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Background

The term wave is used mainly to refer to water waves or an event taking place on a large scale, like in a political activity. In Physics, however, waves are associated with the transfer of energy within a medium. In this topic, we are going to learn types of waves and some of their effects.









Specific objectives

By the end of the topic, you should be able to:

  • Describe the formation of pulses and waves
  • Describe Transverse and Longitudinal waves
  • Define amplitude(A), Wavelength (l) frequency (f) and Periodic time T)
  • Derive the relation v = fl
  • Solve problems involving v = f l

 





Introduction

Our physical environment experiences a lot of phenomena arising from wave energy. Examples include earth tremors, mortar explosions, radio and television satellite communications and ocean waves, among others. In this topic, we are going to learn about the general properties of waves.


Formation of pulses and waves

Pulse

What comes to your mind when you hear the term pulse? Play the animation and observe the action of a pumping heart and a tuned loudspeaker (This follows shortly after the heart beats).

Observations: The heart is observed to beat regularly or rhythmically. The tuned loudspeaker cone surges back and forth at regular intervals. Each of these movements is called a pulse. A pulse is a burst of wave energy caused by a disturbance on a medium. Pulses can also be produced by disturbances in a rope, slinky spring and other vibrating objects.

Wave

Play the video clip, which involves disturbances in a slinky spring, and make observations.



What you have observed is a series of pulses following one another?These pulses constitute a wave.

Longitudinal and transverse waves

In the video clip below, observe the effect of disturbing a slinky spring along its axis in and out. Wait to view the second portion of the clip, in which the disturbances are perpendicular to the spring. What is the main difference between the two waves produced?


(a) Longitudinal waves
This is whereby the vibrations are in the same direction as the direction of tavel of the wave. Examples of such waves include waves travelling along the axis of a slinky spring and sound waves.

To demonstrate longitudinal waves: Longitudinal waves from a tuning fork. click on the tuning fork and observe what happens.


(b) Transverse waves
When the disturbances are perpendicular to the slinky spring, peaks and troughs are observed as the wave travels from one end to another. That is, the vibrations are at right angles to the direction of travel of the wave. Such waves are called transverse waves. Examples of transverse waves include water waves, light waves and radiowaves.


 

Definition of terms

The following are the terminologies used in description of waves:

  • Amplitude (A)
  • Wavelength(l)
  • Frequency (f)
  • Periodic time (T)
  • Velocity (v)

These terms are explained with the aid of animations presented in the next section.

 

Wavelength

The animation below represents a wave (not particle) moving from point O to P, P to Q and Q to R. How far does the wave move during one cycle?

The distance OP is covered during one cycle of the wave; so it is called wavelength.

A wavelength is the distance covered by a wave during one complete oscillation or one cycle. Wavelength is conventionally represented by the Greek letter,l called lambda.

Frequency (f)

This is the number of complete oscillations made by a wave in one second. It is measured in Hertz (1Hz means 1 cycle per second).

ANIMATION: Copy and paste the same animation with the horizontal axis representing time and three complete oscillations be done in one second. A voice over with the words “three oscillations in one second hence three Hertz

Periodic time (T)

This is the time taken by a wave to make one complete oscillation.

Wave equation (v = fl)

The wave terminologies already discussed, that is, wavelength, frequency and periodic time can be combined into one equation known as the wave equation.

To derive this equation, consider a wave moving from point O to point P in a time of T seconds.

We define velocity of the wave as its displacement, per second. A displacement of one wavelength, l, is covered in one periodic time, T,from definition.


 

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