Waves What are waves?

Wave Definition: A disturbance that transfers energy from place to place. What carries waves? A medium, a medium is the material through which a wave travels. A medium can be a gas, liquid, or solid.

Not all waves require a medium to travel. Light from the sun travels through empty space.

What causes waves? Waves are created when a source of energy causes a medium to vibrate. A vibration is a repeated back and forth or up and down motion.

Types of waves: Waves are classified according to how they move.

Transverse wave Waves that move the medium at right angles to the direction in which the waves are traveling is called a transverse wave. Transverse means across.The highest parts are called crests the lowest parts are called troughs.

Compressional Wave Matter vibrates in the same direction as the wave travels. Example: Slinky

Compressional wave The parts,where the coils are close together are called compressions, the parts where the coils are spread out are called rarefactions.

Combinations of waves Surface waves are a combination of transverse and longitudinal waves.The waves occur at the surface between water and air.

Wave Properties

Basic Properties of Waves Amplitude Wavelength Frequency Speed

Draw a transverse wave: Label crest & trough

Draw a compressional wave: Label compression & rarefaction

Amplitude Amplitude is the maximum distance the particles of the medium carrying the wave move away from their rest positions. The farther the medium moves as it vibrates the larger the amplitude of the resulting waves. The greater the amplitude the greater the amount of energy

Amplitude of transverse waves You can find the amplitude of a transverse wave by measuring the distance from rest to crest or rest to trough.

Amplitude of a longitudinal wave. The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes.

Wavelength A wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is its wavelength. Transverse measure from crest to crest or trough to trough. Longitudinal measure from one compression to the next.

Frequency The number of complete waves that pass a given point in a certain amount of time. AKA number of vibrations per second. Frequency measured in hertz (Hz).

Period The period of a wave is the amount of time it takes one wavelength to pass a point. As the frequency of a wave increases, the period decreases. Period has units of seconds.

Comparing frequency and period The frequency is the number of waves that pass through a point in one second. *Measured in Hz The period of a wave is the time it takes for 1 wave to complete it’s cycle. *Measured in seconds

Speed Where, v is the speed of the wave (m/s) The speed, wavelength, and frequency of a wave are related to each other by a mathematical formula. Where, v is the speed of the wave (m/s) λ is the wavelength in meters (m) f is the frequency in Hertz (cycle/s)

Speed Waves in different mediums travel at different speeds. However, in a given medium and under the same conditions the speed of the wave is constant.

The Behavior of Waves

Ways Waves Interact Reflection Refraction Diffraction Interference Constructive Destructive Standing Waves

Reflection When an object or wave hits a surface through which it cannot pass, it bounces back. Angle of incidence Angle of reflection

Examples of reflection Mirror Echo Ball against a wall

The Law of Reflection According to the law of reflection, the angle of incidence is equal to the angle of reflection. All reflected waves obey this law.

Refraction Refraction is when a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium which causes it to bend. The bending of waves due to a change in speed is called refraction.

Though all waves change speed when they enter a new medium Though all waves change speed when they enter a new medium. Bending occurs when one side of the wave enters the new medium before the other side

Refraction of Light in Water Light waves travel slower in water than in air. This causes light waves to change direction when they move from water to air or air to water. When light waves travel from air to water, they slow down and bend toward the normal.

In the figure, the light waves reflected from the swimmer’s foot are refracted away from the normal and enter your eyes. However, your brain assumes that all light waves have traveled in a straight line.

Diffraction When waves strike an object, several things can happen. The waves can bounce off, or be reflected. If the object is transparent, light waves can be refracted as they pass through it. Waves also can behave another way when they strike an object. The waves can bend around the object.

Diffraction occurs when an object causes a wave to change direction and bend around it. Diffraction and refraction both cause waves to bend. The difference is that refraction occurs when waves pass through an object, while diffraction occurs when waves pass around an object.

Interference Constructive interference occurs whenever two waves combine to make a wave with a larger amplitude. Destructive interference when the amplitudes of two waves combine producing a smaller amplitude.

Standing waves: If the incoming wave and the reflected wave combine at the right places the combined wave appears to be standing still. It appears to be standing in one place, even though it is two waves interfering as they pass through each other.

Nodes and Antinodes Nodes: at certain points, destructive interference causes the two waves to combine and produce an amplitude of zero. Antinodes are the points of maximum energy. The crests and troughs of a standing wave.

Resonance Most objects have a natural frequency of vibration. Resonance occurs when vibrations traveling through an object match the object’s natural frequency. An object that is vibrating at its natural frequency absorbs energy from the objects that vibrate at the same frequency. Occurs in music.