Light is a form of energy. It is a form ofelectromagnetic radiation.
Is objects that emit light. Release light together with a large amountof heat. Examples : Sun, stars, fire and candle flames.
Is objects that do not emit light. Can only be seen if they are reflecting light from aluminous source. The moon is a non-luminous body because the moonget light from sunlight that is reflected.
Light leaves the surface of a luminous object in alldirections but if some of the light is made to passthrough a hole it can be seen to travel in straightlines. Ray is smaller lines of light.
Can be classified as transparent, translucent andopaque.
TRANSPARENT MATERIALWhen light shines on a transparent material itpasses through it, so objects on the other sideof it can be seen clearly.
o When light shines on a translucent material some of the light passes through but many light rays are scattered.
Opaque material When light shines on an opaque material none ofthe light passes through it.
ShadowIs a region without light, forms behind the object.Shadows are also cast by the Moon and the Earth.
Reflecting lightThe way light is reflected from a surface depends onwhether the surface is smooth or rough
Reflections Incident ray – a light ray that strikes a surface Reflected ray – a light ray that is reflected from asurface Normal – a line perpendicular to the surface wherethe incident ray strikes. Angle of incidence – the angle between the incidentray and the normal Angle of reflection – the angle between the reflectedray and the normal Plane mirror – a mirror with a flat surface Image – the appearance of an object in asmooth, shiny surface
Objects with smooth surfaceLight rays are reflected from a smooth surface at the sameangle at which they strike it
Two kinds of imagesThey are real image and virtual image.
Real image Can be formed on a screen. Example: produced on a cinema screen by biconvexlenses.
Virtual image Can’t be projected onto a surface but only appearto exist. Example: in a plane mirror or other smooth, shinysurface.
The periscopeIs an instrument for observation from a concealedposition.
Objects with rough surfaces When light rays strike any objects with roughsurfaces the rays are scattered in differentdirections. Objects that have a rough surfaces : woollenpullover and paper.
Passing light through transparent materialsA ray of light is shone on the side of a glass blockand the ray passes straight through.If the glass block is tilted the ray of light follows thepath.
RefractionIs the bending of the light rayThe angle that the refracted ray makes with thenormal is called the angle of refraction.
The prismWhite light passing through a prism is split up intoits constituent colour, forming spectrum.
The rainbow Weaker rainbow is seen above the first because 2reflections occur in each droplet. In the second rainbow the order of colours isreversed.
ColourIs the visual perceptual property corresponding inhumans to the categories called red, green, blueand others.
When a ray of sunlight strikes the surface of anobject, all different colours in it may be reflected orthey may all be absorbed. All colours that are reflected the object appearswhite. All colours that are absorbed the object appearsblack.
Filtering colours Sheets of coloured plastic or glass can filter thecolours in light. Example : a blue filter allows only blue light to passthrough.
Combining coloursRed, green and blue are called the primary coloursof light.
Colours and paint 3 different colours of paint, ink or dye can be usedto make almost all the other colours. These 3 colours are yellow, magenta and cyan. Tiny dots of the 3 colours form the printed picture.