P14 Light Flashcards
what is diffraction
spreading out of waves in a circular motion when they come to a hole in a boundary
what is a virtual image
an image formed at a place where light rays appear to come from after they have been reflected or refracted
what is a real image
an image that can be projected onto a screen as it is formed by focusing light rays onto the screen
what is specular reflection
reflection from a smooth surface- parallel rays are reflected in a single direction (not scattered)
what is diffuse reflection
reflection from a rough surface- light is scattered in different directions
what is refraction and why does it happen
the change of direction of light and sound waves- happens because they change speed as they cross the boundary between 2 substances with different densities causing them to change direction
when does refraction not occur
when light rays hit the normal straight (90) as all of the wave hits the normal at the same time
what happens when a wave crosses a boundary into a substance of a higher density
starts to go slower so it bends towards the normal decreasing the angle of refraction
what happens when a wave crosses a boundary into a substance of a lower density
wave travels faster so it bends away from normal
how is a critical angle formed
when the angle of incidence gets so big that it refracts at 90 to the normal and angle of i becomes critical angle
what is total internal reflection
when the angle of incidence is bigger than the critical angle so the ray is reflected
what causes a light wave to be refracted
when they travel across a boundary between air and a transparent medium or between 2 transparent media as speed of light changes
what happens in optical fibres
total internal reflection
how do colour filters work
by absorbing certain wavelengths and transmitting other wavelenghts eg when white light is directed at a red filter, the filter transmits only red light as it absorbs all other parts of the white light spectrum
why does white surface reflect light of any wavelength
has no pigments which are chemicals in the surface materials
why can you see clearly through a transparent object
they transmit all the incident light that enters the object that then travels through the object. No light is absorbed at the surface
why can you see light but not images through tarnslucent objects
the light is scattered or refracted because the material has lots of internal boundaries that changes the rray direction frequently
why can’t you see through an opaque object
it absorbs all the light that reaches it . No light travels all the way through it. It is either; reflected, scattered at the surface or absorbed by the object
what is the magnification equation
image height/ object height
how does a convex lens (converging lens) work
makes parallel rays converge to a focus ( pricipal focus/ focal point) of the lens. Used as a magnifying glass an in a camera to form a clear image of a distant object
how does a concave lens (diverging lens) work
makes parallel rays diverge (spread out ). The rays appear to come from the principal focus of the lens. Used to correct short sight
what is the focal length of the lens
the distance from the centre of the lens to the principal focus
when is a real image formed by a convex lens
when the object is further away than the principal focus
when is a virtual image formed by a convex lens
when the object is nearer than the principal focus
what lens is in a camera
convex- forms a real image of an object
what lens is in a magnifying glass
convex- forms a virtual image of an object
