Light Flashcards
Define the angle of incidence
The angle between the normal and the incident ray
Define the angle of reflection
The angle between the normal and the reflected ray
What is refraction?
Refraction is the change in direction of a beam of light as it travels from one material to another due to a change in speed of light in the different materials.
Define angle of refraction
Is the angle between the normal and the refracted ray.
What is dispersion?
Different colours of light travel at different speeds in glass. This means the different colours bend (refract) at different angles. This effect is called dispersion. When light is passed through a prism a spectrum of colours can be seen of red orange yellow green blue indigo and violet (rainbow).
Define dispersion
The splitting of white light into its component colours.
Define critical angle
The angle of incidence in the medium resulting in an angle of refraction of 90° in air.
Define total internal reflection
What occurs when light is travelling in an optically dense material towards a boundary with an optically rare material, and the angle of incidence at the boundary is greater than the critical angle.
What is the critical angle
The angle in which the internally reflected light ray becomes stronger with the refracted ray being at 90°
What is total internal reflection
All the light being reflected back into the glass.
What are optical fibres
Lengths of solid glass core with an outer plastic sheath. Provided the fibre is not bent too tightly light will strike the core cladding boundary at at an angle greater than the critical angle and be totally internally reflected
What are advantages of optical fibres?
They can carry much more information than a copper cable of the same diameter
Define converging (convex) lens
A lens that is thickest at its centre and least thick at its edges
Define diverging (concave) lens
A lens that is thickest at its edges and is least thickest at its centre.
Define principle axis
A straight line joining the principle foci and passing through the optical centre of a converging (convex) lens
Define principle focus
A point on the principle axis of a converging lens through which rays of light parallel to the principle axis pass after refraction in the lens.
Define focal length
The distance between the optical centre or a lens and the principal focus.
Define the main feature of a converging lens
Rays of light parallel to the principal axis of a converging lens all converge at the principle focus on the opposite side of the lens.
Define the main feature of a diverging lens
Rays of light parallel to the principal axis of a diverging lens all appear to diverge from the principal focus after refraction in the lens.
How are images always described when in a diverging lens
Erect
Virtual
Smaller than the object
Define myopia (short sight)
A defect of the eye in which distant objects appear blurred because the images are focused in front of the retina rather than on it.
What lens is used to fix the shortsighted defect?
Diverging lens (concave)
Define hypermetropia (long sight)
A defect in which near objects appear blurred because the images are focused behind the retina rather than on it.
What lens is used to correct longsightedness?
Converging (convex) lens
