P14 - Light✔️ Flashcards
Effect of a convex lens?
Causes rays of light parallel to the axis to be brought together (converge) at the principal focus
Shape of a convex lens?
Bulges outwards
Shape of a concave lens?
Caves inwards
Effect of a concave lens?
Causes parallel rays of light to spread out (diverge)
What is the axis of a lens?
A line passing through the middle of the lens
What is the principal focus of a convex lens?
Where rays hitting the lens parallel to the axis all meet
What is the principal focus of a concave lens?
point where rays hitting the lens paralle to the axis appear to all come from - can trace them back until they all appear to meet up at a point behind the lens
What is the focal length?
Distance from the centre of the lens to the principal focus
Give the three rules for refraction of convex lens?
- incident ray parallel to axis refracts through lens - passes through principal focus on other side
- incident ray passing through principal focus refracts through lens and travels parallel to the axis
- incident ray passing through centre of lens carries on in same direction
Give the three rules for refraction of concave lens?
- incident ray parallel to the axis reflects through lens and travels in line with principal focus
- incident ray passing through lens towards principal focus refracts through lens and travels parallel to axis
- incident ray passing through centre of the lens carries on in the same direction
What happens to an incident ray passing through centre of a concave lens?
incident ray passing through centre of the concave lens carries on in the same direction
What happens to an incident ray passing through centre of a convex lens?
incident ray passing through centre of the convex lens carries on in the same direction
Define a real image?
Where light from an object comes together to form an image on a screen - eg the image formed on the eyes retina
Define a virtual image?
Where the rays are diverging, so light from the object appears to be coming from a completely different place - eg when looking in a mirror you see a virtual image of your face because your face appears to be behind the mirror
How can virtual images be usefull?
Used in magnifying lens - can make an object look bigger then it actually is
Give the name of the lens which always creates virtual images?
Concave lens - the image is always the right way up, smaller than the object and on the same side of the lens as the object
Equation for magnification?
Magnification = image height / object height
Explain why light appears white?
Visbile light is made up of a range of colours with varying wavelengths (and frequencies) ranging from violets down at 400nm up to reds at 700nm - when all the colours are put together it creates white light
What are opaque objects?
Objects that do not transmit light - when visible light waves hit them, they absorb some wavelengths of light and reflect others
What does the colour of opaque objects depend on?
Depends on which wavelengths of light are most strongly reflected - if the opaque objects is not a primary colour, they may be reflecting either the wavelength of light corresponding to that colour - or the wavelength of the primary colours that mix together to make that colour
What are white objects?
Objects that reflect all of the wavelengths of visible light
what are black objects?
Objects that absorb all wavelengths of visible light
Effects of transparent and translucent objects on light?
Transmit light - not all the light that hits the surface of the object is absorbed or reflected - some can pass through - the colour of the object is related to the wavelength of light transmitted and reflected by it
What are colour filters used for?
Used to filter out different wavelengths of light - so that only certain colours (wavelengths) are transmitted - the rest are absorbed
What do primary colour filters do?
Only transmits that colour - eg if white light is shone at blue colour filter, only blue light will be let through - rest of the light will be absorbed - if object was red it would appear black when viewed through the filter - as all the light reflected by the object would be asborbed by the filter
What do filters that aren’t primary colours do?
Let both the wavelengths of light for that colour - and the wavelengths of the primary colours that can be added to make that colour
Difference between transparent and translucent objects?
Transparent emits all the light that enters the object, no light is absorbed - translucent objects let light through but the light is refracted and scattered
What does the colour of an object depend on?
Depends on the pigment of the surface material and the wavlengths of light that the pigments absorb
