Prisms Flashcards
Prism?
Two flat polished refracting surfaces inclined at an angle relative to each other
Prisms have an apex, apex angle, base
What does dispersion mean?
When a beam of light passes through a prism it splits into a spectrum of colours
Why is blue light refracted more than red light?
Blue is shorter in wavelength
Dispersion can not occur for what light?
Monochromatic light
Where does the light move towards?
The base
Where does the image move towards
The apex
What is the angle of deviation dependant on
-refractive index of prism
-angle of incidence
-apex angle
What is the angle of deviation
The light ray is deviated towards the base of the prism, this net change in direction is called the angle of deviation
What is the minimum angle of deviation
It occurs when the light passes symmetrically through the prism, the angle of incidence equals the angle of emergence
What are the unit for prisms
Prism dioptre
Centrad
Where does displacement happen for a prism diaptore
Over a flat surface
Displacement for centrad?
Over an arc
Prism power?
How much the prism causes the light to change direction
Prism dioptre formula
P= shift in cm/ distance in m
Prisms at more powerful in what position?
Prentice position than in the position of minimum deviation
Prentice position?
90 degrees to the interface and straight
Using mostly thin prisms leads to?
Good quality images, this is shifted but not deformed because of the small apical angle of the prism
Small apical angle= good image quality
What is a Lens
A lens is an optical device used to alter the vergence of light passing through it
What is the formula for vergence power or surface power
F = n2-n1 /r
If F IS POSITIVE than it’s converging- moving towards axis
IF F IS NEGATIVE THAN it’s diverging
F IS MEASURED IN D (diopters) not that same as prims diopters
How do you identify a convex lens
It’s thicker in the centre and thinner edge
Other forms of convex lenses are biconves lens, plano convex and convex meniscus which all have a positive vergence power
How to you identify concave lenses
Thin centre and thicker edge
Examples are biconcave lens, plano concave and concave meniscus which all have a negative vergence power
Thins Lens?
Thickness can be ignored so bending of light rays takes place approx at the centre of Lens
How many focal points do lens have
2
How many focal points do mirrors have
1
For a convex lens where is F2 located
Behind the lens
For a convex lens, where is F1 located
Infront of the lens
For concave lens where is F2 located
Infront of the lens- this is where parallel rays cross
For concave Lens where is F1 located
Behind the lens so rays from F1 are deflected into parallel rays
What is the vergence power related to
The focal point
- the shorter the focal length the more powerful the lens
The vergence power is related to the focal point
What is the formula to calculate the focal length?
F= 1/ f(in metres)
