Paper 2 Lenses/light Flashcards
What are the two major types of lens
Concave (or diverging)
Convex (or converging)
What is a converging lens
The lens is thicker at the centre than it is at the edges
It makes parallel rays of light converge to a single point, F (this point is the principle focus of the lens)
What is the focal length
The distance between the focus point and the centre of the lens
What is a diverging lens
The lens in thinner at its centre than at its edges
Makes parallel rays of light diverge as though from a single point, F
Magnification =
Image height/ object height
If the image is larger than the object the magnification is…
Greater than 1
If the image is smaller than the object the magnification is…
Less than 1
What are ray diagrams used for
Used to explain the formation of the image
Two rays of light which originate from a single point on the object should be drawn
The image produced from a convex lens can be
Diminished/magnified
Inverted/upright
Real/virtual
What happens in ray diagrams for concave lenses
The ray parallel to the principal axis will reflect as if it passes through the focal point on the objects side
What is white light made up of
All the wavelengths in the visible part of the spectrum
How are the colours of the spectrum separated
The different wavelengths experience different changes in speed as they enter and leave the glass so bend (refract) by different amounts, so the colours are separated
Cyan is made by mixing…
Green and blue
Magenta is made by mixing…
Red and blue
Yellow is made by mixing…
Red and green
What do coloured filters do
They only allow a particular small range of wavelengths to pass through
A red filter…
Allows red light through but absorbs green and blue
A yellow filter…
Allows red and green light to pass through but absorbs blue light
How are light rays reflected by flat foil
Reflected in single direction (specular reflection)
How are light rays reflected by crumpled foil
It was scattered called diffuse reflection
Primary colours only transmit…
Their own colour
Secondary colours only transmit…
The colours they are made up of e.g magenta only transmits blue and red
What happens when visible light waves hit opaque objects
They absorb some wavelengths of light and reflect others
Why does a red book appear to be red
Because the wavelengths corresponding to the red part of the visible spectrum are most strongly reflected. The other wavelengths of light are absorbed
What happens if red light is shone on blue shorts
They appear black because the red light is absorbed
