U3 - Optics Flashcards
What is refraction?
When a wave changes direction as it moves from one medium into another.
What remains constant
under refraction?
Frequency
Which wavelength refracts
more?
A shorter wavelength
What is absolute refractive
index?
How many times slower the speed of light is in a medium compared
to the speed of light in a vacuum.
n = cv / cs
where cs is the speed of light in substance
What is Snell’s Law?
n1sinθ1= n2sinθ2
What is the refractive index
of air?
Approx. 1
What happens when the
incident angle = the critical angle?
The angle of refraction is 90° so wave travels along the boundary
Give two conditions needed
for total internal reflection to
occur?
● Light must be travelling from a more dense to a less dense
medium.
● The angle of incidence ≥ critical angle.
Why is a semi-curricular
block often used for total
internal reflection?
As you want the curved side to have an angle of incidence of 0°.
Describe the structure of and the process of light travelling via an optical fibre
● A core surrounded by cladding of lower refractive index (1).
● Light enters, is slightly refracted at the start, is totally internally reflected when the angle of incidence ≥ critical angle (1).
What are lasers sources of?
Coherent, monochromatic light.
What is monochromatic light?
Light of a single frequency/wavelength.
What wavelength diffract more and why?
Longer wavelengths because they have a lower frequency so less energy. The more energy a wave has, the greater it’s tendency to travel in a straight line.
p = mv
Describe what appears on the screen under single slit diffraction?
A diffraction pattern of alternating light and dark fringes.
The central fringe is brighter and double in size.
The fringes get dimmer as you move away from the centre
What will always be in the centre of a diffraction pattern and why ?
The maximum bright fringe.
As the centre is symmetric to all the slits so light from each slit will travel a whole number of waves to reach it, arrive in phase and constructively interfere.
