Chapter 11 - Light Shadows and Reflection What is light? Light is produced by luminous objects, such as fires, electric lamps and stars like the Sun. The light that we can see is called visible light, light , but there is also light that we cannot see, including ultraviolet light and infrared light.
Features of light: a) b) c) d)
Light Light Light Light Light Light Light
is a form form of of radia radiatio tion n travels travels in in straig straight ht lines lines can trave travell through through empty empty space spaces s is the fastest fastest thing thing there is. In In space its speed speed is 300 000 000 km/s
Source of Light Natural Natural light sources include the following. Sun, lightening, glowing rocks (lava from volcanoes) and flames. Some plants and animals give off light (glow worms and some deep sea fish). Human-made Ther There e are are a lot lot of sour source ces s of huma human n made made ligh light, t, here here are are some some of them them:: candles, light bulbs (in torches, around the house), televisions, fireworks.
Luminous Object: Objects that give out or emit light of their own are called luminous objects. Example: Candle, Sun and other stars Non-Luminous object: Objects that do not have their own light but shines due to reflected light are called non luminous objects. Example: Moon
A ray diagram showing how we can see a luminous object and a non-luminous object
How we can show that light travels in straight line? Take a piece of a pipe or a long rubber tube. Now see through it other end of the tube, keeping tube straight then bend the tube and try to see other end again through this tube. You will observe if tube is straight we can see other end clearly but if tube is not straight then we can not see other end of the tube. This shows light travels in a straight line.
What will happen when light hits an object? Four Four diff differ eren entt thin things gs can can happ happen en when when ligh lightt hits hits an object: The wave waves s can can be reflected or scattered off off the the 1. The object. 2. The waves can be absorbed by the object. 3. The waves can be refracted through the object. (light ray bend) 4. The waves can pass through the object with no effect
Transparent, Translucent and Opaque Materials 1. Transparent: Transparent objects let light pass through without scattering the rays. Example: plastic bottles, windows and clear glass 2. Translucent: A translucent object lets some light through but it scatters the rest of the light so much that whatever is on the other side cannot be seen clearly. Example: Frosted glass, butter paper, oiled paper, fog, tissue paper 3. Opaque: Materials that do not allow light to pass through are called opaque materials. Some of the light is absorbed by the material and some is reflected. Example: metals, wood, rock, book
Shadow: The shadow is the darker region where the light is blocked. Light travels in straight lines, so it can not reach this region. Shadow Depends on Source of light Point source of light (bulb): We will get sharp and dark shadow on the screen.
If source of light is wide then shadow will have two parts: Umbra-An "umbra" is the part of the shadow where all of the light from the source is blocked by the shadowing object. Penumbra-A "penumbra" is that region around the umbra where the shadow is only partial, or imperfect.
Factors on which shape of the shadow depends • • •
the shape of the object the position of the source of light and the size of the source of light.
Why the shadow formed by a flying airplane/bird is not formed on the earth? We cannot see shadow because the umbra is formed close to the object and the penumbra is too large and too faint to be visible.
Reflection of light: Sending back of light by objects is called reflection of light. a) Regular reflection: When a beam of light falls on a smooth surface, all the rays of the beam are reflected in only one direction. This is called regular reflection. b) Irregular reflection: When a beam of light falls on an object with an uneven surface they get reflected in different directions. This is called irregular reflection or diffused reflection.
Pin Hole Camera A pinhole camera is a camera in which the lens is replaced by an extremely small hole, pierced in very thin material. Light from a scene passes through this single point, producing a more-or-less sharp image on the rear of a light-proof box. The image is upside-down, as in a conventional camera with a lens
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