Waves
What is a wave? A wave is a repeating movement or disturbance that transfers energy through matter or space. Medium is the matter through which a wave travels. A medium can be solid, liquid or gas. Not all waves need a medium to travel through- light and radio waves can travel through space. There are two types of waves: mechanical waves and electromagnetic waves.
Mechanical Waves Mechanical waves are waves that can only travel through a medium. Examples of this type of wave are sound waves and water waves. Transverse Waves - Matter moves back and forth at right angles to direction that the wave travels Longitudinal Waves - Matter in a medium moves in the same direction that wave travels.
Electromagnetic Waves Electromagnetic waves are made by vibrating electrical charges and can travel through space. The electromagnetic spectrum is the entire range of electromagnetic wave frequencies. It includes: radio waves, infrared waves, visible light, ultraviolet waves, x-rays, and gamma rays.
Parts of a Wave Crests- the highest points on a wave Trough- the lowest points of a wave Wavelength- the distance between waves, from crest to crest or from trough to trough. Amplitude is the height of a wave from normal position to crest or trough
Parts of a Wave Longitudinal waves have dense regions (coils close together) called compressions and less dense regions called rarefactions.
Behavior of Waves Reflection occurs when a wave strikes an object and bounces off of it- all types of waves can be reflected (ex. sound, water, and light). Refraction is the bending of a wave caused by a change in its speed as it moves from one medium to another. (Exm. pencil in water) Diffraction in an object causes a wave to change direction and bend toward it. Interference is when two or more waves overlap and combine to form a new wave.
Amplitude vs Frequency
Amplitude- a measure of energy in a wave (decibels- dB) The more energy a wave carries the greater the amplitude. Amplitude is also known as the volume of a wave. As wave height increases, volume increases Frequency the is the number of wavelengths that pass a fixed point each second (hertz- Hz) - Frequency is also known as pitch. As wavelength increases, pitch decreases
Amplitude versus Frequency Which one will have the higher pitch? (circle it) Amplitude Which one will have the higher volume? (circle it)
What can you hear? Hertz (Hz): Pitch Decibels (dB): Volume Normal Speech: 60dB Library: 40dB Close Whisper: 20dB Jet Engine: 140dB Loud Rock Music: 110dB Subway Train: 100dB Busy Street Traffic: 70dB 120dB or above usually causes pain to the ear Hertz (Hz): Pitch Young people can hear frequencies between 20-20,000 Hz Dogs can hear frequencies that range from 67-45,000 Hz As you age, your ability to hear high frequency sound decreases.
Speed of a Wave
Thunderstorms During a thunderstorm, you usually see the flash of lightning first followed by the roll of thunder. Both occur at the same instance, but they reach you seconds apart. Sound and light travel at very different speeds, light travels faster than sound.
Speed of a Wave Speed of a wave is calculated by multiplying the frequency and the wavelength. (Speed= frequency x wavelength) Waves in different mediums travel at different speeds.
(Formula: Speed= Frequency x Wavelength) Sample Problem The frequency of a rope wave is 5 Hz and its wavelength is 10cm. What is the speed? (Formula: Speed= Frequency x Wavelength) Frequency= Wavelength=