Light Flashcards
What is light?
A form of energy.
What are luminous objects?
Give an example of something that is and isn’t luminous.
Produces its own light,
The son is luminous, but the moon isn’t, as it reflects the sun’s light and doesn’t produce its own.
What do the following terms mean:
Opaque?
Translucent?
Transparent?
Light cannot pass
Some light can pass
Light can pass
What is a ray?
A straight line which light moves in.
What is a beam?
Two or more rays of light together.
What are the 3 types of beam?
Parallel beam (rays parallel)
Convergent beam (rays point inwards)
Divergent beam (rays point outwards)
What is the speed of light?
300,000,000m/s or 3 x 10^8m/s
What are shadows?
What can they tell us about light.
Formed when light strikes an opaque object. Light cannot pass through or go around, forming an area with little to no light in it.
Tells us that light travels in a straight line.
What is regular reflection?
Light strikes a smooth surface and all rays are reflected in the same direction.
What is diffuse reflection?
When light hits a ‘rough’ object and is reflected in all directions.
What is lateral inversion in a mirror?
When an object is reflected in a mirror, left is right and right is left on the image.
What is refraction?
When light changes it’s speed and direction when it passes from one material to another.
What is the relationship between the angle of incidence and the angle of reflection in a mirror?
They are equal.
What is a virtual image?
Cannot be formed on a screen, e.g. mirrors.
What is the relationship between the distance between the object and the mirror and the distance between the mirror and the image behind it?
They are equal.
What is the relationship between the angle of incidence and the angle of refraction?
Angle of refraction is less than angel of incidence.
Is light refracted towards or away from the normal when it travels from a less to more dense material?
Towards the normal.
Is light refracted towards or away from the normal when it travels from a more to less dense material?
Away from the normal.
What is the relationship between the direction of the incident ray and the emergent ray in a glass block?
They are parallel.
What happens to the speed of light when it enters a glass block?
Decreases
What happens to the speed of light when it leaves a glass block?
Increases
What does a wavefront diagram look like?
How does it interact with a glass block.
Light represented as a series of parallel lines (wavefronts) lined up.
When it reaches a glass block, one end of the wavefront enters the glass block before the other. As this end slows down more, it causes the wavefront to change direction. When the beam leaves the glass block, the other end leaves before the first, causing it to change back again.
What is internal reflection?
When light passes from glass into air, there is a refracted ray into the air and a reflected ray back into the glass.
What is the critical angle?
As the angle of incidence increases, the angle of refraction also increases until a certain angle of incidence called the critical angle, represented as c, is reached. This makes the angle of refraction 90, and it fails to emerge into the air.
In angles of incidence above c the refracted ray disappears and all light is reflected inside the glass. This is called Total internal reflection. Emphasis on total.
What are some uses of total internal reflection?
Periscopes, binoculars, fibre optic cables.
What is dispersion?
When white light is split into seven different colours when passed through a triangular prism.
This band of colours is called a spectrum.
Why does dispersion occur?
White light is made of seven different colours of light. Each colour of light is slowed by different amounts in the glass and so is refracted by different angles, thus splitting the beam of light.
What are electromagnetic waves?
Energy that travels at the speed of light in a vacuum.
aka different types of light
What are the 7 types of electromagnetic waves?
List them in order of short wavelength to long wavelength.
Gamma (Good)
X- rays (Xmen)
Ultraviolet (understand)
Visible (very)
Infrared (important)
Microwaves (mission)
Radio waves (reports)
What do all electromagnetic waves have in common?
Same speed in a vacuum
All transverse
All reflected and refracted
What are some uses of gamma waves?
What is their effect on humans?
Cancer treatment and sterilising medical equipment
Causes cancer (highly ionising)
What are some uses of X rays?
What is their effect on humans?
X-ray imaging - luggage, broken bones, cancer diagnosis
Causes cancer
What are some uses of UV waves?
What is their effect on humans?
Kill bacteria, detecting forged bank notes
Skin Cancer
What are some uses of visible light?
What is their effect on humans?
Photosynthesis and photography
Can damage retina
What are some uses of infrared waves?
What is their effect on humans?
Toasters/grills, heating elements, night vision cameras.
Burns skin.
What are some uses of microwaves?
What is their effect on humans?
Microwave oven, set Navs, communication
Easily absorbed by water
What are some uses of radio waves?
What is their effect on humans?
TV/Radio signals and CB radio comms
Damages hearing
What is a concave lens?
Lens curved inwards, diverges light
What is a convex lens?
Lens curved outwards, converges light
What is the principle focus?
The point on the principal axis (which all rays are parallel to) will converge after passing through the lens.
Represented by F
What is the focal length?
The distance between the optical centre and principal focus.
Represented by f
What is the relationship between focal length and lens thickness?
The thicker the lens, the shorter the focal length.
What is long sightedness?
Close objects are blurred, as eyeball is too short and focus is behind the retina.
Fixed with convex lens.
What is short sightedness?
You.
Distant objects are blurred as the eyeball is too long and the focus is in front of the retina.
Fixed with a concave lens,
How do you draw ray diagrams?
Draw the lens and principal axis (straight line that goes through the optical centre) and mark on the points F and 2F
Draw the object as an upright arrow on the principal axis.
Then, draw 2 rays coming off the object. A ray parallel to the principle axis which is refracted, passing through the principal focus or a ray that passes through the principal focus that refracts parallel to the principal axis (basically opposite of the last one) and a ray which passes through the optical centre of the lens which continues without changing direction
Where will the image be on a ray digram?
Where the two rays of light meet.
What does a real and virtual image look like on a ray digram?
Real image is in front of the lens.
Virtual image is behind the lens.
What does an inverted and upright image look like on a ray digram?
Inverted image is below principle axis
Upright image is above principal axis
What does a magnified, diminished and same size image look like on a ray digram?
Magnified image arrow longer than object arrow
Diminished image arrow shorter than object arrow
Same size image arrow same size as object arrow
