular perspex

For Total Internal Reflection (TIR) to occur:
1) angle of incidence i is greater than the critical angle c
2) the light is travelling from a denser medium towards a less dense medium

Click on this post for the explanation of TIR


N2005P1Q24 Sound – Reflection of sound from 2 walls

A man who is standing at a point X between two parallel walls (as shown in the diagram) fires a starting pistol.


He hears the first echo after 0.6s and another one after 0.8s. How long after firing the pistol will he hear the next echo?


View video tutorial to visualise the distance travelled.

Time taken to hear next echo = 0.6 + 0.8 = 1.4s

The distance travelled by sound (left and right) from X is the same during 3rd and 4th echos.

Hence 3rd and 4th echos actually coincide. And time taken is 0.6 + 0.8 = 1.4s.