Light2 Flashcards
A Spectrum is
A band of colours that is formed when light is dispersed into its component colours
Name the colours in decreasing wavelength
Red Orange Yellow Green Blue Indigo Violet
Def a Lens
A piece of any transparent substance that has at least one curved surface
Def the Optical Centre
Is the centre of the lens through which light passes without changing direction
Def principal axis
Is the straight line passing through the centres of curvature of a lens
Def principal focus
Is the POINT to which rays of light travelling parallel to the principal axis converge,
or the point from which they appear to diverge,
After having been refracted by a lens
Define Focal Length
Is the distance from the optical centre to the principal focus
Def focal plane
Is the line drawn perpendiclarly to the axis at the principal focus
Define Magnification
Is the ratio of the size of the image to the size pf the object
Name the 2 types of lenses
Converging
Diverging
Name 3 different converging lenses
Biconvex
Plano-convex
Concavo-convex
Name 3 types of diverging lenses
Biconcave
Plano-concave
Convexo-concave
Name 5 differences between Real and Virtual immages
REAL
Light rays pass through the immage
Inverted
Can be projected onto a screen
Is on the opposit side of the lens to the object
Draw a ray diagram where the object is on F2. Convex lens
A
Give the calculation to work out magnification
Size of image / size of object
Distance of immage / distance of object
Compare the eye to a camera
10 comparasons
Eyelid/ shutter. Iris/ diaphrame. Pupil/ appeture. Lens/ lens. Retina./film.
Black melanin choroid/ black of camera
Name the two main defects to your eyes associated to lenses
Short-sightedness
Long-sightedness
Describe what is wrong with the eye’s lens when a person is long-sighted
Person can see objects far away,but not close-by
The lens is too flat (it has lost its elasticity and does not return to its normal rounded shape. Normally due to old age).
F1 falls behind retina and the image cannot be focussed on the retina
How do one rectify far-sightedness
By adding an extra converging lens (using glasses or contact lenses)
The added lens helps to converge the rays a bit more and the eye can then focus the image on the retina
What is wrong with the eye’s lens in short-sighted patients.
The lens is too bulbous (cilliary muscle does not pull it flat enough). F1 is too short
The patient can see nearby objects, but far away objects cannot be focussed on the retina, because the image is formed in front of the retina
How do they fix short-sightedness
By adding an extra diverging lens
The total focal length gets lengthened
The eye can now accompdate and
Define dispersion
It is the splitting up of light into its component colours by refraction.
It occurs because the refractive index of glass is different for each colour