Physics - Waves

Wave

A periodic oscillation that transfers energy form one point to another

-Pulse: A wave or disturbance that is not repeated

-Periodic: A wave or disturbance that is repeated

Vibration/oscillation

A forward/backward motion in a straight line or along an arc (e.g. pendulum or spring)

Cycle

One complete vibration in a periodic motion

Period

Time taken for one complete cycle of a wave (T)

Wavelength

Distance between two successive points on a wave (i.e. between two crests or troughs) (λ)

Frequency

Number of complete cycles that pass a given point over a certain time period (hertz - hz)

Amplitude

Maximum displacement of a particle from it’s rest position (i.e. the crest or trough of a wave)

Mechanical wave

Requires a physical medium for energy to travel

-e.g. water, sound

Electromagnetic wave

Requires no physical medium for the energy to travel

-e.g. Light energy (photons) or radiation (also photons)

Medium

Substance a wave moves through

Transverse wave

oscillations that are perpendicular to velocity of wave

-Most waves

-Light/electromagnetic radiation is transverse

Longitudinal wave

Oscillations that are parallel with the velocity of the wave

-Sound is most common example

Sound waves

Sound waves are longitudinal and involve:

-Compression: Air gets squished together and there are more particles in a smaller space

-Rarefaction: Air gets less dense with particles and spread out more

They are mechanical and require medium to travel

-Travels fastest through solids as particle are more tightly packed allowing sound waves to transmit more efficiently and quickly

-330-350m/s

Light waves (EM spectrum)

-Transverse

-Type of EM wave is determined by the wavelength/frequency (longer wave, lower frequency

-300000000m/s

Displacement vs time

Can find:

-Amplitude

-Frequency

-Period

Displacement vs distance

Can find:

-Amplitude

-Wavelength

Doppler effect

describes the change in frequency or wavelength of a wave as perceived by an observer when the source and observer are moving relative to each other

Reflection

occurs when a wave changes direction at the boundary between two mediums, returning to the medium it starts in

Fixed boundaries

 the wave will be reflected and inverted when returning back. This is also called a phase reversal (the phase switches – i.e. peaks become troughs)

Free boundaries

the wave will be reflected back in the same way as the incident wave

Reflected waves law

The angle of incidence of wave (from the normal) will be equal to the angle of reflection of the reflected wave.

Refraction

Refraction is when waves ‘bend’ as they move from one medium to another

-Speed and wavelength can change (slower wave, shorter wavelength

Angles of refraction

1.If wave slows down - bends towards normal

2.If wave speeds up - bends away form the normal

BEING SLOW IS NORMAL

Speed of sound is dependent on…

1.Elasticity (or stiffness)

-Measure of how easily something will return to its og shape (solid>liquid>gases)

2.Density

-How closely packed particles are together (solids>liquid>gases)

Refraction of waves: light

Light will travel slower as density increases, hence:

-Solid will be slowest, gas the highest

-Light will refract towards normal if it goes into a denser material as it slows down

Refraction of waves: sound

Sound will travel faster as density increases

-Sound will be fastest, gas the lowest

-Sound will refract away from the normal as it goes into a denser material as it will speed up

Behaviour after refraction (if wave speeds up)

-the angle of refraction is greater than incidence (bends away from normal)

-Wavelength will increase

Behaviour after refraction (if wave speeds up)

-Angle of refraction is smaller than incidence (bends towards normal)

-Wavelength will decrease

Diffraction

-The spreading of waves when it encounters a barrier or a slit/gap

-Bigger the gap - the less diffraction and vice versa

-Lower frequency and longer wavelength the better a wave tends to diffract