Question

If one puts one ear to the steel rail, the sound of a coming train can be heard even when the train cannot be seen. One can conclude from this observation that:
(A) Sound travels faster in steel than in air
(B) Amplitude of sound in the rail is much larger than in air
(C) Sound can travel larger distance in solids than in air
(D) Quality of sound in rail is better than in air
(A) A and C
(B) A and B
(C) B and C
(D) None of these

Answer 1

In order to answer this question, we need to know the characteristics of sound in different mediums. We know sound travels faster in closely packed mediums compared to the medium in which the molecules are loosely placed. When the speed of the sound increases, it covers greater distances.

Complete Step-By-Step Solution:
In the case of solid mediums, we know that molecules are very closely placed, such that they are in contact with each other. On the other hand, in case of gaseous medium the molecules are placed far away from each other.
Therefore, in case of a steel rail the molecules are very closely placed thus, when vibration of sound wave starts, the molecules placed close to each other collide at a faster rate, and this enables sound wave travel at a greater speed. Thus in case of steel rail, the sound travels faster.
Whereas, in case of air, molecules being placed far away from each other, causes delay in collision, therefore, sound travels at a lower speed.
Thus we can say sound travels faster in solids than in air.
On the other hand, since the speed of sound in solids are more, therefore, speed being directly proportional to distance, the distance travelled by sound is high when speed is high.
In case of air, the speed of sound being low in comparison to that of solid, the distance travelled by it is also less.
Therefore, we can say distance travelled by sound in solids in more than distance travelled in air.

Thus, option (A) is correct.

Note:
Speed with which sound travels only depends upon the medium through which it propagates. Therefore, the amplitude of the wave doesn’t affect its speed. Thus, two waves having the same speed can have different amplitudes, or vice-versa.