Waves

Waves

What is a wave? • A wave is a rhythmic disturbance that transfers energy. • When a wave moves through matter, the matter moves back and forth but moves back to the original position.

Examples of Waves • Slinky waves - A slinky illustrates a mechanical disturbance caused by a force moving one of the spring coils. • The energy of a wave in a slinky will pass from one end to the other.

Sound Waves • A sound wave is a mechanical disturbance caused by a force moving molecules in the medium through which it passes. • A sound wave travels out in all directions from a vibrating object • A sound wave travels through the medium

Light Waves • A light wave is energy that can be transmitted without mechanical disturbance of the particles of a medium • Light waves travel in straight lines in all directions from the light source • Light waves do not need a medium to travel through

Types of Waves • Electromagnetic waves may travel through a medium but do not need a medium for transmission • Mechanical waves must have a medium through which to move. – Mechanical waves transfer energy through the particles of a medium

Types of Mechanical Waves • Transverse waves - the waves moves through the medium in a direction that is perpendicular (up and down) • Ex: waves in guitar, secondary earthquake waves

Types of Mechanical Waves • Longitudinal/compressional - the wave moves through the medium in a direction that is straight across • Ex: Sound, primary earthquake waves

More Vocabulary • In a transverse wave the point of maximum displacement of the particles in a medium from the equilibrium is called a crest or trough • In a longitudinal wave the particles of the medium are pushed together to form a high pressure area called a compression and spread out to form a lower pressure area called a rarefaction

Parts of a Waves Wavelength (λ) • The length of one wave • The distance between two crests • Measured in meters

Parts of a Wave (cont)

Frequency Frequency (f) •The number of waves that pass by in a second •Measured in Hertz (Hz) •1 Hz = 1 1/s • If you increase the Frequency of a wave, the wavelength gets shorter

Amplitude Amplitude • The height or strength of a wave • The greater the energy of the wave, the greater the amplitude

Period • The period of a wave is the time for one cycle or the time for one complete wave to pass • The period is measured in seconds • The period and the frequency are inversely related. An increase in frequency would result in a decrease in period.

Speed of a Wave Speed (v) Units = m/s

v = λf

Wavelength (λ) Units = m

Other formulas to know that you will not be given on the test:

Frequency (f) Units = Hz (1/s )

f = v/λ

λ= v/f

Example Problems What is the speed of a wave with a wavelength of 1.3 m and a frequency of 60 Hz? v = λf v = (1.3 m)(60 Hz) v = 78 m/s What is the speed of a wave with a wavelength of 4.10 m and a frequency of 50.0 Hz? v = λf v = (4.1 m)(50 Hz) v = 205 m/s

Example Problems What is the frequency of a wave with a wavelength of 2.0 m and a speed of 80 m/s? f = v/λ f = (80 m/s)(2 m) f = 40 Hz What is the frequency of a wave with a wavelength of 6.0 m and a speed of 90 m/s? f = v/λ f = (90 m/s)(6 m) f = 15 Hz

Example Problems What is the wavelength of a wave with a speed of 20 m/s and a frequency of 5.0 Hz? λ = v/f λ = (20 m/s)/(5 Hz) λ = 4.0 m What is the wavelength of a wave with a speed of 36 m/s and a frequency of 4.0 Hz? λ = v/f λ = (36 m/s)/(4 Hz) λ = 9.0 m