P14 Light Flashcards
what are convex lenses?
they are thicker at the centre than they are at the edges
what is the symbol for convex lenses?
a line with two arrows pointing away from the centre
what do lenses do?
refract light
the light ray bends towards the normal when it enters the lens and away from the normal when it leaves the lens
what are the facts about when parallel rays of light pass through a convex lens?
the central ray passes through the lens without being refracted (it is directly along the normal)
all other rays refract and are focused on a point
what is the principle axis?
the line through the centre of the lens (perpendicular bisector)
what is the principle focus (F)?
where all the parallel rays meet once they pass through the convex lens
what is the focal length?
the distance from the centre of the lens to the principle focus (F)
what is the image like when the object is at least 2 focal lengths away from the lens? (for a convex lens)
the image is:
diminished
inverted
real
what happens with a real image?
the rays ACTUALLY meet at a point
if a screen was placed where the image is, you would see it
what is the image like when the object is between 1 and 2 focal lengths away from the lens?
the image is:
inverted
magnified
real
what is the image like when the object is less than 1 focal length from the convex lens?
the image is:
magnified
erect
virtual
why are dotted lines used when there is a virtual image?
they do not represent the actual path of the rays
how can you tell that an image is virtual?
the rays do not actually meet, they only appear to meet
when does a convex lens produce a virtual image?
when it is used as a magnifying glass
what are the units of magnification?
magnification has no units as it is a ratio
what is a concave lens?
a lens thicker at the edges than at the centre
what is the symbol of a concave lens?
a line with arrows pointing in towards the centre
what do concave lenses do to parallel rays of light?
they make them spread out (diverge)
what is the principle focus of a concave lens?
the point behind the lens where diverging light rays meet if they were to be extended
what are the key properties of an image produced by a concave lens?
the image is:
diminished
right way up (erect)
virtual
what is a specular reflection?
when the light rays reflect in a single direction
this takes place on smooth surfaces
what is a specular reflection?
when the light rays reflect in a single direction
this takes place on smooth surfaces and produces an image
what is a diffuse reflection?
when the light rays are scattered
this takes place on rough surfaces and does not produce an image
what is white light made up of?
a mixture of all different colours
what are the colours of the visible light spectrum?
red
orange
yellow
green
blue
indigo
violet
what does the colour of an object depend on?
it depends on which wavelengths of light are reflected, transmitted or absorbed
how do coloured filters work?
they absorb specific wavelengths and transmitting other wavelengths
how can you describe objects which transmit light?
transparent or translucent
what do translucent objects do to light rays?
they scatter the light rays so you cannot see through it clearly
what are opaque objects?
objects that you cannot see through
why do white objects appear white?
they reflect all the wavelengths of light equally
why do black objects appear black?
they absorb all of the wavelengths of light
why do objects have different colours?
they absorb all other wavelengths of the light apart from the colour of the object, which is reflected
