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.
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CONNECTING KNOWEDGE WITH PASSION
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
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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
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CONNECTING KNOWEDGE WITH PASSION
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.
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i -S MART L EARNING C ENTRE:: Effects of the Sun
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CONNECTING KNOWEDGE WITH PASSION
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.
i-SMART LEARNING CENTRE ::BLK 713 JURONG WEST ST 71
CONNECTING KNOWLEDGE WITH PASSION #B1-37 S640713 TEL: 6794
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i -S MART L EARNING C ENTRE::
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CONNECTING KNOWEDGE WITH PASSION
i-SMART LEARNING CENTRE ::BLK 713 JURONG WEST ST 71
CONNECTING KNOWLEDGE WITH PASSION #B1-37 S640713 TEL: 6794
1250