Waves Flashcards
Define waves
A wave is a periodic disturbance travelling through space, characterised by a vibrating medium.
What is a progressive wave?
Waves that carries energy from one place to another through a material or a vaccum are called progressive waves.
What are the two properties in which the movement of progressive waves is dependent upon?
Direction of propagation of energy (Wave).
Direction of Oscillation of particles of medium.
Define longitudinal waves.
If particles of medium oscillate parallel to to direction of propagation of energy the wave is longitudinal.
Define transverse waves.
If particles of medium oscillate perpendicular to the direction of propagation of energy the wave is transverse.
Define oscillation.
Repeated back and forth movements on either side of any equilibrium position.
An oscillation is a more specific term for vibration.
What is formed in longitudinal waves?
In longitudinal waves compressions and rarefractions are produced.
What are rarefractions?
Particles are further apart than their normal spacing. These regions have lower density and lower pressure than their normal values.
What are compressions?
Particles of medium are closer than their normal spacing. These regions have higher density than normal and pressure is at maximum.
What is formed in transverse waves?
Crests(top) and Troughs(bottom)
Define displacement:
The distance of a point on the wave from its undisturbed position or equilibrium position. Represented by x. Measured in m-meters.
Define amplitude:
The maximum displacement of a wave from the equilibrium position represented by A. Measured in m-metres. The greater the amplitude of the wave, the louder the sound.
Define wavelength:
Distance travelled while the particle of the medium completed on oscillation is called wavelength. Measured in metres and is represented by λ. note; when particle completes one oscillation wave travels exactly one wavelength.
What is the formula for speed of wave?
Speed of wave=Wavelength/Time Period
V= λ/T
But we know 1/T=F
So V= λ x 1/t
V=f λ
v=ms-1 v=m T=s
Define time period
Time period=Time taken for any wave to travel exactly one wavelength is called time period.
Time period=Total Time Taken/Number
Number can be of waves, crests, troughs, compression,rarefraction, oscillations, laps etc.
Define Frequency
The number of oscillations per unit time of a point in a wave. For sound waves, the higher the frequency of amusical note the higher the pitch.
Frequency=Number/Total Time
So, f=1/T or T=1/f or fT=1
Frequency=S-1=Hz
Number ofwaves crests troughs compressionrarefraction oscillations laps
What is a mechanical wave?
Waves are called mechanical waves if they need a substance (medium) through which to travel. For e.g. Sound
How can we measure frequency?
You can measure the frequency of sound waves using a cathode-ray oscilloscope (CRO) or oscilloscope for short. A microphone is connected to the input of the CRO. The microphone converts the sound waves into varying voltage that has the same frequency as the sound waves. The voltage is displayed on the CRO screen. Read in practicle activity 12.1.
What is phase difference?
The amount by which one oscillation of a particle leads or lags behind the other.
Phase difference=Δx/λ x 360
where x is distance between two consecutive crests or troughs
phase difference is measured in degrees or radians.
What is the phase difference of particles which are in phase?
0,360 and so on or 0 rad, 2π and so on.
What is the phase difference of particles which are anti phase?
Two particles oscillating in antiphase have a phase difference of 180,270 and so on or π rad, 3π. rad etc
path difference should be:
1/2 λ, 3/2 λ 5/2 λ
Define intensity
The intensity of a wave is describes as the rate of energy transmitted (power) per unit area at right angles to the wave velocity.
Intensity=Power/Area
where intensity=Wm-2
Power=watt W
Area=m^2
What is intensity dependent upon?
Intensity depends on distance from the source (d) I∝1/d^2
and amplitude of the wave (A) I∝A^2
What is the speed of sound?
The speed of sound is 330ms-1 in air at atmospheric pressure of 10^5 Pa and temperature 0 c.
Define dopplers affect.
Apparent change in frequency due to relative motion of source and reciever is called doppler’s effect.
there is no effect to the speed of sound. All waves get affected by this phenonemenon even electromagnetic waves.
Explain dopplers effect.
When the source moves towards the reciever, the reciever gets a higher frequency and smaller wavelength than actually produced by the source and if source moved way the receiver gets smaller frequency than actually produced by wave. (no effect to speed of sound)
