Waves

How measured? Wavelength: length of complete cycle Frequency: number of cycles per unit time Amplitude: distance covered by a particle

Two Types Transverse Wave Longitudinal Wave

Calculating frequency Measured in Hertz(Hz) Number of cycles per unit of time f = Number of cycles Total time Speed = frequency x wavelength

Ex. What is the frequency of the wave below? a)What is the frequency of the wave if this movement took 0.5 seconds? b) What is the speed of the wave?

a) f = 2 cycles/ 0.5 sec. f = 4 cycles/s b) Speed = frequency x wavelength = 4 cycles/s x 40 cm = 160 cm/s Do # 5 p. 11 7

1. Mechanical Waves Requires a medium to propagate Sounds waves: longitudinal & mechanical, decibel scale (db)

Sound Waves Variations in air pressure cause the sound wave to move through the air (medium) Ex. Loudspeakers, musical instruments, thunder

Frequency and sound - Sounds can have different tones Range of sound perception changes with each animal (see p.104) Low Frequency sounds = low pitched sound ex. Bass player High Frequency sounds = high pitched sound ex. Siren, birds chirping Unit of sound frequency : Hertz (Hz) Teen buzz- 14 400 Hz to 17 000 Hz (30’s & over: hard to hear over 8 000 Hz)

Amplitude Intensity of Sound depends on: The Amplitude (loudness of the sound) Measured in: decibels (dB) Sound tones: frequency in Hertz (Hz)

Decibel Scale Scale is a relative scale that represents the perception of the intensity of sound by the human ear. Measured: by a factor of 10 Each increase of 10, sound is 10 times louder Ex. Human breathing 10dB Soft music 50 dB 50-10= 40 So, 10 x 10 x 10 x 10 = 10 000 times louder!

2. Electromagnetic Waves Can travel in a vacuum or a medium. Includes visible light Includes radio waves, x-rays etc. Wavelength: short wavelength, higher frequency ( high energy!) ex. Gamma rays Long wavelength, lower frequency (low energy!) ex. Radio wave

Light Travels in straight lines(electromagnetic, transverse) An electromagnetic wave that is visible to the human eye.

Reflection 1. Diffuse reflection: uneven surfaces, scatter light

Specular reflection: - smooth surfaces - laws of reflection apply “angle of incidence=angle or reflection”

Real vs. Virtual Image Real image can be projected on a screen Virtual images cannot be projected on a screen

Refraction Light changes direction when it passes from one substance to another. (light is deviated as it passes) Why? - Speed of light depends of the medium it passes through - speed of light changes as it passes from air to water

Refracted light rays

Lenses Light refracts as it passes through lenses Two types of lenses

1. Converging lenses Brings light rays together Thickest at centre. Show light as ray in diagram Focal point real point where light meets at far side of lens Second Principal Focus: same distance on other side of lens

2. Diverging Lenses Spread light rays apart Thinnest at centre. Focal point: virtual point where light appears to emanate

Convex(converging) & Concave (Diverging)

How does this relate to the eye? Accommodation of crystalline lens of eye: a) far away object: - lens stretches, flatten - distant light rays don’t need as much refraction b) near object: - lens shortens, more spherical - light from near objects need to be refracted more

Corrective lens: a) myopia (nearsighted): diverging lens moves image back towards retina b) hyperopia (farsighted): converging lens moves images forward onto retina