IES MACARENA
PHYSICS AND CHEMISTRY 2o ESO – UNIT 9
UNIT 9 - WAVES I: BASIC CONCEPTS
1. WHAT IS A WAVE?
A wave is an oscillation that spreads across space, carrying energy but no matter.
Oscillation can be in air pressure, along a string, in water, etc.
There are two different movements: the oscillation (of the string, for example) and the
propagation of the wave.

Activity 1 Using the example of a wave in a string explain what is the difference between
propagation and oscillation. [Go to Educaplus-Física-Ondas-Ondas longitudinales y
transversales, and pay attention to the red points].
2. CHARACTERISTICS OF A WAVE
Waves are described using several physical quantities:
Wavelength (λ) is the distance between two points with the same state of oscillation. It can also
be defined as the distance between two consecutive peaks (crests) or two consecutive troughs.
Its unit is meter (m).
Frequency (𝝂) is the number of oscillations that a wave produces in one second. Its unit is hertz
(Hz).
Period (T) is the time that a wave takes to make an oscillation. Its unit in the Si is second (s).
Amplitude (A) is the maximum distance (from the point of rest) that an oscillation can reach. It
can be defined as the maximum height of a peak or the maximum depth of a trough.
Speed of propagation (v) of a wave is the speed with which the wave travels. It can be calculated
by multiplying its wavelength and its frequency:
v = λ·𝝂
- Activity 2 Find out the speed of sound from this data:
o wavelength λ = 34 cm
o frequency 𝝂 = 1000 Hz
3. TYPES OF WAVES
FIRST CLASSIFICATION: Waves can be classified according to their capacity for traveling in a
vacuum:
A - Mechanical waves can’t travel through a vacuum. These waves need some material to travel
through. For example: water waves, waves in a string, seismic waves and sound.
B - Electromagnetic waves can travel through a vacuum. They all travel at 300,000 km/s. All the
electromagnetic waves are represented in the electromagnetic spectrum:
-
Gamma rays.
X-rays
Ultraviolet light.
Visible light. (or just “light”)
Infrared light
Microwaves.
Radio and TV waves.
SECOND CLASSIFICATION: Waves can be also classified according to the direction of their
oscillation:
Longitudinal waves: oscillation and propagation have the same direction. Examples of
longitudinal waves are: waves in a spring and sound.
Transverse waves: oscillation and propagation have perpendicular directions. Examples of
transverse waves are: waves in a string and light.
In this picture you can see that:
- Oscillation and propagation are horizontal in the spring
- Oscillation is vertical and propagation is horizontal in the string