Light and Shadows Lesson Quiz

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?