Wave

What is wave?
Many earthquakes happen in places such as Indonesia. How? It is caused by the vibration that is deep inside the Earth, which leads to shaking the surface. This vibration does not happen only where the original place of the earthquake is which are deep inside the Earth, but it spreads, creating waves that eventually reaches the surface and shaking it. Seismic waves are not the only waves that exist, but sunlight, sound and cell-phone signal uses waves also to move to other places.

Elements of wave
Similar to the vibration section of physics, waves also have terms and conventions. Those are transverse waves and longitudinal waves
Transverse wave
Transverse waves happen on a rope or
on water. Transverse waves are always in a form of a peak and a valley of the wave. The height of the peak and the valley is considered as the amplitude of the wave. A complete wave is always consists of one peak and one valley of the wave. A complete wave is called a wave-length.






Longitudinal Waves
Longitudinal waves are waves that have a compression part and a expansion part, instead of a peak or valley. A complete wave of a longitudinal wave consists of one compression part and one expansion part. The length of a longitudinal wave is equal to the length of a wave that consists of a compression part and a expansion part.


Examples

1 complete wave = a - b - c - d - e
It consists one peak (a) and one valley (c)

A to B= 1/4 wave
A to C= 1/2 wave
A to D= 3/4 wave
A to E= 1 full wave

A to F = a - b - c - d - e - f = 1 1/4 waves
A to H = a - b - c - d - e - f- g - h = 1 3/4 waves

Chapter 18 Exercise

No 1. Look at the following figure of a pendulum. A motion of 2 vibrations is                   shown as the following successive motion......

           Answer: 1-2-3-2-1-2-3-2-1




No 3.Look at the following figure of a spring. If the spring moves as a-b-c-b-a-b-c-b-a, its motion performs . . . .
Answer: 2 full vibrations






No 5. If 120 vibrations happen in 30 seconds, the correct statement  is . . . .
Answer: The period of the vibration is 1/4 seconds
             P= T÷N
           =30÷120
           =1/4

No 6. A period of a swing is 20 seconds. In every minute, the pendulum will perform........
Answer: 60÷20= 3 swings

No 7. Look at the figure of a ruler that is placed on a table. If in 1/4 seconds the ruler moves in the b-c-b-a-b-c-b pattern, period of the vibration made by the ruler is . . . .

Answer:P=t÷n
            P= 1/4 ÷ 1 1/2 or 3/2
            P= 1/4 x 2/3
            P= 2/12= 1/6 seconds

No 9.  A pendulum performs swings with a frequency of 10 Hz. The number of vibrations that it can make within 5 minutes is . . . .
Answer: 10Hz= 10 vibrations in one second
             = 10 x 300 seconds (from the 5 minutes)
             = 3000 vibrations