WavesSound and Light

Cambridge IGCSE

Transverse waves• Definition:A wave in which the direction of displacement is perpendicular to the direction of propagation, as a surface wave of water. Eg. Light

Longitudinal waves

• Definition A wave in which the direction of displacement is the same as the direction of propagation, as a sound wave. Eg. Sound

Definitions

• Wavelength (λ): The distance, measured in the direction of propagation of a wave, between two successive points in the wave that are characterized by the same phase of oscillation. SI unit is the metre (m).

Definitions

• Frequency (F)The number of cycles or completed alternations per unit time of a wave or oscillation. SI unit-hertz (Hz)

Definitions

• Amplitude (A)The absolute value of the maximum displacement from a zero value during one period of an oscillation.SI unit is the metre (m).

In transverse waves, this is half the crest-to-trough height

Definitions

• Period (T): This is the time taken for one point on the wave to complete one oscillation. Or you can think of it as the time taken to produce one complete wave. The SI unit is second (s).

The distance the wave travel’s in 1 secondThe speed is dependant on the substance or medium in which the wave is passing through

the absolute value of the maximum displacement from a zero value during one period of an oscillation.

Waves transfer energy and information

• You can feel the energy in infra-red waves from the sun

Waves transfer energy and information

• See the energy contained in the oceans waves

Waves transfer energy and information

• See the information contained in the light reaching your eyes

Waves transfer energy and information

• Waves are vibrations that transfer energy through a medium without causing the individual particles of a medium to move significantly from their equilibrium or position of rest.

Formula v = f x λ

Reflection

• Def: the waves will always reflect in such a way that the angle at which they approach the barrier equals the angle at which they reflect off the barrier.

Refraction

• Def: waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.

Diffraction

• Def: a change in direction of waves as they pass through an opening or around a barrier in their path. Water waves have the ability to travel around corners, around obstacles and through openings.

Wave interference

• Occurs when two waves meet while traveling along the same medium.

Light

Def: The movement of light conceptualized as a wave, defined by such properties as reflection, refraction, and dispersion

Visible light is a form of electromagnetic (EM) radiation, as are radio waves, infrared radiation, ultraviolet radiation, X-rays and microwaves. Generally, visible light is defined as the wavelengths that are visible to most human eyes.

• Light travels in a straight line• Speed of light 299,792 kilometers per second• Polarized light has vibrations confined to a

single plane that is perpendicular to the direction of motion

• As light enters your eyes, it is refracted by the lens in your eye and brought to focus on your retina

Reflection of light

• Virtual image: laterally inverted image

• Angle of incidence (i) = Angle of reflection (r)• Normal: A perpendicular line can be drawn to

the surface of the mirror, at the point of incidence where the ray strikes the mirror

Refraction • occurs as light passes across the boundary

between two media

Snell’s law

• Refraction index• n = sin i / sin r• n = Speed of light in medium 1

Speed of light in medium 2

• Critical angle: – The angle of refraction becomes equal to 90°

• Total internal reflection:– At greater angles of incidence, the ray are entirely

reflected back inside the medium

Optical fibres

Uses of Converging Lens

Three rules of refraction

• Any incident ray traveling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens.

• Any incident ray traveling through the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.

• An incident ray that passes through the center of the lens will in effect continue in the same direction that it had when it entered the lens.

Dispersion of light

• The separation of visible light into its different colours

Electromagnetic Spectrum

Sound

• A wave pattern of disturbance caused by the movement of energy traveling through a medium as it propagates away from the source.

• The source is some object that causes a vibration.• The vibration disturbs the particles in the surrounding

medium; those particles disturb those next to them, and so on.

• The wave carries the sound energy through the medium, usually in all directions and less intensely as it moves farther from the source.

What can you hear? • Acoustic sound 20Hz to 20 000Hz• Ultrasound higher then 20 000Hz• Infrasound lower than 20Hz

Measuring the speed of sound • Use two microphones and a fast recording

device ( Oscilloscope) • x = the distance between the microscopes• t= time difference between signals (delay)• Speed of sound = x/t

Loudness & Pitch

• We are all used to hearing different sounds. We describe the differences in various ways: loudness (loud, noisy, quiet, etc.) and high or low pitch.

• The taller the amplitude, the louder the sound. The more waves there are displayed, the higher the pitch. Let's look at this in more detail.

Echoes & Reverbation

• Reflection of sound waves off of barriers result in some observable behaviours

• Perception of a sound usually endures in memory for only 0.1 seconds

• Echo- more than 0.1 seconds (there will be a small time delay)

• Reverb -less than 0.1 seconds (sound wave is still held in memory, there is no time delay)

Uses of sound

Doppler’s effectThe Doppler effect can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequencyfor observers towards Whom the source is Approaching and an apparent downward shift in frequency for observers from whom the source is receding.

References

• http://www.dictionary.com/browse/transverse-wave

• https://www.berkeley.edu • http://www.physicsclassroom.com/class/wave

s/Lesson-3/Reflection,-Refraction,-and-Diffraction

• http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway_pre_2011/energy_home/5_light1.shtml

References

• http://askmichellephysics.blogspot.co.za/2012/04 /properties-of-waves.html

• http://whatis.techtarget.com/definition/sound-wave