iGCSE Physics Section C

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Waves

Waves can transfer energy and information from one place to another. Energy and information are transferred by waves without transfer of matter.

TRANSVERSE: Travel at right angles to the direction of motion
LONGITUDINAL: Travel in the same direction as the motion.
(http://getting-in.com/wp-content/uploads/2012/11/Transverse-and-Longitudinal-Waves1.gif)

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Describing waves

Oscillate: move back and forth
Wavelength: distance between corresponding points on the wave
Amplitude: max displacement of a part of the medium from it's rest position
Period: time for one complete cycle of the wave to form
Frequency: number of cycles of wave form per second

(http://www.antonine-education.co.uk/Salters/MUS/images/Making6.gif)

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Waves equations

Frequency = 1/Period
Wavespeed = frequency x wavelength
(http://www.suntrek.org/images/speed-frequency-wavelength-.gif)

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Diffraction

Diffraction: The spreading of waves as they pass by obstacles.
                  Occurs with waves of ALL types

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Using Waves

Rules         Radiowaves         Increasing frequency
Make         Microwaves  
It                Infrared
Very          Visible light
Uneasy     Ultra violet
Xing          X rays
Girls          Gamma rays        Increasing wavelength

Visible light
Richard     Red                      Increasing frequency
Of             Orange
York          Yellow
Gave         Green
Battle        Blue
In              Indigo
Vain          Violet                   Increasing wavelength

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Using waves cont. Analogue and digital.

The speed of all electromagnetic waves are constant
Higher frequency=Shorter wavelength.

Digital and analogue
Analogue electrical signals are continuously variable voltages
 - must be amplified
 - pick up 'noise'
Digital electrical signals can have only two possible values 0 and 1 (binary number system)
 - Regenerated
 - more information can be transmitted.

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Light waves

Reflection of light
normal: at right angles to the mirror surface where the light rays strike at it.
i: angle of incidence r: angle of reflection

Law of reflection:
The angle of incidence = the angle of reflection

An image on a mirror is a virtual image. It appears to be the same distance behind the mirror as it is infront.
Refraction of light
When a light ray travels from air into glass it is bent towards the normal and when a light ray travels back out of glass into air, it is bent away from the normal.

Law of refraction:
refractive index, n = sin i / sin r OR 1/ sin c

Critical angle, c: the angle at which the reflection travels at a 90degree angle to the normal.

Refraction is used in optical fibres.  Light can be diffracted.

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Sound Waves

Sound travels as a longitudinal eave through gases, liquids and solids. They cannot travel through a vacuum. The speed of sound in gases is lower than in liquids and slower in liquids than solids.

Humans can hear 20Hz to 20kHz. These frequencies are known as audio frequencies.

Stethoscopes are an example of total internal reflection of soundwaves.

Pitch: how quickly the sound producer is vibrating: T=1/f

Oscilloscopes
use small voltages that vary with time in the same way as the changing pressure of the air. It produces a graph to show how the voltages are changing with time. The greater the loudness, the higher the amplitude.

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