Module 4.4 - Waves Flashcards by Siobhan Woolley

Define progressive wave

A wave that transfers energy away from a source

How well did you know this?

Not at all

Perfectly

Define wavelength

The smallest distance between one point on a wave and the identical point on the next wave

How well did you know this?

Not at all

Perfectly

Define period

Time taken for one complete pattern of oscillation

How well did you know this?

Not at all

Perfectly

Define frequency

The number of oscillations per unit time

How well did you know this?

Not at all

Perfectly

Define displacement

The distance travelled in a particular direction by a wave from its mean or rest position

How well did you know this?

Not at all

Perfectly

Define amplitude

The maximum displacement of a wave from its mean or rest position

How well did you know this?

Not at all

Perfectly

Define phase difference

The difference (in radians) in the phases of two waves of the same frequency

How well did you know this?

Not at all

Perfectly

Define path difference

The difference (in metres) between the distances travelled by two waves arriving at the same point, in relation to the wavelength

How well did you know this?

Not at all

Perfectly

Define intensity

The rate at which energy is transferred from one location to another as the wave travels through space, perpendicular to the direction of wave travel

How well did you know this?

Not at all

Perfectly

Define reflection

When waves rebound from a barrier, changing direction but remaining in the same medium

How well did you know this?

Not at all

Perfectly

Define refraction

When waves change direction when they travel from one medium to another due to a difference in the wave speed in each medium

How well did you know this?

Not at all

Perfectly

Define diffraction

When a wave spreads out after passing around an obstacle or through a gap

How well did you know this?

Not at all

Perfectly

Define interference

The addition of two or more waves that results in a new wave pattern due to the principle of superposition

How well did you know this?

Not at all

Perfectly

Define electromagnetic wave

A self-propagating transverse wave that does not require a medium to travel through

How well did you know this?

Not at all

Perfectly

Define polarisation

The process of turning an unpolarised wave into a plane-polarised wave

How well did you know this?

Not at all

Perfectly

Define plane-polarised wave

A transverse wave oscillating in only one plane

How well did you know this?

Not at all

Perfectly

Define polarising filter

Produces a plane-polarised wave of light by selective absorption of one component of the incident oscillations
The filter transmits only the component of light polarised perpendicular to that direction

How well did you know this?

Not at all

Perfectly

Define refractive index

A value that indicates how quickly or slowly EM radiation will travel through a medium

How well did you know this?

Not at all

Perfectly

Define total internal reflection

When EM radiation travels from a material of a higher refractive index to one of a lower refractive index and the angle of incidence is larger than the critical angle

How well did you know this?

Not at all

Perfectly

Define critical angle

The angle of incidence when the angle of refraction is 90°

How well did you know this?

Not at all

Perfectly

What is the principle of superposition?

It states that when two or more waves of the same type meet, the resultant wave can be found by adding the displacements of the individual waves

Define constructive interference

Occurs when two waves meet in phase

Define destructive interference

Occurs when two waves arrive at a point out of phase

Define coherent

Two waves with a constant phase relationship

Define diffraction grating

A piece of optical equipment made from glass, onto which many thousands of very thin, parallel and equally spaced grooves have been accurate,y engraved using a diamond

Define order

The number of the pattern (n) on either side of the central maximum

How to calculate period from an oscilloscope

Distance between peaks x time base setting

What does it mean if two waves are in phase?

Exact same pattern of oscillation | No phase difference

What does it mean if two waves are in antiphase?

Exact opposite pattern of oscillation | Half a cycle phase difference

How to covert from degrees to radians

Divide by 180 | Multiply by pi

How to convert from radians to degrees

Multiply by 180 | Divide by pi

How to derive the wave equation

Speed = distance / time In one period, T, wave travels one wavelength: v = wavelength / T F = 1 / T, so substitute f for 1 / T V = wavelength x frequency

Why is intensity proportional to the amplitude squared?

The amplitude of a wave decreases as the wave spreads out from a source Energy of a wave is proportional to the amplitude squared Therefore intensity is also proportional to the amplitude because intensity relates to energy transfer

When is diffraction shown the most clearly?

Wavelength of diffracted wave is equal to gap that it is travelling through

Law of reflection

Angle of incidence = angle of reflection

Snell’s Law

n1 x (sin x incident angle) = n2 x (sin x refracted angle)

Formula for critical angle

sin x critical angle = n2 / n1 n1 = refractive index of more dense medium n2 = refractive index of less dense medium

What happens when the angle of incidence is less than the critical angle?

The ray is refracted with very little reflection

What happens if the angle of incidence is equal to the critical angle?

The ray emerges along the edge of the block

What happens if the angle of incidence is greater than the critical angle?

The ray is totally internally reflected

Conditions for total internal reflection

Angle of incidence must be greater than the critical angle | Incident substance must have larger refractive index

Applications of total internal reflection

Fibre optics to send information (often telephone calls or internet access) at the speed of light through a fibre optic Quicker and can carry more information

Diffraction if the gap is smaller than the wavelength?

No diffraction | Waves are reflected by barrier

Diffraction if width of gap is similar to wavelength?

Diffraction occurs

Diffraction if width of gap is equal to wavelength?

Maximum diffraction

Diffraction if width of gap is larger than wavelength?

Slight diffraction at waves’ edges

Similarities between progressive and stationary waves

Neither transfers matter | Both can be longitudinal or transverse

Differences between progressive and stationary waves

Progressive transfers energy in direction of propagation - for stationary there is no transfer of energy For progressive, all points are out of phase along one wavelength (e.g. crest and trough by 180°) - for stationary, points between 2 nodes or an even number of nodes are in phase, points between an odd number of nodes are in antiphase For progressive, all particles have the same amplitude - for stationary, amplitude varies according to position (0 at nodes)

What does the frequency of the vibrations on a string depend on?

Mass per unit length Tension Length of the string

Define the fundamental mode of vibration

The length of the string is half the wavelength, producing the lowest possible frequency (first harmonic)

Define harmonics

Whole number multiples of the fundamental frequency of a stationary wave

Describe an experiment to determine the speed of sound in air

Use a tuning fork of a known frequency and a tube of water held by a clamp so its length can be altered When the tuning fork is struck above the tube of water, a stationary wave will be set up in the tube The fundamental frequency can be obtained by listening carefully and finding the minimum length at which the sound is loudest (when the length of the tube is equal to a quarter of the wavelength) Lengthen the tube and the sound will decrease in volume before reaching its second maximum loudness The difference between these two lengths is half a wavelength, so multiply by 2 to find the speed of sound in air