TYPES OF MECHANICAL WAVES
1. TRANSVERSE WAVE:-
In this wave, the particles of the medium vibrate about their mean position at the right angle to the direction of propagation of the waves.
Ex- wave on a string, Waves on the surface of the water. etc
LONGITUDINAL WAVE
In this wave, the particles of the medium move back and forth about their mean position along the direction of propagation of the wave.
Ex- sound wave, wave on string etc
NOTE
1. A transverse wave is formed of crests and troughs. But the longitudinal wave is formed of a series of compression and rarefaction.
2. Transverse waves can propagate only in solid. But longitudinal waves can propagate in all types of medium (solid, liquid and gas).
Transverse waves are possible only when each element of the medium is subject to shearing stress. Solid, string etc have shear modulus i.e they sustain shearing stress. This is why transverse waves are possible in solid and string (under tension) but not in the fluid.
Solid as well as fluid have bulk modulus, i.e they can sustain compressive strain. Since longitudinal waves involve compressive stress (pressure), they can be propagated through solids and fluids.
In other words, we can say that transverse waves require a relatively rigid medium in order to transmit their energy. As one particle being to move it must be able to exert a pull on its nearest neighbour. If the medium is not rigid as is the case with fluids, the particles will slide past each other.
3. In a transverse wave, there is no pressure variation but in longitudinal waves pressure and densities are varied.
4. While waves that travel within the depths of the ocean are longitudinal waves, the waves that travel along the surface of the oceans are referred to as surface waves. A surface wave is a wave in which particles of the medium undergo a circular motion. Surface waves are neither longitudinal nor transverse. The radius of the circles decreases as the depth of the water increases. In surface waves gravity and surface tension acts as a restoring force.
5. When a solid propagates longitudinal and transverse waves, its speeds can be different since they arise from different elastic moduli.
NOTE
We can look at a wave in two ways. We can fix an instant of time and picture the wave in space. This will give us the shape of the wave in space at a given instant. Another way is to fix a location i.e fix our attention on the particular element of string (wave) and see its oscillatory motion in time.
| Q.1 Given below are some examples of wave motion. State in each case if the wave motion is transverse, longitudinal or a combination of both: (a) Motion of a kink in a longitudinal spring produced by displacing one end of the spring sideways. (b) Waves produced in a cylinder containing a liquid by moving its piston back and forth. (c) Waves produced by a motorboat sailing in water. (d) Ultrasonic waves in air produced by a vibrating quartz crystal. |
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