Light, Shadows and Reflections
1. What is light?
Ans Light is a source of energy that enables us to see things around us.
Sources of Light
Natural sources Man made sources
Sun, Stars, fireflies, etc. bulb, torch, etc
Luminous bodies- bodies that emit their own light are called luminous bodies. eg Sun
Non Luminous bodies- bodies that don't emit their own light but reflects light that falls on it is called non luminous bodies. eg Moon, chair, table.
Moon is a natural non-luminous body which doesn't have light of its own but reflects the light of the Sun.
Light travels in a straight line. When we want to represent the propagation of light, we draw a ray.
When a group of rays moving in an organised manner it is called a beam of light.
2. What is Rectilinear propagation of light?
Ans The property of light to travel in a straight line is called Rectilinear propagation of light.
Ans Aim - To prove that light travels in a straight line
Materials required- 2 ft long rubber tube, candle, matchbox, plastic tube.
Procedure- Take a hollow plastic tube which can be bend easily. Light a candle and put it on a stand at a distance of 3 ft away from you. Observe the candle flame through the hollow tube. Now bend the tube and again try to see through it.
Observation- We will not be able to see when the tube is bend as light can't travel a curved path it can travel in a straight line.
Conclusion- The activity is proving that light travels in a straight line.
1. Transparent materials
2.Translucent materials
3. Opaque materials
Materials that allow light to pass through it is called transparent materials. We can see through it clearly. eg glass, plastic cover, etc
Translucent materials
Materials that allow little light to pass through it is called translucent materials. We can see through it but the image won't be clear. eg butter paper, muddy water, etc
Opaque materials
Materials that don't allow light to pass through it is called opaque materials. We cannot see through it. eg cardboard, brick, etc.
Refection
of light
When a ray of light falls on a smooth polished surface, it bounces back. This is known as reflection of light. the bouncing back of light results in the formation of an image.
Plain Mirror
It is a thin, flat, smooth sheet of glass having a shiny coating of silver coating and paint.
4.give any four phenomena that suggest that light travels in a straight line.
Ans 1.Formation of shadow.
2. A beam of light from the projector.
3. The headlight of a car when it is switched on.
4. When ray of light enter a dark room.
5. What is a pin hole camera?
Ans A pin hole camera works on the principle of rectilinear propagation of light. It demonstrates how light forms images of objects.
6. What are the properties of an image formed in a pin hole camera?
Ans 1.The image formed in a pin hole camera is inverted.
2. Diminished and details of the image such as colour, etc are clear in the image.
7. Why are the surfaces of a pin hole camera black?
Ans A black surface absorbs light rays thus, any extra light enters from the sides is absorb by it. This helps as to see the image clearly. If we don't paint the sides black, the image may appear or maybe dull.
8. What is a shadow? Mention the conditions required to form a shadow.
Ans A dark patch formed behind an opaque body when it is places in the path of light is called a shadow.
There must be a -
1. Source of light
2. An opaque object
3. An opaque screen to form a shadow.
9. How is an image formed in a pin hole camera?
Ans Luminous objects emit light in all directions. for example take two points P and Q that is the top of the candle and the base of the candle. A ray of light starting from point P will pass through the pin hole and meet the screen at P1, another ray of light starting from point Q will pass through the pin hole camera and meet the screen at Q1. The ray starting from different points between P and Q will meet he screen in between P1 and Q1 and thus form an inverted image of the object. Pin hole camera works on the principle of rectilinear propagation of light.
Plain Mirror
It is a thin, flat, smooth sheet of glass having a shiny coating of silver coating and paint.
4.give any four phenomena that suggest that light travels in a straight line.
Ans 1.Formation of shadow.
2. A beam of light from the projector.
3. The headlight of a car when it is switched on.
4. When ray of light enter a dark room.
5. What is a pin hole camera?
Ans A pin hole camera works on the principle of rectilinear propagation of light. It demonstrates how light forms images of objects.
6. What are the properties of an image formed in a pin hole camera?
Ans 1.The image formed in a pin hole camera is inverted.
2. Diminished and details of the image such as colour, etc are clear in the image.
7. Why are the surfaces of a pin hole camera black?
Ans A black surface absorbs light rays thus, any extra light enters from the sides is absorb by it. This helps as to see the image clearly. If we don't paint the sides black, the image may appear or maybe dull.
8. What is a shadow? Mention the conditions required to form a shadow.
Ans A dark patch formed behind an opaque body when it is places in the path of light is called a shadow.
There must be a -
1. Source of light
2. An opaque object
3. An opaque screen to form a shadow.
9. How is an image formed in a pin hole camera?
Ans Luminous objects emit light in all directions. for example take two points P and Q that is the top of the candle and the base of the candle. A ray of light starting from point P will pass through the pin hole and meet the screen at P1, another ray of light starting from point Q will pass through the pin hole camera and meet the screen at Q1. The ray starting from different points between P and Q will meet he screen in between P1 and Q1 and thus form an inverted image of the object. Pin hole camera works on the principle of rectilinear propagation of light.
10 What will happen if the pin hole of the pin hole camera becomes bigger?
Ans If the pin hole of the pin hole camera becomes bigger one ray of light from the given point will enter the pin hole camera. This will result in a an overlapping of the image and a blurred image will be formed.
11. Define a mirror?
Ans A mirror is a smooth polished surface when light falls on it the light bounces back.
12. Differentiate between a shadow and an image formed in a pin hole camera?
Ans Shadow
Shadow is a dark outline formed behind an opaque body. No colours are seen in a shadow except black. They are not inverted . Shadows of an object can be misleading sometimes. Shadows can be smaller or bigger than the object.
Image in a pin hole camera
Image in the pin hole camera shows all the details of the object. All colours are seen in the image of the pin hole camera. Image formed in a pin hole camera is inverted. Image is not misleading. Image is always smaller than the object.
Lateral inversion
The left side of the object appears the right side of the image. This left-right reversal of an object and its mirror image is called lateral inversion.
Real image and Virtual image
Real image- An image that can be obtained on a screen is called real image. It is always inverted. Eg image formed in a pin hole camera
Virtual image- An image that cannot be obtained from the screen is called virtual image. It is always erect. Eg image formed in a plane mirror
13. What happens to the size of a shadow when an object moves towards the source of light and away form the screen.
Ans The size of the shadow increases.
14. what happens to the size of a shadow when an object moves away form the source of light and towards the screen.
Ans The size of the shadow decreases
Thanks, I loved reading this
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