## Introduction to waves

Introduction to waves:

A wave is a transfer of energy between two points without any transfer of matter.

Mechanical: waves transferred through a material by particle vibration. For example, sound waves and primary seismic waves.

Electromagnetic: waves transferred by the concurrent oscillations of electric and magnetic fields. For example, light waves, radio waves, X-rays… etc.

Longitudinal: An oscillation where the displacement of particles from the mean position is parallel to the direction of energy propagation. For example, sound waves and p-seismic waves.

Transverse: An oscillation where the displacement of particles from the mean position is perpendicular to the direction of energy propagation. For example, all EM waves and secondary seismic waves.

Key Terms:

• Wavelength (Represented by  the Greek symbol, Lambda, λ): The distance between a point on one wave and the identical point on the next wave. I.e. Crest to crest or trough to trough. This can be linked with wave speed and frequency by the equation, v (velocity/wave speed) = λ (wavelength) x f (frequency)
• Displacement: The displacement of a vibrating particle is the distance and direction from its equilibrium position, i.e the particle’s displacement from its mean position.
• Amplitude, a: The amplitude of a wave is the maximum displacement of a vibrating particle. For a transverse wave, this is the height of a wave crest or the depth of a wave trough from its mean (equilibrium) position.
• Period, T: The time for one complete wave to pass a fixed point. The period of a wave is equal to 1/f (frequency).
• Frequency, f: This is the number of waves which pass a fixed point in one second. The unit is Hertz (Hz).

Using the wavelength equation:

Example:

QUESTION- What is the frequency of orange light with a wavelength of 600 nm?

ANSWER- Use the equation v= λf, rearrange it to get f= v/λ to find the frequency.

Since you are finding the frequency of a light wave, you must know the speed of light, 3×10⁸.

Substitute in your values: f= 3×10⁸/ 600= 500,000

You can put this value into standard form.