p4 light notes

i -S MART L EARNING C ENTRE:: P4 Science (Light)

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CONNECTING KNOWEDGE WITH PASSION

Introduction 1. Energy is the ability to do work. 2. The Sun is our main source of energy. It is an important source of heat and light. 3. All living things depend directly or indirectly on energy from the Sun. (a) Plants make use of light energy from the Sun to make food. (b) Plant-eaters feed on plants for energy. The energy from the plants is transferred to plant-eaters. (c) The energy is finally passed on to animal-eaters that feed on the plant-eaters. (d) The following energy chain traces the flow of energy among animals. It is called a food chain and it always begins with a plant.

4. The Sun provides heat energy to keep the Earth warm enough for the survival of living things. 5. The Sun is important as it ensures the continuity of the water cycle. Heat energy from the Sun enables Water from the Earth's surface to evaporate into water vapour. Light Energy 1. Light is a form of energy that enables us to see. 2. Light sources are things that give off their own light. The Sun is our main source of light. Other light sources include lighted candle, burning wood, a lighted bulb, a lighted fluorescent lamp, lightning, a burning oil lamp, a lighted torch, fireflies, etc.

i-SMART LEARNING CENTRE ::BLK 713 JURONG WEST ST 71

CONNECTING KNOWLEDGE WITH PASSION #B1-37 S640713 TEL: 6794 1250

i -S MART L EARNING C ENTRE::

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Why Do We See Things? 1. We see some objects because they give off light. Light from the object travels into our eyes. For example, the light from a burning flame travels into our eyes so we can see it burning.

2. Some objects however do not give off their own light. We are able to see these objects because light that falls on them bounces off into our eyes. We say that these objects reflect light into our eyes. For example, we can see the table below because light from the ceiling light above falls on the table and is reflected into our eyes.

3. The Moon does not give out its own light. We see the Moon because it reflects light from the Sun into our eyes. Light Passing Through Materials 1. Light can pass (transmit) through some materials but not others. Light transmission varies from material to material. 2. Materials that allow most light to pass through are called transparent materials. When light is shone on a transparent material, light passes through it directly without scattering.i-SMART LEARNING CENTRE ::BLK 713 JURONG WEST ST 71 CONNECTING KNOWLEDGE WITH PASSION #B1-37 S640713 TEL: 6794 1250


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Because the transparent material transmits light without scattering, objects behind it can be seen distinctly. Pure water, clear glass and clear plastic are transparent materials. 3. Materials that allow only some light to pass through them are known as translucent materials. Objects placed behind a translucent material appear blurred and fuzzy. We cannot see objects distinctly through translucent materials because light does not transmit through these materials easily. Examples of such materials include frosted glass and tracing paper. 4. Materials that do not allow light to pass through are known as opaque materials. We cannot see objects placed behind them because opaque materials do not transmit light. 5. The classification table below groups materials according to whether they are transparent, translucent or opaque.

Absorption of Light 1. Materials can absorb light and heat energy. The amount of light that can be absorbed depends on the material, its colour and the nature of its surface. 2. A shiny and polished surface absorbs very little light. Most light that falls on it is reflected. A dull surface, however, absorbs more light and reflects less light. 3. A block surface absorbs most of the light that falls on it whereas a white surface absorbs very little light. How are Shadows Formed? 1. Shadows are formed because light which travels in straight lines sometimes get blocked by objects. 2. A shadow is the area of dark space that light cannot reach. 3. Opaque objects cast very dark shadows. Translucent objects cast lighter shadows.i-SMART LEARNING CENTRE ::BLK 713 JURONG WEST ST 71 CONNECTING KNOWLEDGE WITH PASSION #B1-37 S640713 TEL: 6794 1250


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4. An object can cost shadows of different shapes and sizes. 5. Any object that blocks the path of light and prevents light from reaching a surface cast a shadow 6. A shadow always form on the opposite side of the object 7. The shape and size of the shadow of an object changes according to the position of the object and the position of the light source.



i -S MART L EARNING C ENTRE:: Effects of the Sun

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1. The Sun rises in the East and is low in the sky in the morning. The shadows cast by the objects outdoors are thus long and points to the west. 2. As the Sun rises higher into the sky, the shadows get shorter 3. At noon, the shadows are very short as the Sun is directly above. 4. After noon, the shadows get progressively longer, and they point to the east. 5. Hence, the shadows formed in the evening are long and they point to the east.




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p4 light notes

Documents

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light transmission

light passing

use of light energy

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