Waves

Assesment 1

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  • Created by: katie
  • Created on: 01-10-14 20:22

Velocity

V=S/t

Velocity=speed/time

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Mechanical waves

Require a medium for transmission->no travel in a vaccume

Source vibrates->causes vibrations

Energy from vibrations->through medium(transmitted by particles within medium)

Transverse - Oscillations perpendicular to waves direction e.g water

Longitudinal - Oscillations parallel to waves direction e.g sound, within longitudinal waves are          Compressions->compact sections,   Refractions->spread out sections

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Oscillations

Repetative motion about a fixed point

At REST=at the extreme of motion(most compact or most streached)

At MAXSPEED=either midpoint of the oscillation

Oscillaions have 3 properties:

1.Amplitude

2.T the period(time of oscillation)

3.F frequency

F=1/T

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Displacement-time graphs->Oscillating particles

Two methods

1.Attach a pen to whats oscillating-> draws on card moving horizontally

2.Use a transmitter and reciever

Reading graph

hight=oscillation

period=wavelength

sinx graph=sinusodal

Waveform=shape of graph

Phase=position in cycle ->   1(t=0), 1/4(t=T/4),  1/2(t=T/2),  3/4(t=3T/4),  1(t=T=1)  ->1=1/2 but half is in antiphase like 3/4(moving in opposite direction to 1.

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Displacement-distance graphs

In a displacement distance graph it shows the position of all particles in a section of a wave in one instant(not one particles motion within the wave(displacement-time graph)).

Not all particles are in phase -> particles next to each other are at opposite positions.

Diagrams of longitudinal waves are very hard to draw this way. You can draw them as arrows in opposite directions, positive and negative displacements, (positive -> forward->like a peak)  (negative<-backwards<-like a trough

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Electromagnetic waves

Charged particles accelerated to cause electromagnetic waves.

Example - Radio waves -> electrons in ariel oscillate, this makes varrying electric and magnetic fields. Frequency=frequency of oscillation.

- variations in same plane as antenna(horizontal)

- variations at right angles to electric field oscillation(vertical)

Niether wave can exist without he other.

No medium needed.

To detect pass over charged particles, the particles pick up some of the energy and vibrate at the same frequency as the origional wave.

Can also occur due to 'quantum jumps' of electrons in atoms or from 'excited' nuclei -> these emit photons -> -packets of waves,  -only a few nano seconds in duration   -energy controls wavelength.

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Wave transmission

The speed of waves are different rates under different conditions:

Sound - 343ms^-1 @ 20 (c) in air, 

331ms^-1 @ 0(c), 

1497ms^-1 @ 25(c) in water

Light - 2.99792458x10^8 s^-1 in a vaccume,

2.99880297x10^8 ms^-1 in air

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Determening speed of light in different mediums

Precision- small incremants in measue

Accuraccy-how close to true value

SIN i/ SIN r= a constant

When a wav changes medium the speed changes this changes the distance it travels per wave so changes the waves direction. The only exception is if the beam is traveling on the normal line.

Wavelength=speed x time

oMg=Vo/Vg=speed of wave in first medium/ speed of wave in second medium

Refractive index: ratio of wave speed between two mediums

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Polarisation

A polarising filter blocks out oscillations, in all planes except one. If you use two at right angles to each other no waves can pass through.

Plane polarised = a transverse wave which only oscillates in one plane.

Reflected light is partially polarised.

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