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Which of the following is an example of a luminous object?
Which of the following is an example of a luminous object?
Illuminated objects can emit their own light.
Illuminated objects can emit their own light.
False
What is bioluminescence?
What is bioluminescence?
The production and emission of light by living organisms.
A ____ year is a unit of distance used in astronomy to describe how far light travels in one year.
A ____ year is a unit of distance used in astronomy to describe how far light travels in one year.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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What natural phenomenon is described by the blocking of sunlight during a solar eclipse?
What natural phenomenon is described by the blocking of sunlight during a solar eclipse?
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A converging beam of light spreads out from a point.
A converging beam of light spreads out from a point.
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What role does the Sun play in maintaining life on Earth?
What role does the Sun play in maintaining life on Earth?
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What type of image is created by a mirror?
What type of image is created by a mirror?
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What is the approximate speed of light in kilometers per second?
What is the approximate speed of light in kilometers per second?
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Light can bend around objects, allowing shadows to form anywhere.
Light can bend around objects, allowing shadows to form anywhere.
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What is the purpose of a pinhole camera?
What is the purpose of a pinhole camera?
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A shadow can be formed by a translucent object blocking light.
A shadow can be formed by a translucent object blocking light.
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What causes shadows to vary in size and shape?
What causes shadows to vary in size and shape?
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When light rays strike a mirror, they __________ back.
When light rays strike a mirror, they __________ back.
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Match the following concepts with their descriptions:
Match the following concepts with their descriptions:
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A ______ is a celestial event where one opaque body blocks the light from another body.
A ______ is a celestial event where one opaque body blocks the light from another body.
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Match the following objects with their ability to allow light to pass through:
Match the following objects with their ability to allow light to pass through:
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How do sundials utilize shadows?
How do sundials utilize shadows?
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Transparent objects can create shadows.
Transparent objects can create shadows.
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What happens to the size of shadows when the light source is low in the sky?
What happens to the size of shadows when the light source is low in the sky?
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What occurs during a solar eclipse?
What occurs during a solar eclipse?
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A total lunar eclipse causes the Moon to appear greenish in color.
A total lunar eclipse causes the Moon to appear greenish in color.
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What type of eclipse can be seen by anyone on the night side of the Earth?
What type of eclipse can be seen by anyone on the night side of the Earth?
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A _______ eclipse occurs when the Earth passes between the Sun and the Moon.
A _______ eclipse occurs when the Earth passes between the Sun and the Moon.
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Match the type of eclipse with its description:
Match the type of eclipse with its description:
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During which phase does a solar eclipse occur?
During which phase does a solar eclipse occur?
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The Moon is a transparent body allowing light to pass through.
The Moon is a transparent body allowing light to pass through.
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What is rectilinear propagation?
What is rectilinear propagation?
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Study Notes
Lesson Objectives
- Explain the difference between luminous and illuminated objects, and describe how light travels.
- Use examples of natural phenomena (like eclipses and pinhole cameras) to demonstrate how shadows and images are formed.
- Compare and contrast shadows and images, explaining how mirrors form clear images and how pinhole cameras capture images differently.
Key Words
- Luminous object: An object that emits its own light.
- Illuminated object: An object that doesn't produce light but reflects light from a luminous source.
- Bioluminescence: The production of light by living organisms.
- Solar energy: Light energy from the Sun.
- Solar eclipse: The Moon blocks the Sun's light from reaching Earth.
- Lunar eclipse: The Earth blocks the Sun's light from reaching the Moon.
- Virtual image: An image that appears to be behind the mirror but isn't actually there.
- Converging beam: Light rays coming together.
- Diverging beam: Light rays spreading out.
- Rectilinear propagation: Light travels in straight lines.
- Transparent: Allows light to pass through completely.
- Translucent: Allows some light to pass through, but objects behind appear blurry.
- Opaque: Does not allow light to pass through.
Light as a Source of Energy
- Solar energy: Light from the Sun provides energy that can be harnessed for power through solar panels.
- Natural source: Sunlight is a natural source of light and energy, driving processes like photosynthesis.
- Keeps Earth warm: The Sun's light helps keep Earth warm, enabling life by maintaining the planet's temperature.
How would life on Earth be affected if solar energy were suddenly unavailable?
- Consider the impact on plants, animals, and human activities.
A Light Year
- A light year is a unit of distance used in astronomy to describe how far light travels in one year.
- Light travels at approximately 299,792 kilometers (or about 186,282 miles) per second.
- A light year equals about 9.46 trillion kilometers (or 5.88 trillion miles).
Objects and Shadows
- Transparent: Allows light to pass through completely, so objects behind can be seen clearly (e.g., clear glass, clean water).
- Translucent: Allows some light to pass through, but objects behind appear blurry or unclear (e.g., frosted glass, wax paper).
- Opaque: Does not allow light to pass through; objects behind cannot be seen at all (e.g., wood, metal, brick).
When is a shadow formed?
- A shadow is formed when an opaque object blocks the path of light.
- Light Source: A shadow occurs in the presence of a light source (natural or artificial).
- Opaque Object: Only opaque objects create shadows because they block light.
- Positioning: The position of the object relative to the light source affects the size and shape of the shadow (shadows are longer when the light source is low in the sky).
- Surface: The texture and color of the surface on which a shadow is cast can influence how the shadow appears.
Subject Enrichment Activity
- Eureka Activity: Textbook page number 165. Post images in GC.
Let's Think
- Artists and photographers pay attention to shadows for artistic effect.
- Using translucent objects instead of opaque ones would create different effects on the image.
- Shadows can be used to tell time (e.g., sundials).
Eclipse
An eclipse is a celestial event where one opaque body (like the Moon or Earth) blocks the light from another body, resulting in a shadow.
- Types of eclipses:
- Solar eclipse: The Moon passes between Earth and the Sun.
- Lunar eclipse: The Earth passes between the Sun and the Moon.
Solar Eclipse
- Total Solar Eclipse: The Moon completely covers the Sun and the Sun's corona (outer atmosphere) is visible.
- Partial Solar Eclipse: Only a portion of the Sun is obscured by the Moon.
- Occurrence: Solar eclipses occur during a new moon phase when the Sun, Earth, and Moon align, however this doesn't always occur.
Lunar Eclipse
- Total Lunar Eclipse: The entire Moon passes through the Earth's umbra (darkest part of its shadow), and the Moon often appears reddish or coppery.
- Partial Lunar Eclipse: Only a portion of the Moon enters the Earth's umbra, resulting in some parts of the Moon being darkened.
- Occurrence: Lunar eclipses occur during a full moon phase when the Sun, Earth, and Moon are aligned.
Light travels in straight lines
- Light travels in straight lines through uniform mediums.
- This behavior is known as rectilinear propagation.
- Shadow formation demonstrates that light travels in straight lines.
Beam of Light
- A beam of light is a stream of light rays traveling in the same direction.
- Parallel beams, diverging beams, and converging beams are different types of beams.
Activity Time
- Textbook page 168 has an activity related to light.
Why Does a Mirror Form a Clear Image?
- Mirrors form clear images because of reflection. Light rays strike a shiny, smooth surface of the mirror and bounce back, which we see as an image.
- A virtual image appears behind the mirror not in front of the mirror.
- The smoothness of the mirror's surface is essential for clear reflections.
Images Formed by Plane Mirrors
- Real image: Image from a pinhole camera or other optical devices; the image is in the path of light rays.
- Virtual image: Image from a mirror or a lens; when you look at an object in a mirror, it appears to come from behind the mirror but the light rays do not actually pass through this path.
Let's discuss...
- What are the differences between an image and a shadow?
Pinhole Camera
- A pinhole camera is a simple tool demonstrating how light travels in straight lines.
- It consists of a box with a tiny hole and a translucent screen.
- Light passing through the hole creates an inverted image of objects outside the box on the screen, illustrating the basic principles of light and shadow.
Additional Questions
- In what situations might you see a shadow instead of an image?
- Why aren't solar and lunar eclipses visible from every part of Earth at the same time?
- What happens when the Earth's shadow falls on the Moon? When does such an event occur?
- Why does a plane mirror form a clear image, but a rough floor does not?
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Description
Test your knowledge on the concepts of luminous and illuminated objects, how light travels, and the formation of shadows and images. Explore examples like eclipses and pinhole cameras while comparing the roles of mirrors and other phenomena in image formation.
