Chapter 11 Waves 1 & 2 Flashcards
Amplitude
Maximum displacement from the equilibrium position in a particular direction.
Displacement
Distance from the equilibrium position of a POINT in a particular direction. It is a vector so can have a negative value also.
Wavelength
Minimum distance between two points in phase on adjacent waves.
Frequency
The number of wavelengths passing a given point per unit of time.
Period
Time taken to complete 1 wave.
Wave equation
Velocity = frequency x wavelength
Wave speed
Distance travelled by the wave per unit time.
Phase difference
Difference in displacements in particles on a wave
Progressive wave
A progressive wave is a wave that can travel through matter or through a vacuum and carries energy from one place to another.
Longitudinal wave
Waves that travel through a medium and create rarefactions and oscillations and oscillate parallel to the direction of motion.
Transverse wave
A transverse wave oscillates perpendicular to the direction of travel.
Examples of transverse waves
All electromagnetic waves
s waves in earthquakes
Examples of longitudinal waves
P waves from an earthquake
sound waves
What is it called when two particles are oscillating 180 degrees out of phase?
Antiphase
What is Refraction?
Refraction is when a wave passes through a more/less optically dense medium and changes wave speed, bending the waves either towards or away from the normal depending on the density of the material it is entering.
What is reflection?
Reflection is when a wave changes direction at a boundary between two different mediums, remaining in the original medium.
What is the law of reflection?
Angle of incidence = Angle of reflection
Where is the angle of incidence measured from?
It is measured from the normal.
How do you calculate the refractive index of a material?
n = Speed of light in a vacuum/speed of light in the solid
or snells law N1 sin theta1 = N2 sin theta2
What are the conditions needed for total internal reflection to occur?
The wave needs to be going from a more to a less dense medium
The wave needs to have an angle of incidence greater than its critical angle
What is the critical angle?
The critical angle is the angle which a wave enters a medium giving an angle of refraction of 90 degrees.
Where is total internal reflection helpful?
Total internal reflection is used in optical fibres.
Superposition of waves
When two waves of the same type meet at a point.
Interference
When two wave paths cross over each other, producing a resultant wave, possibly destructively or constructively.
Coherence
When two wave sources or waves have constant phase difference.
Path difference
The difference between the displacements of two waves from different sources to the same point.
How to calculate the resultant amplitude of two waves interferring?
Amplitude 1 + Amplitude 2
What are maxima and minima?
These points are points where waves interfere constructively (maxima) and destructively (minima).
What is diffraction?
Diffraction is the process by which waves spread out as a result of passing through a narrow gap forming an interference pattern.
What is the equation when using young’s double slit experiment?
Wavelength = (distance between slits x distance between maxima) / Distance between board and slits.
This equation only works when a is lot smaller than D.
What is polarisation of waves?
Polarisation of waves is when the wave is only oscillating in one direction perpendicular to the direction of energy transfer and cannot pass through a filter which is the wrong way around.
How to change the wave speed of a wave in a ripple tank?
make the water deeper
Why can even when there is a slit in a material does diffraction not occur?
When the gap is either too small or too big and either passes through normally or is reflected normally.
Explain how a stationary wave is formed with a rope fixed at one end?
The rope oscillates up and down and forms a wave which reflects off the fixed end and this reflection causes constructive and destructive interference causing nodes and antinodes to form
Definition of antinode?
This point forms when two waves interfere constructively with the same frequency
The point with the greatest amplitude and therefore intensity
Definition of Node?
A point on a stationary wave where the amplitude is always 0 and is because the waves interact with each other destructively.
What is the order of the electromagnetic spectrum?
Raging
Martians
Invade
Venus
Using
Xray
Guns
What are the conditions needed for the double slit experiment to work?
The waves must come from a coherent wave source, the slits must be close enough together to overlap and cause interference and the slits must be narrow enough than diffraction occurs.
What is the difference between an emission line spectrum and an absorbtion line spectrum?
In an absorbtion line spectrum a series of dark lines appear on a bright background.
What phenomena apply to both electromagnetic and sound waves?
Refraction and diffraction and reflection
How to calculate the amplitude and wavelength of a longitudinal wave?
The amplitude can be calculated by finding a point which oscillates the most and finding the maximum distance it has moved.
To find the wavelength you can find the distance between the middle of two consecutive compressions.
What is the equation for intensity?
Intensity = power / cross sectional area
What happens to the intensity of a wave as it gets further away from the source?
The intensity decreases as the distance from the source increases. it has an inverse square relationship. if the distance increases by a factor of 100 the intensity will be 10000 times smaller.
What to remember when using cross sectional area of a planet?
The area is the surface are not the circle. It is a sphere
What is intensity proportional to?
Intensity is proportional to the amplitude squared.
What makes an electromagnetic wave different to other transverse waves?
They have electric and magnetic fields oscillating perpendicular to each other.
How much does each phase difference change from the central maxima?
It changes by a wavelength (in radians/degrees)
How much does each path difference change by from the central maxima between maximas?
1 wavelength
Describe the phase difference between the two waves that form a stationary wave at a node and at an antinode?
Node: out of phase
Antinode: in phase
What happens to the wavelength, wave speed and frequency when a wave passes from a medium of lower to higher refractive index?
Wavelength decreases and so does wave speed as frequency is constant
