Waves and Optics Flashcards
What is the equation for threshold frequency?
f_0 = ϕ/h
What happens when a light ray moves into a more optically dense medium?
The light ray bends towards the normal line.
What happens when a light ray moves into a less optically dense medium?
The light ray bends away form the normal line.
What are the conditions for total internal reflection (TIR) to occur?
The ray would be moving into a less optically dense medium if TIR didn’t occur and the angle of refraction must be greater than 90 degrees.
What is path difference?
The amount by which the path travelled by one wave is longer than the path travelled by the other wave.
What is phase difference?
The difference in the phase angle between two waves.
What is the equation for the speed of a wave?
V = fλ
What are the equations for the wavelength of a standing wave in the 1st, 2nd and 3rd harmonic?
1st: λ = 2l
2nd: λ = l
3rd: λ = 2l/3
What is the equation for tension in a string creating a standing wave?
T = mg
what is the equation for μ?
μ = m/l (mass per unit length)
What is the single slit used for in young’s double slit experiment?
To keep the waves coherent.
What are light and dark fringes?
Light fringes are caused by light waves in phase superposing and interacting constructively. Dark fringes are caused by light waves in antiphase superposing and interacting destructively. There is still light in dark fringes, it is just cancelled out by destructive interference.
Define the terms in the equation for fringe spacing:
w = λD/s
w is fringe spacing, λ is wavelength, D is distance from the slits to the screen and s is slit spacing measured from the centre of each slit.
What is a node?
A stationary point on a standing wave caused by destructive interference of two waves superposing in antiphase.
What is an antinode?
A point of a standing wave where displacement is maximum. This is caused by constructive interference between two waves superposing in phase.
What is the equation for refractive index?
n = c/v where n is the refractive index, c is the speed of light in vacuo and v is the speed of light in the material.
What is Snell’s law?
n = sin θ_I/sin θ_R
What is the equation for the law of refraction?
n_1 sin θ_I = n_2 sin θ_R
What is the critical angle?
Where the angle of refraction is 90 degrees.
What is the equation for a diffraction grating?
d sin θ = n λ where d is the slit spacing, n is the order number and λ is the wavelength.
What is the equation for lines per meter in a diffraction grating?
1/d where d is slit spacing.
How do you convert lines per millimetre on a diffraction grating into lines per metre?
Multiply lines per millimetre by 10^3 then take the reciprocal.
Why are there black lines on an absorbtion spectrum?
Because excited gas atoms absorb the photons of the wavelengths of the blackspaces.
Define the terms in the equation for the first harmonic:
f = 1/2l √(T/μ)
f = frequency of oscillation l = length of the string T = Tension in the string μ = mass per unit length of the string
How does increasing the slit width affect the amount of diffraction and the intensity of the central maximum?
Decreases diffraction, increases intensity of the central maximum.
How does increasing the wavelength affect the amount of diffraction and intensity of the central maximum?
Increases diffraction, lowers intensity of the central maximum.
How does using a diffraction grating instead of just two slits affect the diffraction pattern?
Same shape but bright bands are brighter and narrower and the dark areas between are darker. The pattern is really sharp which allows for more accurate measurements.
What do the maxima look like from monochromatic light?
Monochromatic, sharp lines.
What do the zero, first and second orders look like from the diffraction of white light?
The zero order (middle) is white then the first order is a clear rainbow then the second order is a wider, more faded rainbow etc.
How does the refractive index of a material affect the speed of light within it?
The higher the refractive index is, the slower the light is within it.
What is modal dispersion?
When light rays enter the fibre at different angles so take different paths so reach the end in different amounts of time.
What is material dispersion?
When light rays reach the end of the fibre at different times due to their differing wavelengths.
