Question Answers

Wave Motion

1. How is energy transmitted in wave motion?

The neighboring oscillating parts of the medium are coupled together through elastic forces or intermolecular forces. During wave motion, a part of the medium is set into oscillation. This part hands over its motion to the next part of the medium due to the forces and so on. This results in transmission of energy.

2. Is an oscillation a wave? Give a reason.

No, an oscillation is not a wave. The term wave implies the transfer of energy through successive vibrations of the particles of the medium. Hence the oscillations of the body do not constitute a wave.

3. What is meant by a non-dispersive medium?

A medium in which speed of a wave is independent of frequency of wave is called a non-dispersive medium. For example, air is a non-dispersive medium for sound waves.

4. When a stone is thrown on the surface of water, a wave travel out. Where does the energy come from?

As the stone hit the surface of water, it losses most of its KE as it slows down. This KE is then carried by waves in water. Thus, energy in these waves come from the KE of falling stone.

5. What causes the rolling sound of thunder?

The rolling sound of thunder is caused by the multiple reflections of the sound of lightning between the clouds and the earth's surface.

6. Frequency is the most fundamental property of a wave. Why?

The frequency of a wave remains the same when it travels from one medium to another medium because it is determined by the wave source. The velocity of the wave changes with medium and Wavelength is dependent on velocity of propagation within the medium where it is passing by. Hence, frequency is the most fundamental property of a wave.

7. How are stationary waves formed

When two progressive waves of same amplitude and same frequency travelling in opposite direction along the same straight line superimpose on each other, the resulting wave formed is stationary wave. The disturbance of the wave is localized between nodes. At nodes the particles are at rest and at antinodes the particles oscillates with maximum amplitude.

8. If you are walking on the moon surface, can you hear the cracking sound behind you? Explain.

No, we cannot hear the cracking sound during walking on the moon surface. It is because there is no atmosphere on the moon. Hence sound waves cannot propagate as there is no medium. Thus, we cannot hear sound on the moon surface.