Waves, Sounds, and Light

A wave is a disturbance that transmits energy.

The particles of a medium do not travel with the wave.

Mechanical waves require a medium, but electromagnetic waves do not

Particles in a transverse wave vibrate perpendicularly to the direction the wave travels. Link

Particles in a longitudinal wave vibrate parallel to the direction that the wave travels.

Wave Properties

• Amplitude is the maximum distance the particles of a medium vibrate from their rest position.

• Wavelength is the distance between two adjacent corresponding parts of a wave.

• Frequency is the number of waves that pass a given point in a given amount of time.

• Wave speed can be calculated by multiplying the wave’s wavelength by the frequency.

Wavelength

The shorter the wave, the higher the

energy!

Frequency

The higher the frequency, the

higher the energy!

Wave Modeling Spring

• How do transverse & compression waves compare?

• How do they contrast?

• What effect does increasing the energy into the wave have?

• What relationship do you see between wave frequency and wavelength?

• Waves on a String PhET

Wave Interactions

• Waves reflect after hitting a barrier.• Refraction is the bending of a wave when it passes

through different media.• Waves bend around barriers or through openings

during diffraction.• The result of two or more waves overlapping is called

interference.• Amplitude increases during constructive interference

and decreases during destructive interference.• Resonance occurs when a vibrating object causes

another object to vibrate at one of its resonant frequencies.

Reflection: Waves reflect after hitting a barrier.

Refraction: The bending of a wave when it passes through different media.

Diffraction: Waves bend around barriers or through openings

The result of two or more waves overlapping is called interference.

Amplitude increases during constructive interference and decreases during

destructive interference.

Constructive & Destructive Interference

• PhET simulation

• Demonstration

Resonance

• Resonance occurs when a vibrating object causes another object to vibrate at one of its resonant frequencies.

• Tacoma Narrows Bridge

• Wine Glass

Practice

• Which of the following results in more energy in a wave?

• A. a smaller wavelength

• B. a lower frequency

• C. a shallower amplitude

• D. a lower speed

Answer

• Which of the following results in more energy in a wave?

• A. a smaller wavelength

• B. a lower frequency

• C. a shallower amplitude

• D. a lower speed

Practice

• Refraction occurs when a wave enters a new medium at an angle because

• A. the frequency changes.

• B. the amplitude changes.

• C. the wave speed changes.

• D. the new medium changes.

Answer

• Refraction occurs when a wave enters a new medium at an angle because

• A. the frequency changes.

• B. the amplitude changes.

• C. the wave speed changes.

• D. the new medium changes.

Practice

• The bending of a wave as it passes at an angle from one medium to another is called

• A. reflection.

• B. refraction.

• C. diffraction.

• D. interference.

Answer

• The bending of a wave as it passes at an angle from one medium to another is called

• A. reflection.

• B. refraction.

• C. diffraction.

• D. interference.

Sound

• All sounds are generated by vibrations.

• Sounds travel as longitudinal waves consisting of compressions and rarefactions.

• Sound waves travel in all directions away from their source.

• Sound waves require a medium through which to travel. Sound cannot travel in a vacuum.

• Your ears convert sound into electrical impulses that are sent to your brain.

• Exposure to loud sounds can cause hearing damage.

• Using earplugs and lowering the volume of sounds can prevent hearing damage.

Properties of Sound

• The speed of sound depends on the medium and the temperature.

• The pitch of a sound becomes higher as the frequency of the sound wave becomes higher. Frequency is expressed in units of Hertz (Hz), which is equivalent to waves per second.

• The Doppler effect is the apparent change in frequency of a sound caused by the motion of either the listener or the source of the sound.

• Loudness increases with the amplitude of the sound. Loudness is expressed in decibels.

• The amplitude and frequency of a sound can be measured electronically by an oscilloscope.

Sound requires a medium

• Alarm clock in a bell jar demo

How We Hear:

We lose the ability to hear higher pitches as we age.

Damage to any part of the ear can cause deafness.

The speed of sound depends on the medium and the temperature.

The pitch of a sound becomes higher as the frequency of the sound wave

becomes higher.

The Doppler effect is the apparent change in frequency of a sound caused by the motion of either the listener or

the source of the sound.

Loudness increases with the amplitude of the sound. Loudness is expressed in

decibels.