LIGHT Flashcards
(30 cards)
How fast can light travel
Light travels 300,000 km per second in space taking almost 10 minutes to reach earth. Light consists of particles called photons that travel as a wave.
What are the sources of light
The sources of light can be luminous objects and substances that emit light on their own. A type of source is incandescent which is an object or substance that emits light because they are hot. eg) lightbulbs, flames,sun.
Non-incandescent is a substance or object that emits light without getting hot. eg) LED lights, some deep sea fish, glow-worms.
Living things that emit light without heat are referred to as bioluminescent.
How can we see objects?
most things that you see are non-luminous( they do not emit their own light) however we are able to see these objects because light from luminous objects is reflected from them. Eg) the moon is not a luminous object, its surface simply reflects light from the sun.
Seeing light
light can be seen when looking at a luminous object or when looking at an object that reflects light into your eyes. Light is not normally visible between its source and any surface that it strikes. You can only see a beam of light if there are particles in the air to scatter light back to your eye.
When light meets a substance it can be…
Reflected- when light bounces of the object.
Absorbed- when light is taken into the object.
Transmitted- when light passes through the object.
Types of objects
Transparent- Materials like glass that allows light to pass through.
Opaque- Objects that absorb or reflect all light striking through.
Translucent- only allows some light to pass through the object, unable to see through clearly.
The electromagnetic spectrum
Visible light is just one part of a ‘family’ of forms of energy known as electromagnetic radiation emitted by the Sun and other stars.
Along with visible light the electromagnetic spectrum consists of radio waves microwaves, infra-red radiation ultraviolet radiation x-rays and gamma rays. All types of electromagnetic radiation can be produced artificially here on Earth.
Visible light spectrum
In 1666, the English scientist Isaac Newton passed a narrow beam of light through a glass triangular prism. Newton classified the colours of the spectrum as red, orange, yellow, green, blue, indigo & violet.
The splitting of white light into the colours that make up white light is called dispersion.
Dispersion of white light
Each colour from the original beam of light has its own particular wavelength & each wavelength is slowed differently by the glass.
The amount of refraction increases as the wavelength of light decreases.
Shorter wavelengths of light (violet & blue) are slowed more and consequently experience more bending than longer wavelengths (orange & red).
Light waves
Light travel via waves known as transverse waves. This is when the waves of energy move up and down and travel through space. Radio waves have larger wavelengths and can pass through a brick wall and that is why you can tune into a radio inside your home.
Rainbows
rainbows are formed because rain droplets act as prisms. The droplets disperse white light into the seven colours of the spectrum.
The sun behind you shines on the rain droplets causing the rainbow.
Rays
Light is especially important to us because of its ability to form images.
The reflection of light allows you to see images in mirrors. When you take a photo, the image is created when light is bent by a lens. Light travels in straight lines.
The lines that are used to show the path of light are called rays. A beam of light is a stream of light rays.
Reflection
When you look in a mirror you see an image of yourself.
If the mirror is a plane or flat mirror, the image will be very much like the real you.
If the mirror is curved, the image might be quite strange.
Reflection depends on how smooth a surface is
Law or reflection
Whenever light is reflected (angle of reflection)from a smooth, flat surface, it bounces away from the surface at the same angle from which it came (angle of incidence).
Law of reflection rule
Angle of Incidence = Angle of Reflection
Reflection of light from a mirror
The normal: a dotted, imaginary line drawn at 90° (perpendicular) to the mirror.
Incident ray: incoming light.
Reflected ray: light leaving the mirror.
Angle of incidence: angle between the incident ray and the normal.
Angle of reflection: angle between the reflected ray and normal.
Plane mirrors
When we look in a plane (flat) mirror:
- The image is not real-it is a virtual image (it cannot be captured on paper or a screen).
- The image is the same distance behind the mirror as the real person in front of the mirror.
- The image is the same size as the original, but it is laterally inverted (reversed sideways).
Mirror images
When looking at a mirror we know that the object is NOT behind the mirror. This is termed virtual image
Spherical mirrors
Spherical mirrors are mirrors having curved surfaces that are painted on one of the sides.
Spherical mirrors in which inward surfaces are painted are known as convex mirrors.
Spherical mirrors in which outward surfaces are painted are considered concave mirrors.
Convex mirrors
The convex mirror allows the observer to see a larger field of view.
They are used to see traffic around a corner, for car mirrors and in shops to see people in the aisles
Concave mirrors
The concave mirrors allows the observer to see close up .They can also concentrate light for uses such as a light house, telescope or heating water.
What is refraction
Refraction is the bending of light as it passes, at an angle, from one transparent material into another.
The light bends because it changes speed.
Light travels at different speeds through different substances.
The differences in its speed result in different amounts of bending, or refraction, as light passes from one substance into another.
The more dense the material the more the light bends towards the middle of the object.
What are the functions of each structure of the eye?
Pupil- allows light into the eye.
Iris- Controls the size of the pupil.
Lens- Focuses light onto the retina
Retina- Detects light using cells called photoreceptors
Optic nerve- Receives signals from the retina and sends them to the brain.
Sclera- Protects the eye and helps maintain its shape.
Choroid- Contains blood vessels, which brings nutrients to the eye.
Cornea- Protects the front of the eye.
Vitreous humor- Helps the eye maintain its shape
Aqueous humor- Brings nutrients to the cornea and lens, which lack blood vessels.
What are the types of photoreceptors?
Photoreceptors are located on the back of the eye. The two types are rods and cones. Rods respond slowly and operate in dim light, and cannot recognise colour. There are more rods in the eye than cones. Cones are responsible for colour vision and can recognise red blue and green light.
