1 Sound & Light Chapter 15

2 Sound  Sound waves are caused by vibrations, and carry energy through a medium.  Sound waves are longitudinal waves.  Speed of sound depends on the medium.

3 Speed of Sound  Speed of sound at room temperature is about 346 m/s.  An increase in temperature increases the speed of sound.  Sound waves travel faster in liquids & solids than gases.

4 Loudness determined by Intensity  Intensity of a sound wave describes the rate at which a sound wave transmits energy through a given area of the medium.  Loudness depends on the intensity of the sound wave.  The greater the intensity, the louder the sound.

5 Relative Intensity  The relative intensity of sounds is found by comparing the intensity of a sound with the intensity of the quietest sound a person can hear.  Relative intensity is measured in units called decibels.

6 Pitch  The pitch of a sound is related to the frequency of sound waves.  High pitch correspond to a high frequency, and low pitch corresponds to a low frequency.

7 What type of wave is sound? A. longitudinal B. seismic C. surface D. transverse

8 Human Hearing  Infrasound is sound that has a frequency below human hearing.  Ultrasound is sound that has a frequency above human hearing.

9 Musical Instruments  Fundamental frequency is the frequency of a standing wave which wavelength is twice the length of a string on an instrument.  Instruments vibrate at their fundamental frequency and whole-number multiples of that frequency called harmonics.

10 Instruments Amplify Sound  Vibrations from plucking strings of an instrument are called forced vibrations.  The body of a guitar vibrate at certain specific frequencies called natural frequencies.

11 Resonance  Resonance is when an instrument vibrates at its natural frequency.  The natural frequency of an object depends on its: Shape Size mass

12 Hearing  Sound passing through the outer ear to the middle ear.  The middle ear consists of the hammer, anvil & stirrup.  The middle ear vibrates the fluids in the cochlea.  The cochlea has tiny hairs that are stimulated and transmit the impulses to the brain.

13 Application of Sound  Sonar is a system that determines distance by measuring the time it takes for sound waves to be reflected back from a surface.  Ultrasound is a device that uses the echoes of high frequency ultrasound to produce images of internal organs.

14 Assignment:  Design an musical instrument from materials you have at home.  Classify it as a woodwind, brass, percussion or string instrument.  Be able to explain the theory behind the instrument playing different tones.  Be able to present music and play it on the instrument in a recognizable way.  Due Monday.

15 Light as a Wave  Light travels as transverse waves.  Light does not require a medium.  Light waves are called electromagnetic waves.  The wave model is supported because light can reflect, refract and diffract.

16 Light as a Particle  In the particle model, light travel in photons.  Photons are considered particles.  Photons don’t have mass, they are bundles of energy.

17 Frequency of Light  The amount of energy is proportional to the frequency of the corresponding electromagnetic wave.  A photon with twice as much energy corresponds to a wave with twice the frequency is in the ultraviolet range.  A photon with half as much energy corresponds to a wave with half as much frequency is in the infrared range.

18 Speed of Light  Light travels at the speed of 300,000 km/s.  Light travels fastest in a vacuum and slower in any medium.  Nothing travels faster than light in our universe.

19 Intensity of Light  The brightness of light depends on the intensity of the light.  Intensity depends on the amount of light that passes through a certain area of space.  Light spreads out from the source. The farther from the light source, the dimmer the light.

20 Electromagnetic Spectrum  Electromagnetic spectrum consist of light of all possible energies, frequencies and wavelengths.  Ultraviolet light has higher energy and shorter wavelengths than purple light.  X-rays has higher energy and shorter wavelengths.  Gamma rays has the highest energy and shortest wavelengths.

21 Electromagnetic Spectrum continued  Infrared waves has wavelengths slightly longer than red light.  Microwaves are used for cooking.  Radio waves have the longest wavelengths.  Radar is used to determine location.

22 Reflection and Color  Reflection occurs as light hits a barrier and bounces off of the barrier.  The incidence ray is the incoming light waves.  The reflected ray is the light waves that bounce off of the barrier.

23 Reflection (continued)  The angle of incidence is defined by the angle between the normal and the incidence ray.  The angle of reflection is defined by the angle between the normal and the reflected ray.  The law of reflection states that the angle of incidence is always equal to the angle of reflection.

24 Types of Reflection  Smooth reflection occurs when the light waves hit a smooth surface.  Diffuse reflection occurs when the light waves hit a rough surface and the light waves are scattered.

25 Types of Mirrors  Concave mirrors are mirrors that curve inward. These type of mirrors can produce virtual & real images.  Convex mirrors are mirrors that bulge outward. These type of mirrors can produce virtual images.  Plane mirrors produce virtual images.

26 Type of Images  Real images are inverted images formed where rays of light meet.  Virtual images are upright images formed where rays of light appear to meet or come from.

27 Colors  The color we see is the light being reflected from the object.  Additive primary colors are red, green & blue.  Subtractive primary colors are yellow, cyan and magenta.

28 Colors and Pigments  If all colors are reflected, you see white light.  If all colors are absorbed, you see black.

29 Refraction  Refraction happens when light waves changes speed as it goes through different mediums.  As light waves change speed the waves bend.

30 Effects of Refraction  Refraction makes objects appear to be in different positions.  Refractions in the atmosphere creates mirages.

31 Snell’s Law  Snell's Law Snell's law (also known as Descartes' law or the law of refraction), is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves, passing through a boundary between two different media, such as air and glass.formulawaves media

32 Total Internal Reflection  If the angle at which light rays meet the boundary between two mediums becomes small enough, the rays will be reflected as if the boundary were a mirror.  This angle is called the critical angle, and this type of reflection is called total internal reflection.

33 Lenses  A lens is a curved piece of glass.  Lenses can magnify images.  Magnification is any change in the size of an image compared with the size of the object.

34 Type of Lenses  Converging lens bends the light inward that produces a virtual or real image. (convex lens)  Diverging lens bends the light outward and can produce only a virtual image. (concave lens)

35 Prisms  Prism is a triangular shaped piece of glass that refracts light.  Prism disperse light.  Dispersion is the separation of light into separate colors because of the differences in wave speed.