4.4 Waves Flashcards
Define term progressive wave
Wave which transfers energy with a wave front which travels through a material
What is a transverse wave? And give an example
Particle oscillations are perpendicular to energy propagation
E.g electromagnetic waves
What is a longitudinal wave?
Particles oscillate in same direction as energy propagation
Rarefactions= low pressure
Compressions = high pressure
Define period and equation
Time taken for one whole wave cycle to be completed
Units : seconds
Period = 1/ frequency
Define frequency + equation
Number of wave cycles produced per cycle
Frequency = 1/time period
Units : Hz
Define phase difference
Difference in phase of 2 points on a wave or between 2 waves which have the same point or another definition could be the amount at which one wave lags another
Measured in degree or radians
Define path difference
Difference in distance travelled by 2 waves from their sources
Measured in terms of wavelength
What speed to EM waves travel at in a vacuum?
3.0 x 10 ^8 ms ^-1
What type of waves can be polarised?
Transverse waves
State the order of the EM spectrum
Radio, micro, infrared, visible light, UV , x-ray , gamma rays
Read my instructions visible under x ray glasses
Which EM wave has the longest wavelength and lowest frequency
Radio waves
Which EM wave has the shortest wavelength and highest frequency
Gamma rays
If speed is constant and the frequency increases then what happens to the wavelength
Decreases as frequency and wavelength are inversely proportional
Which EM wave is the most ionising
Gamma rays
Ionisation = electron removed from atom
Causes cancer and kills cells
So is most dangerous
State the uses for each EM wave
Radio : radio transmissions
Micro: TV transmissions
Infrared: night vision cameras
Visible light : heat detectors, optical fibres
Uv: security marks
X-rays : bone observation
Gamma rays: kills cancer cells, sterilisation of medical instruments
Approximate wavelength of each EM wave
Radio 10 ^3
Micro 10^-2
Infrared 10^-5
Visible light 0.5 x 10^-6
UV 10^-8
X-rays 10^-10
Gamma rays 10^-12
Equation for intensity using power and area
Intensity = power /area m²
What is the relationship between intensity and amplitude
Intensity is proportional to amplitude squared
What equation do you use for intensity and amplitude exam questions?
I/a² = I/a²
How do you know where to draw the normal
The normal should always be perpendicular to where the wave meets the boundary
State the Law of reflection
Angle of incidence =angle of reflection
Dur8ng refraction what happens when a wave enters a denser material
Wavelength decrease and speed of the wave decreases and so bends towards material
What is the optical density of a material measured by
Refractive index - ratio of the speed of light to speed of wave through a medium
Equation for refractive index (n)
n = c/v where c is constant 3 x 10⁸
State snell’s law
n x sin theta= n x sin theta
What is the critical angle
When a wave is travelling to a more dense material and the angle of refraction is equal to 90 ° which means the wave will refract along the boundary so the critical angle would be the angle that causes this refraction along the boundary.
How do you obtain total internal reflection?
When the angle if incidence is greater than the critical angle
What is the equation relating the critical angle
Sin C = n2/ n1
How does fibre optic Internet work
Infrared waves are sent down a glass/fibre core, as the angle of incidence is greater than the critical angle it is reflected into the glass rather than refracting through.
What is the principle of superposition of waves?
When two or more waves cross the resultant displacement is equal to the vector sum of the individual displacements
What is the principle of superposition of waves?
When two or more waves cross the resultant displacement is equal to the vector sum of the individual displacements
What does constructive interference mean?
Where the individual displacements are both in the same direction and results in a greater resultant displacement
What does destructive interference mean?
When the individual displacements are in opposite directions and are 180° out of phase from eachother which means they cancel each other out
