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Science Class 10 - Light Reflection-And-Refraction Notes

Comprehensive study notes for Class 10 - Light Reflection-And-Refraction olympiad preparation

Light: Reflection and Refraction

Welcome to the chapter on Light: Reflection and Refraction for Class 10. In this chapter, you will learn about the nature of light, how it behaves when it meets different surfaces, and the laws that govern its reflection and refraction. By the end of this chapter, you will be able to explain and solve problems related to mirrors, lenses, and the bending of light.

Key Concepts

  • Light: A form of energy that enables us to see objects.
  • Reflection: The bouncing back of light from a surface.
  • Refraction: The bending of light as it passes from one medium to another.
  • Mirror: A smooth, shiny surface that reflects light.
  • Lenses: Transparent objects that refract light to form images.

Reflection of Light

When light falls on a smooth surface like a mirror, it bounces back. This is called reflection.

  • Incident Ray: The ray of light that falls on the surface.
  • Reflected Ray: The ray of light that bounces off the surface.
  • Normal: An imaginary line perpendicular to the surface at the point of incidence.
  • Angle of Incidence (i): The angle between the incident ray and the normal.
  • Angle of Reflection (r): The angle between the reflected ray and the normal.

Laws of Reflection:

  • The angle of incidence is equal to the angle of reflection.
  • The incident ray, the normal, and the reflected ray all lie in the same plane.

Refraction of Light

When light passes from one medium to another (like air to water), it bends. This bending is called refraction.

  • Incident Ray: The ray entering the new medium.
  • Refracted Ray: The ray that bends in the new medium.
  • Angle of Incidence: The angle between the incident ray and the normal.
  • Angle of Refraction: The angle between the refracted ray and the normal.
  • Optical Density: How much a medium slows down light.

Laws of Refraction (Snell's Law):

  • The incident ray, the refracted ray, and the normal all lie in the same plane.
  • The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media (n₁sin i = n₂sin r).

Images Formed by Mirrors and Lenses

  • Plane Mirror: Forms virtual, erect images of the same size as the object.
  • Concave Mirror: Can form real or virtual images depending on the object's position.
  • Convex Mirror: Always forms virtual, diminished images.
  • Convex Lens: Can form real or virtual images; used in magnifying glasses.
  • Concave Lens: Always forms virtual, diminished images.

Applications

  • Mirrors are used in vehicles, dressing tables, and periscopes.
  • Lenses are used in spectacles, cameras, and microscopes.
  • Refraction explains why a pencil looks bent in water and how rainbows form.

Practice Questions

  1. State the laws of reflection of light.
  2. What is refraction? Give one example from daily life.
  3. Draw a ray diagram to show the reflection of light from a plane mirror.
  4. What type of image is formed by a convex mirror?
  5. Explain why a coin appears raised when placed in a bowl of water.

Challenge Yourself

  • Find the refractive index of glass if the angle of incidence is 30° and the angle of refraction is 19° (use Snell's Law).
  • Design an experiment to show the bending of light using a glass slab.

Did You Know?

  • The speed of light in air is about 300,000 km/s, but it slows down in glass or water.
  • Mirages in deserts are caused by the refraction of light.

Glossary

  • Reflection: Bouncing back of light from a surface.
  • Refraction: Bending of light as it passes from one medium to another.
  • Normal: An imaginary line perpendicular to a surface.
  • Refractive Index: A measure of how much a medium slows down light.

Answers to Practice Questions

  1. 1. The angle of incidence is equal to the angle of reflection. 2. The incident ray, normal, and reflected ray all lie in the same plane.
  2. Refraction is the bending of light as it passes from one medium to another. Example: A pencil appears bent in a glass of water.
  3. [Students should draw a ray diagram showing incident ray, reflected ray, and normal on a plane mirror.]
  4. A convex mirror forms a virtual, diminished, and erect image.
  5. Due to refraction, light bends as it moves from water to air, making the coin appear raised.

Explore the wonders of light by observing reflections and refractions around you!

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