WAVES

WAVES AND ENERGY

Waves and Energy

Wave – a traveling disturbance that carries energy from one place to another

Waves do not carry matter; waves carry energy

Vibration – movement that follows the same path over and over again

Wave – movement of energy from a vibrating source outward

Medium

The matter or substance through which a wave is transmitted

Ex. Water – medium for ocean waves

Air – medium for sound

MECHANICAL WAVES

waves that require a medium

Ex. Sound and water waves

ELECTROMAGNETIC WAVE

Wave that consists of electric and magnetic fields

Do not require a medium

Ex. Light, microwaves, x-rays

CHARACTERISTICS OF WAVES

Amplitude

Wavelength

Frequency

Amplitude

Greatest distance from normal resting position to top (crest) of the wave

Indicates the amount of energy carried by the wave

Wavelength

Distance between two crests or two troughs (lowest point)

Usually measured in meters or centimeters

Symbol for wavelength is lambda λ

Frequency

Frequency – the number of complete waves or complete cycles per unit time

Unit: Hertz (Hz) = 1 wave/second

TYPES OF WAVES

Transverse waves

Longitudinal Waves

AKA compressional wave

TRANSVERSE WAVES

A wave in which the motion of the medium is at right angles to the direction of the wave

Movement of particles is up and down – vertical

Movement of the wave is horizontal

Ex Waves on a rope, water waves, light, electromagnetic waves

LONGITUDINAL WAVES

AKA compressional wave

Wave in which the motion of the medium is parallel to the direction of the wave

A series of compressions and rarefactions

Rarefaction – space in the medium in which there are fewer particles

Ex Sound waves

SPEED OF WAVES

Speed = frequency x wavelength Speed of a wave is constant

within the same given medium If frequency is increased then

wavelength must decrease for constant speed to be maintained

The speed of a wave depends upon the medium

The density of the medium affects the speed of mechanical waveso The more dense a medium , the

slower light waves travel but the faster sound waves travel.

Elasticity of the medium affects the speed of waves

Elasticity – ability of a medium to return quickly to its original shape after being disturbed

The more elastic – the faster the wave

WAVE INTERACTIONS

Reflection

Refraction

Diffraction

Interference

Standing waves

Resonance

REFLECTION

Bouncing back of waves upon reaching another surface

Echo

Mirror image

LAW OF REFLECTION

The angle of incidence (i) is equal to the angle of reflection (r)

Ray – line drawn in the direction of motion of a wave Incidental ray – incoming ray (incoming

wave)

Reflected ray – ray (wave) that bounces off barrier

Angle of incidence (i) – angle formed by the incident ray and the normal

Angle of reflection (r)- angle formed by the reflected ray and the normal

Normal – line drawn perpendicular to barrier

Refraction

The speed of a wave changes as the wave travels from one medium to another

Refraction – the bending of waves due to a change in speed

Refraction occurs because waves move at different speeds in different mediums

If wave slows down it is bent to the normal

If it speeds up, it is bent away from the normal

DIFFRACTION

The bending of waves around the edge of an obstacle or through a narrow opening

INTERFERENCE

Interaction of waves that occur at the same place at the same time; the wave combine to make a single wave

Constructive interference – crest meets crest; the amplitudes add together creating a larger amplitude

Destructive interference – crest meets trough; the amplitudes subtract from one another creating a smaller amplitude

EXAMPLE OF DESTRUCTIVE INTERFERENCE

STANDING WAVES

Wave that does not appear to be moving; occurs at the natural frequency of the material

Nodes – points at which destructive interference results in no energy displacement

Antinodes – points at which constructive interference causes maximum energy displacement

Resonance frequency – frequency at which a standing wave occurs

RESONANCE

The ability of an object to vibrate by absorbing energy at its natural frequency

Video

Video 2

POLARIZATION

Alignment of vibrations in a transverse wave

Usually by filtering out waves of other directions

Polarizing filters – transmit only light waves that vibrate in the same plane

Polarized sun glasses Reduce glare