Light
Types of Objects
Light Rays
Light is electromagnetic radiation that can be detected by the human eye. Its a form of energy.
Luminous Objects
Non-Luminous Objects
The luminous objects are visible as they emit light on their own.The sun and candle are the two examples.
The non-luminous objects are visible because of luminous objects. They are formed when Luminous objects reflect light on them. The moon and plants are the two examples.
Opaque
Translucent
Transparent
If light hits an object and passes through it, that object is known as a transparent object.
Translucent materials allow light to pass through them, but they diffuse the light in a way that make objects on the opposite side appear blurred. Examples of translucent materials are frosted glass, oil paper, some plastics, ice and tissue paper.
There are certain objects through which light cannot pass, and it changes its path after hitting the object. These are called Opaque objects. Some examples are wood, mobile phone and us humans.
Light leaves the surface of a luminous object in all directions but if some of the light is made to pass through a hole it can be seen to travel in straight lines. These are called Light Rays. For example, when sunlight shines through a small gap in the clouds, it forms broad sunbeams with straight edges.
Shadows
Transparent, Translucent and Opaque Shadows
The object must be opaque or translucent to make a shadow.
A transparent object will not make any shadow, as light will pass straight through it.
Opaque objects make dark shadows. Translucent objects make faint shadows.
Formation of Shadows
Size and Intensity of Shadows
A shadow is made when an object blocks light. The shadow appears on the side of the object furthest from the light source.
Size of the light source
Distance between the light source ad the object
A light shadow is formed when the light source is close to the object and a dark shadow is formed when the light source is farther from he object.
A small light source gives a sharp shadow that is equally dark all over.
A larger light source gives a shadow with a dark central region and a lighter shadow surrounding it.
Reflection
When light falls on a shiny surface, it bounces back. This phenomenon is called reflection. We are able to see images in mirrors or in water, because of reflection.
Waves
Electromagnetic Waves
Mechanical Waves
Mechanical Waves require a medium to travel. One such example is Sound.
Electromagnetic waves require no medium to travel. They have EMR or Electromagnetic Spectrum. Some examples include X-Rays, Gamma Rays, Visible Light, UV Rays, etc.
Refraction
Reflection from a Rough Surface
Reflection of Light from a Smooth Surface
Most of the objects on Earth have rough surfaces. These type of objects scatter the light that falls on them in different directions. Example - Sweater, Roads, Doors, Tables, Chairs, Electronic Devices, etc.
The reflection that takes place on such surfaces is irregular and no images are formed.
Regular Reflection of Light from a Plane Surface
Reflection of Light from a Plane Mirror
Angle of Incidence
It is the angle formed by the incident ray and the normal.
Angle of Reflection
Angle formed by the reflected ray and the normal.
Plane Mirror
A plane mirror is a mirror with a flat surface.
Image
An image is the appearance of an object in a smooth and shiny surface. It is produced by the light from the object being reflected by the surface.
Periscopes
Some examples of objects with smooth surfaces are Glass, Water, Polished Metal, etc.
Periscopes are an application of reflection by plane mirrors.
Periscopes are 2 plane mirrors placed in a peculiar way to make things visible.
When this type of reflection takes place light rays don’t get scattered and an image is produced.
Types of Images
Real Images
Virtual Images
These can be produced on screens. Eg- Movie projected on the cinema screen.
Virtual Images can’t be projected onto a surface but only appear to exist.
Example: Our image in a plane mirror, our image in a glass, etc.
In a plane mirror, our image is
The image is behind the mirror.
It is erict and not upside down.
The distance between us and the mirror and our image in the mirror appears to be the same.
The size is the same as well.
It is the wrong way around. For example - Our left hand appears to be the right hand of our image in the mirror.
Umbra Region
Penumbra Region
It is the part of the shadow which is completely dark. It receives no light.
The partially dark part of the shadow. This region receives some light from the light source.
Light gets refracted when the incident ray is 90 degrees to the surface of the material.
Refraction is the bending of light. It happens due to change in speed of light.
Light travels at different speeds in different media.
Normal
Normal is a line that’s perpendicular (at 90 degrees) to the surface where the incident ray strikes.
Refracted Ray
Light Ray that gets refracted after it strikes the surface.
Angle of Incidence
It is the angle between the incident ray and the normal.
Angle of Refraction
It is the formed by the refracted ray and the normal.
Incident Ray
Light Ray that fall on the surface.
From a rarer medium to a denser medium.
From a denser medium to a rarer medium.
In this light bends towards the normal.
Light bends away from the normal.
Prism
Prism is a glass or a plastic block with a triangular cross section.
When a ray of sunlight passes through a prism, it splits into seven colours. This is known as Spectrum.
Rainbow
VIBGYOR
It is produced by the refraction and reflection of the Sunlight through the rain drops.
Each colour produced has a different wavelength.
When they travel through a prism, the speed of each of their wavelengths is different.
They spread out to form the colours of the spectrum. This process is called Dispersion.
The light waves with the longest wavelengths are slowed down the least and are refracted the least (Red).
The light waves with the shortest wavelengths are slowed down the most and are refracted the most (Violet).
Path of Light
The path of light can be seen if something is present is the air obstructs. This is called Tyndall Effect.
Light travels in the form of smaller lines of light called Rays.
Light always travels in Straight Lines.
Sunlight/Whitelight
They contain light waves of 7 different coloured wavelengths. These can be seen through dispersion fo Light.
When a ray of sunlight strikes an object we see colours.
Combining Colours
Filtering Colours
Absorbing and Reflecting Colours
The Object may reflect all the different colours. If this happens then it’s colour appears to be white.
The Object may absorb all the different colours. In this case the colour appears Black.
The object may absorb some colours and reflect the others.
The colour of the object is a combination of the colours reflected.
Eg. A yellow sunflower appears to be yellow as it absorbs all other colours and reflect yellow.
Sheets of Coloured plastic and glass can filter the colours.
They absorb some colours and allow the other colours to pass-through.
They produce different coloured light.
Eg. A blue filter allows only blue light to pass through.
Eg. A red allows only red light to pass through.
Used in
Theatre for added effects
Scientific Investigations
Photography for Art exhibitions, Advertising campaign
Coloured Paint
Primary Colours
Yellow, Magenta, and Cyan
Mixing all of them together produces black
They can be combined in different proportions to produce a wide range of colours
The pigment absorbs some of the colours of light and reflects others,
This gives the pigment its distinct colour.
Paint contains tiny particles known as pigment
Coloured Light
Lights of different colours combine to form other colours.
Primary Colours
They combine to form Secondary colours
Red, Blue and Green
These are set of 3 colours which can combine to form all other colours.
Mixing all of them produces white