Light Flashcards
What is light?
Form of energy which comes mainly from the sun.
Some objects, like the sun produce their own light, they are known as luminous sources.
Other objects like the moon only reflect light and do not produce their own, they are non-luminous.
What does Opaque, translucent and transparent mean?
Opaque - does not let light pass through
Translucent - lets some light through
Transparent - lets all light pass through
What is it called when two or more rays (light moving in straight lines) are together?
Beam of light
What are the three types of beams of light?
Parallel beam - rays alongside each other
Convergent beam - rays going into each other
Divergent beam - rays going away from each other
How fast does light travel?
300 000 000 m/s
What are shadows?
Formed when light strikes an opaque object.
The light cannot travel through the object and does not go around it.
This means that there is an area with little or no light behind the object and also tells us that light travels in straight lines.
What is regular and diffuse reflection?
Diffuse is when a beam of light hits an object it usually reflects in all different directions (A rough surface).
Regular is when you have a very smooth surface the rays all go in the same direction.
What can we say about the angle of incidence and the angle of reflection?
Law of reflection states that the angle of reflection is equal to the angle of incidence
What is lateral inversion?
When an object is reflected in a mirror, left is right and right is left on the image.
Problems with it can be that it can confuse the brain and co-ordination.
What is a virtual image?
Image only appears to be behind the mirror - it isn’t physically there
What is refraction?
Light changing speed and direction when it passes from one material to another
What happens when light travels from a less dense to a more dense material i.e. air into glass
Light is refracted (bent) towards the normal.
Glass into air meaning light bends away from the normal (more dense into less dense)
Why does refraction happen?
Light travels faster in less dense materials and slower in more dense.
Light won’t change direction if it hits glass at 90 degrees (angle of incidence is 0 degrees) but it will still change speed and slow down.
What is the critical angle?
When the angle of refraction is 90 degrees.
If the angle of incidence in glass is greater than the critical angle then the refracted ray disappears and all the light is reflected inside the glass, this is total internal reflection and only happens when light travels from a more dense to a less dense material.
How does Total Internal reflection happen?
If the angle of incidence is bigger than the critical angle.
Critical angle of glass is 42 degrees.
What can total internal reflection be used for?
TIR prisms and Optical fibres
What is dispersion?
If we allow white light e.g. sunlight to pass through a prism we can see that white light is split into seven different colours and this band of colours is called a spectrum.
Why does dispersion happen?
Some colours slow down more than others, violet slows down the most and refracts the most, red refracts the least and refracts through the smallest angle.
Order of the electromagnetic spectrum
Radio waves, micro waves, IR, Visible, UV, X-rays, gamma rays
Properties of electromagnetic spectrum
They are all transverse waves.
Can all travel through a vacuum and at the same speed in a vacuum.
As it goes from radio to gamma the wavelength decreases and frequency increases.
What are the two types of lenses?
Converging/convex - rays go toward each other.
Diverging/concave - rays go away from each other.
What is the principal focus (focal point)?
The point on the principal axis to which all rays which are parallel to the principal axis will converge after passing through the lens.
What is the focal length?
Distance from the principal focus to the centre of the lens.
Function of each part of the eye
Lens - changes shape to allow focusing on the retina.
Retina - contains light sensitive cells at back of eyeball to collect info (sense light).
Fovea - area of eye used for sharp central vision.
Optical nerve - transports electrical signals to brain.
Pupil - allows & controls the light into the eye
