Comprehensive Question 5: How waves transport energy without carrying the material medium? Also describe the connection between oscillatory motion and wave.
Answer
WAVES TRANSPORT ENERGY WITHOUT CARRYING THE MATERIAL MEDIUM
Waves transfer energy from one place to another without the actual movement of the particles. The particles of the medium oscillate about an equilibrium position. The particle transfers the oscillation to the adjacent particles due to intermolecular forces and the wave moves onward. Thus the energy is transferred to the next particle as its K.E, and as the wave passes on, the original particle comes to rest.
Consider a tub full of water. Move a pencil up and down at one side of the tub. Now place a piece of paper in the middle of the tub. As you move the pencil, note that;
- As you move the pencil up and down, transverse waves are produced on the surface of water. When the wave reaches the paper, it starts oscillating up and down about its own place.
Thus the energy spent on moving the pencil up and down has reached the paper by the waves in the water and the paper is now oscillating.
- Similarly, the paper does not go with the wave but just move to and fro. This means the particle of water does not move with wave and just executes oscillatory motion about their mean positions.
These two conclusions show that waves transport energy without carrying the material particles.
CONNECTION BETWEEN OSCILLATORY MOTION AND WAVE
Wave motion and oscillation are related phenomena. As the wave moves onward through the medium, the particles of the medium execute simple harmonic motion about their equilibrium positions. The onward motion of the wave is due to the oscillatory motion of the particles of the medium and the oscillatory motion of the particles is due to the motion of the wave.
Example
Take a rope and color a point on it. Attach one end of the rope to a wall and shake the other end of the rope periodically up and down. A number of waves will be produced in the rope moving towards the fixed end of the rope. Observe the colored point, it executes oscillation about a certain mean position. Thus the motion of the wave and the oscillatory motion of the particles of the rope are connected.