Importance of Light:
- Light energy is required for food, oxygen and fuel
- Green plants prepare their food during photosynthesis in the presence of sunlight.
- Plants utilise carbon dioxide and release oxygen, a life supporting gas.
- The energy of the fossil fuels has been derived from the light energy of the sun.
- The fossil fuels are formed by the dead and decayed organisms, that release their nutrients back into nature.
What is the colour of the Sunlight?
- The colour of the sunlight is white.
- When the sunlight is passed through a prism, it splits into seven colours as VIBGYOR – Violet, Indigo, Blue, Green, Yellow, Orange, Red
How do we see various colours around us?
- The objects absorb specific colours of light and reflect the other colours.
- The reflected colour is the colour of the object
- For example, Leaves cannot absorb green colour and hence it is reflected back, this is visible to our eyes.
What are the various sources of light?
- The objects that emit light are called as sources of light.
- There are two sources of light. Natural and Manmade.
- Sun, Stars, Fireflies are the natural sources of light.
- Electric bulb, tube light, burning lamp are the man made source of light
Difference between Luminous and Nonluminous source of light?
| Luminous object | Non luminous object |
| The object that produces light on their own is called as luminous object | The object that does not emit light on their own is called as Non luminous object |
| Ex: Sun, Star, Fireflies | EX: Moon, Earth |
What are the hot source and cold source of light?
- The objects that become hot when they emit light are called as hot source of light. Ex: Sun, Candle, Electric bulb.
- The objects that emit light without becoming hot is called as cold source of light. Ex: Fireflies
Define Bioluminescence?
- A natural phenomenon of emitting light by an object is called as Bioluminescence.
- They convert chemical energy into light energy.
- Ex: Phytoplankton, Fireflies, Jellyfish, algae etc.
What is Rectilinear Propagation of Light?
The property of light travelling in a straight line is called as rectilinear propagation of light
Define Ray?
- Narrow path of the light represented by a line with an arrowhead showing the direction in which it is travelling is called as ray of light.
- Beam of light is broader an consist of several rays.
- When beam of light moving away from each other is called as Divergent rays.
- When beam of light moving towards each other and meet at a common point is called as Convergent rays.
Define Transparent object with example?
- Objects that allow the light to completely pass through them are called as Transparent objects.
- Ex: Water, glass etc.
Define Translucent object with example?
- Objects that allow light to partially pass through them are called as Translucent objects.
- Ex: Butter paper, thin sheet of plastic
Define Opaque objects with example?
Objects that do not allow light to pass through them are called as Opaque objects. Ex: Wood etc.
What is a Shadow?
When an opaque object is placed in the path of light, dark portion is formed on the opposite side of the object on the screen/ wall. The dark portion is called as Shadow.
What are the various characteristics of shadow?
- Shadows can only be seen on screen, wall, building, ground etc.
- Shadows are black in colour and it is not changed by the colour of the opaque objects.
- The size of shadow depends on distance of source of light and an angle at which light rays fall on the object.
- If the source of light is closer to object, larger shadow is formed and smaller shadows are formed when the source of light is far away from the object.
What are the categories of Shadow?
The Shadow is categorized into two parts based on the brightness of the dark patches.
Umbra:
Umbra is the darkest part of the shadow present in the middle of it. It is formed when there is complete absence of light
Penumbra: It is the faintest part of the shadow present on the corners. It is formed when the light is not completely blocked.
What is an Eclipse?
- The Eclipse are formed on the basis of the rectilinear propagation.
- They are shadows formed naturally when the Sun, Moon and Earth aligned in a straight line
Define Solar Eclipse?
- During Solar Eclipse, when the Moon is between the Sun and Earth, Moon cast its shadow on the Earth
- Solar Eclipse will always take place in a New Moon Day
- Depending the shadow type, Solar Eclipse can be a Total Solar Eclipse (Sunlight is completely blocked by the Moon and its Shadow falls on the Earth) or Partial Solar Eclipse
- (Sunlight is partially blocked by Moon, a part of the shadow falls on the Earth)
Define Lunar Eclipse?
- When the Sun, Moon, Earth come in a straight line, with the Earth in the middle, the Shadow of the Earth falls on the Moon.
- Lunar Eclipse occurs only on a Full Moon Day.
- Depending on the Shadow type, total Lunar Eclipse and Partial Lunar Eclipse takes place.
What is a Pin hole camera?
- Pin hole camera is a small camera made up of cardboard.
- It does not have any lens
- It has a small opening as pin hole, through which the light passes and we see the image as inverted.
- The Pinhole camera works on the principle of Rectilinear Propagation of Light.
What type of Image is formed in a Pin hole Camera?
- The Image in the Pin hole camera is
- Inverted
- Image is real, that is image is formed on the screen
- Image has the same colour of the object
- The Image formed may be smaller, bigger or same as that of the object.
How does a Pin hole camera work?
- Light from the outside passes through the single hole.
- An inverted image is formed on the opposite side of the object.
- This is because the light rays coming from the top and bottom of the object intersect at the pinhole
- The smaller the hole, sharper the image
- Human Eye in a bright light is similar to a Pinhole Camera.
What are the advantages of the Pinhole?
- The Pinhole camera is used to view the image of the objects around us.
- It is also used to take the photograph of the object, if a photographic film is placed on the screen
What is Reflection?
When a light falls on the polished surface of an object, it bounces back that is it gets reflected, this is called as Reflection of Light.
What is a Mirror?
- Mirror is a surface, typically of glass coated with metal amalgam, that reflects the clear image
- Mirrors reverse the direction of image in an equal yet opposite angle from which light shines on it
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