Thursday PS 1-3

Homework

Light

Sound

HomeworkPg 478

1) Describe what may happen when ripples on a pond encounter a large rock

2) Explain why you can hear two people talking even after they walk around a corner?

3) Name the conditions required for two waves to interfere constructively

HomeworkP 478

4) Explain why colors appear on a soap bubble

5) Draw a standing wave, and label nodes and antinodes

6) What conditions are required for two waves to interfere completely destructively? (there are 4)

Answers

1) Reflection

2) Diffraction, as they pass the corner of hall

3) Waves must be in same place (meet). Crest meets crest or trough meets trough

Answers

4) Two sets of reflected waves from bubble meat, some constructively, others destructively changing the wavelength of light. Different colors result from different wavelengths

5) 6) Waves must match in amplitude,

frequency and crest must match up with trough

Correction

• Colors can be formed by either constructive or destructive interference

• As long as the combined frequency falls within the range of visible light

• Different frequencies of light produce color

Iridescence

• Also formed as a result of interference between 2 or more waves of light

• Liquid crystal thermometers• Wings of butterflies• Tail of a peacock• Bird feathers• Beetles shell

Examples of Iridescence

More examples of iridescence

Sound

• Wave type –Longitudinal

• Speed of Sound • 331m/s @ 0°C to 386 @ 25C• 1490-1530 C in water• 3800-5000 C

• Speed of sound is effected by temperature, and type of medium

Other measurement of sound

Intensity

Loudness

• Depends on the energy in the sound wave

• Intensity = rate of energy transmission through a given area of the medium

• Greater Intensity Louder sound

Measure of Loudness

• Relative intensity

• Compares the intensity of the sound with the intensity of the quietest sound that a person can hear

• Measured in decibels

Decibel scale

• 0 dB threshold of hearing

• 30 dB whispering

• 50dB normal conversation

• 70dB vacuum cleaner

• 90 dB lawnmower

• 120 dB threshold of pain

• 150 dB nearby jet airplane

http://www.fotosearch.com/comp/phd/phd528/two-women-whispering-into-mans-ears-close-up-~-200023765-001.jpg

Pitch

• Not related to loudness

• Related to the frequency of wave

• The higher the frequency

higher the pitch

• Humans can hear a range of sound from 20 HZ to 20,000 HZ

Sound beyond human range

• Lower than 20 Hz Infrasound

• Higher than 20,000 Hz ultrasound

• Dogs can hear to 46,000 Hz

• Dolphins can hear to 150,000 Hz

Elephant communication

• Use infrasound waves between 6-18Hz

• Few objects can absorb the energy carried by these frequencies

• Sounds heard across far distances

Echo-location

• Dolphin sends out a series of audible clicks.• They bounce off an object and reflect back to

dolphin, received by 2 ears• Through experience, dolphin relates time,

strength of signal into distance

Other animals to use echo-location

Musical Instruments

• Produce sound by vibrating strings, air columns or membranes

• Changing where you press on a string, The length of the air column changes the frequency, and pitch

• Standing waves produce the continuous sound, • Notes created at certain wavelengths

Echos

• What is needed to create an echo?

Place where you hear an echo the most?

Example of Ultrasonic sound waves

• 1 to 15 million Hz• Passes through most

materials, but reflects at medium boundaries

• Not harmful like x-rays

Used more frequently for other purposes

                                  

    

Why use ultrasonic waves?

• Focused into more narrow beams

• Directed more easily

SONAR

• Sound, Navigation, and RAnging

• Uses acoustic signals and echo returns to locate objects

Sonar

Homework

Pg 498

Problems 1-5 and #9