Lenses Flashcards
How can you tell if the light is slowing down?
If when it’s refracted, it bends towards the normal
How can you tell if the light is speeding up?
If when it’s refracted, it bends away from the normal
What is the normal?
A line that is perpendicular to the interface of the medium
What is the refractive index?
A measure of how much the material slows down light
What is the formula for the refractive index of a material?
n = c/v
refractive index = speed of light/ the speed of light in the material
What does Snell’s law state about the refractive index of a material?
When light travels through an optically denser medium it is refracted toward the normal so
n1sin(angle of incidence) = n2sin(the refracted angle)
What is the critical angle?
When light travels from a denser to a less dense medium,
there is an angle of incidence that causes the light to be refracted at 90 (on the boundary of the medium
What is the formula used when the light goes from a material boundary to air?
sinC(critical angle) = 1/n (this is because n of air is 1 and the sin90 is 1)
What are lenses?
Something that changes the direction of light using refraction
What are converging lenses?
Lenses that bulge outwards and cause light to converge at the principal focus point
In converging lenses what happens to rays that are parallel to the principal axes?
They are refracted until they converge at the principal focus point.
What is the focal length?
Distance between the lens and the focal plane
Where parallel rays ( from infinity) are brought to a point.
What are diverging lenses?
They cave inwards. The principal focus point is before the lens. So they cause the rays to spread out
What is a real image?
Light rays that are actually there and can be captured on screen.
Light rays converge to a point where the image can be found.
How is a real image formed?
When light rays from an object are made to pass through another point in space
What are virtual images?
Light rays that aren’t actually there so cannot be captured on a screen
How are virtual images formed?
When light rays on an object appear to have come from a different point in space
What is the relationship between converging lenses, real images, virtual images, and the distance from the focal point?
If the object is closer to the lens than the focal point is, then it will form a virtual image
If the object is further away from the lense than the focal point then it will form a real image.
What type of image will a diverging lens form?
Always a virtual image
What is the formula that links the image length(v), the object length(u), and the focal length(f)?
1/f (Power of lens)= 1/u +1/v
Only works for thin lenses tho xD
What is the formula for the power of a lens?
P = 1/focal length
What are the units for the power of a lens?
Dioptres (D)
What is the formula for magnification?
magnification = image height/ object height?
m = v/u
How to find the critical angle between 2 media?
SinC = n²÷n¹
