빛┃빛과 파동 (1/2)｜중2과학

Main ideas / lessons (Unit 3: Light and Waves – Part 1: Light)

Curriculum overview

Unit 3 (Intermediate Science) is split into:

• Part 1: Light
• Part 2: Waves

The light portion focuses on:

• The path and characteristics of light
• Mirrors and lenses as tools that use the behavior of light

Why we can see

• The human eye detects light and sends signals to the brain, which helps identify shapes.
• Without light, you can’t see objects clearly, and it’s difficult to discern shapes with the naked eye.
• Objects can be seen in two ways through light:
  • Self-luminous objects: you see them by receiving the light they emit.
  • Non-self-luminous objects: you see them by receiving reflected light from their surface.
• An object that emits light on its own is called a light source.

How light moves and changes

• Light travels in a straight line.
• When light hits/passes through something else, its path changes due to:
  • Reflection: light bounces off an object.
  • Refraction: light bends as it passes through a different medium.

Rules for reflection and refraction

• Reflected/refracted rays do not change randomly; they follow specific rules.

Law of reflection (mirrors)

• Draw an imaginary line perpendicular to the mirror surface (the normal).
• The angle of incidence = angle of reflection, measured relative to the normal.

Refraction (bending at a boundary)

• When light enters a different material (example: air → water), it bends at the boundary because the substances differ.
• An angle of incidence and an angle of refraction form relative to the normal.
• The amount of refraction depends on the material the light passes through.

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Mirror types and what changes in images

Flat mirror

• Ordinary mirrors people use for appearance are flat mirrors.
• Because reflection sends light out at the same angle it entered:
  • The image size equals the object size
  • The image has the same shape as the object
  • The image is symmetrical with respect to the mirror

Convex mirror (bulging outward)

• The reflecting surface is curved, but the law of reflection still applies.
• Example light paths described:
  • One ray goes toward the center direction.
  • Another ray hits the surface at some angle.
• After applying the reflection rule (incidence angle = reflection angle relative to the normal), the reflected rays appear to meet again at a point, creating a reflected image.
• As the distance from the mirror changes:
  • The position and angle of reflected light change
  • This changes how the reflected image forms
• Overall implication: convex mirrors form images based on where the reflected rays appear to meet after reflecting from a curved surface.

Concave mirror (curving inward)

• The same reflective principle applies, based on the mirror’s curvature.
• Example light paths described:
  • One ray moves toward the center of the mirror.
  • Another ray hits the mirror surface.
• By ensuring incidence and reflection angles follow the rule relative to the normal:
  • The rays reflect outward and can form an enlarged image under certain conditions.
• As the distance to the mirror increases:
  • The image position/size changes
  • At some point it becomes an inverted, small image (example phrased as “small shark”)

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Lens types and refraction-based image formation

Mirrors vs lenses

• Mirrors: reflect light.
• Lenses: refract light and let it pass through.
• The amount of refraction depends on:
  • Convex lens vs concave lens
• This principle underlies glasses.

Convex lens

• Two example rays from an object/light source:
  • One ray passes through the center of the lens (travels straight).
  • The other ray hits the lens surface and is refracted downward along the normal.
• The refracted rays meet behind the viewer, forming a magnified enlarged image.
• As the object distance increases:
  • The angles/positions of refraction change
  • This leads to different image outcomes

Concave lens

• Two rays are described:
  • One travels straight through the center (not bent at the center).
  • Another ray hits the lens surface and is refracted upward.
• The two rays then meet and form a smaller image.
• As distance increases, the image changes accordingly.

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Color of objects and light mixing (RGB and additive color)

How we perceive color

• The color of an object depends on the light it reflects (what reaches our eyes).
  • Example: a watermelon appears green because it reflects green light.
• If an object absorbs all light, it appears black.

White light concept

• Combining lights of red, orange, yellow, green, blue, and violet produces white light.

Screens and pixel representation

• Monitors and smartphones display color using light synthesis.
• Resolution labels such as 720p, 1080p, etc., are mentioned.
  • P stands for pixel
  • A pixel is a small colored dot on a screen
• By printing many small colored dots, screens create many colors.

Primary colors of light (additive mixing)

• The three primary colors are RGB:
  • Red, Green, Blue
• RGB lights can produce many colors via additive mixing:
  • Red + Blue = Magenta
  • Red + Green = Yellow
  • Blue + Green = Cyan
  • Red + Green + Blue = White
• Further combinations produce countless colors.

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Speakers / sources featured

• No specific named speakers are mentioned in the provided subtitles; the narration appears to come from a video presenter/instructional voice.