P14-Light Flashcards
What happens when plane waves reflect from a flat barrier?
The reflected waves are at the same angle to the barrier as the incident waves
What happens when each point on the wave front teaches the barrier?
It creates a wavelet moving away from the barrier, the wavelet lines up with the previous reflected wavelets to form a reflected wave front moving away
All parts of a wavefront move at the same speed. What does this mean?
the reflected wavefront is at the same angle to the barrier as the incident wavefront
In reflection, the reflected and incident waves have the same what?
Frequency, speed and wavelength
What do light rays show?
The direction that light waves are moving in
The line perpendicular to the mirror is called the what?
the Normal
What is the angle of incidence?
the angle between the incident ray and the normal
What is the angle of reflection?
angle between reflected ray and the normal
What is the image formed by a plane mirror?
virtual
When is a virtual image formed?
When light rays appear to come from after they have been reflected or refracted
What is a real image
An image that can be seen on a screen
what is a virtual image?
- same way up as the object
2. laterally inverted (back to front not upside down)
What is specular reflection?
Diffusion from a smooth surface because parallel light waves are reflected in a single direction
What can a virtual image not do?
be projected onto a screen like the movie images you see at a cinema
Why may a real image be described as something seen on a screen?
A real image is formed by focusing light rays onto the screen
What is reflection from a rough surface called why?
diffuse reflection- light is scattered in different directions
Each lens changes the direction of light passing through it. What is this change of direction called?
refraction
What is refraction?
The change in direction of waves across a boundary from one medium to another
When do light waves refract?
When they travel across a boundary between air and a transparent medium.
Why does light refract across a boundary between air and a transparent medium.?
This is because speed of light changes at this type of boundary
What does light do when it travels from air to glass?
Bends towards the normal
What does light do when it travels from glass to air?
Bends away from the normal
What does light bend away from the normal when it travels from glass to air
Light travels more slowly in glass than air and glass is more optically dense than air
What happens when light enters a more dense medium?
Refracted towards normal
What happens when light enters a less dense medium?
Refracted away from medium
How do colour filters work?
They absorb certain wavelengths and transmit others e.g. white light at red filter inky red light emitted because it absorbs all parts of white spectrum
What are the primary colours of light? And why are they the primary colours?
Red, green and blue and because they can be mixed to produce any other colour of light
What does the colour and surface of an opaque object depend on?
The chemicals (pigments) in the surface materials
What does colour also depend upon?
The range of wavelengths in the incident light
What does a white surface not have ?
Pigments
What are transparent objects?
Objects that transmit all the incident light that hit object, none is absorbed
What are translucent objects?
Objects that let light pass through but is scattered or refracted
Why do translucent objects let light pass through but is scattered or refracted
Material of object has lots of internal boundaries that change the direction of the light waves
What is another word for convex lens
converging
What is a convex lens?
Makes parallel rays converge to a focus
What is the point called where parallel rays are focused to?
Principal focus
What is a converging lens used for?
Magnifying glass e.g. distant objects in a camera
What is a concave lens used for?
Makes parallel rays spread out
Whats another word for concave?
diverging
What is a diverging lens used for?
Correcting short sight
What is the distance from the centre of the lens to the principle focus called?
Focal length
What happens if the image is bigger than the object?
The magnification is bigger than 1
What happens if the image is smaller than the object?
The magnification is less than 1
What image is formed by a convex lens?
A real image if the object is further away than the principal focus
What image is formed by a convex lens?
A virtual image if object is nearer the principal focus
The magnification produced by a lens is what formula?
image height over object height
