Reflection and Refraction of Light

reflection and refraction of light

Table of Contents

Introduction of Reflection and Refraction

Light:

  • Light is a form of electromagnetic wave that is visible to the human eye.
  • It travels in a straight line and has both wave-like and particle-like properties.

Properties of Light:

  • Wavelength: The distance between two successive peaks or troughs of a light wave.
  • Frequency: The number of wave cycles passing a point per second, measured in Hertz (Hz).
  • Speed: Light travels at a constant speed of approximately 299,792,458 meters per second in a vacuum.

Reflection:

  • When light bounces off a surface, it’s called reflection.
  • Law of Reflection: The angle of incidence is equal to the angle of reflection.

Refraction:

  • Refraction occurs when light changes direction as it passes from one medium to another.
  • It happens due to the difference in speed of light in different mediums.

Nature of Light

Wave Theory of Light

Wave Theory of Light - History, Huygen's Propostions and More

  • Light is considered as a form of energy that travels in the form of waves.
  • These waves can be described by properties like wavelength, frequency, and amplitude.
  • According to this theory, light exhibits properties similar to other waves, like sound waves.

Electromagnetic Spectrum

The electromagnetic spectrum | Microwaves, Infrared, X-rays etc.

  • The electromagnetic spectrum is the range of all types of electromagnetic radiation.
  • It includes various types of waves, such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
  • Visible light is just a small portion of this spectrum, which is why we can only see a limited range of colors.

Ray Diagrams

Importance of Ray Diagrams

  • Ray diagrams are graphical representations used to visualize how light behaves when it encounters surfaces like mirrors and lenses.
  • They help in predicting the path of light rays and determining where they will converge or diverge.
  • Useful for understanding phenomena like reflection and refraction.

What is meant by 'reflection of light'? Define the following terms used in  the study of reflection of light by drawing a labelled ray diagram : a  Incident ray b Reflected ray

Terminology

  • Incident Ray: The ray of light that strikes a surface.
  • Reflected Ray: The ray of light that bounces off a surface after striking it.
  • Refracted Ray: The ray of light that changes direction as it passes from one medium to another.
  • Normal: A line perpendicular to the surface at the point where the incident ray strikes it.
  • Angle of Incidence: The angle between the incident ray and the normal.
  • Angle of Reflection: The angle between the reflected ray and the normal.
  • Angle of Refraction: The angle between the refracted ray and the normal.

Reflection of Light


Laws of Reflection

Statement: The angle of incidence equals the angle of reflection.

Why are rays of light specific/fixed in ray diagrams of spherical mirrors  when we have to find out the position of the image formed by a concave or  convex mirror? If we

Explanation: When light rays strike a smooth surface, the angle at which they approach the surface (angle of incidence) is equal to the angle at which they leave it (angle of reflection).

  • Purpose: Ray diagrams are graphical representations used to visualize the paths that light rays take during reflection.
  • Representation:
    • A straight line (incident ray) approaching a surface at a particular angle.
    • A perpendicular line (normal) drawn at the point of incidence.
    • Reflected ray leaving the surface at the same angle as the incident ray, but on the opposite side of the normal.

Types of Reflection

Specular Reflection (Mirror-like surfaces):

Characteristics:

  • Reflection from smooth and shiny surfaces.
  • Produces a clear and well-defined image.

Molecular Expressions Microscopy Primer: Light and Color - Specular and  Diffuse Reflection: Interactive Tutorial

Examples and Applications:

  • Mirror reflection: Used in mirrors, telescopes, and magnifying glasses.
  • Metallic surfaces: Used in car paint and reflective coatings.

Diffuse Reflection (Rough surfaces):

Characteristics:

  • Reflection from rough and irregular surfaces.
  • Scatters light in many directions.

Examples and Applications:

  • Wall paint: Helps in illuminating rooms evenly.
  • Clothing materials: Ensures non-glaring appearance.

Spherical Mirrors

Concave Mirror:

  • Shape: Curved inward like a cave.
  • Characteristics:
    • Can produce both real and virtual images.
    • Focuses light rays to a focal point.

Concave Mirrors and Convex Mirrors - Ray Diagrams, Image Formation, Examples

Convex Mirror:

  • Shape: Curved outward like a bulge.
  • Characteristics:
    • Always produces virtual and erect images.
    • Diverges light rays, no real focal point.

Focal Points and Image Formation

Image Formation by Lenses and the Eye

Concave Mirror:

  • Ray 1: Parallel ray passing through the focal point after reflection.
  • Ray 2: Ray passing through the focal point before reflection and reflecting parallel.
  • Image Formation: Depending on the object’s position:
    • Real and inverted when beyond the focal point.
    • Virtual and upright when between the focal point and the mirror.

Convex Mirror:

  • Ray 1: Parallel ray diverging after reflection.
  • Ray 2: Ray directed towards the focal point but does not reach it.
  • Image Formation: Always forms a virtual and erect image.

Refraction of Light

Refraction

What is refraction of light? Draw the diagram of refraction of light in a  glass slab. Write laws of refraction.

  • Light bends when it moves from one medium to another due to the change in speed of light.
  • Light travels slower in denser media like glass or water compared to air.

Refractive Index

  • Refractive index (n) is a measure of how much light slows down when entering a medium.
  • It is defined as the ratio of the speed of light in vacuum to the speed of light in the medium.
  • Formula: where is speed of light in vacuum and is speed of light in the medium.

Snell’s Law

Snell's Law -- The Law of Refraction

  • States the relationship between angles of incidence and refraction and their respective refractive indices.
  • Mathematical Expression:
  • and are refractive indices of the two media, is the angle of incidence, and is the angle of refraction.

Using Snell’s Law:

  • Example: If light travels from air (n=1) into water (n=1.33) with an angle of incidence of 30°, find the angle of refraction.
  • Solution:
  • Solving gives .

Applications of Refraction

  • Mirage Formation: Due to bending of light as it passes through layers of hot and cold air close to the ground.
  • Working of Lenses: Uses refraction to focus light and form images (like in cameras and eyeglasses).
  • Prisms and Dispersion of Light: Light is split into its component colors (spectrum) as it passes through a prism due to varying refractive indices for different wavelengths.

Comparison Table: Reflection vs. Refraction

Criteria

ReflectionRefraction
DefinitionThe bouncing back of light when it hits a surface.The bending of light as it passes from one medium to another.
CauseInteraction of light with a surface.Change in speed of light between two mediums.
LawsLaw of Reflection (angle of incidence = angle of reflection).Snell’s Law (relates angles to refractive indices).
ApplicationsMirrors, lenses, periscopes.Eyeglasses, camera lenses, prisms for light dispersion.

Conclusion

The phenomena of reflection and refraction are fundamental to our understanding of how light interacts with various mediums and surfaces. These principles have not only enriched our scientific knowledge but have also paved the way for numerous technological advancements that play pivotal roles in our daily lives.

From the vast exploration of the universe through telescopes to the intricate examination of microscopic organisms using microscopes, mirrors have been indispensable tools. They harness the power of reflection to gather and focus light, enabling us to see the unimaginably distant and the infinitesimally small.

FAQ’s

Think of light like a ball. Reflection is like bouncing the ball off a wall. The ball (light) bounces back in the same direction it hit the wall (surface). Refraction is like throwing the ball into a pool. The ball (light) bends as it enters the water (different medium).

  • Reflection: Bouncing back of light upon hitting a surface. (Mirrors!)
  • Refraction: Bending of light as it travels from one medium to another. (Water, lenses!)

Reflection of light is simply the bouncing back of light when it hits a surface. Shiny surfaces like mirrors reflect light well, while rough surfaces scatter it in all directions (diffuse reflection).

In Class 8, you’ll learn the basics of these phenomena. Reflection is when light bounces back, like seeing yourself in a mirror. Refraction is when light bends as it passes through different materials, like a straw appearing bent in a glass of water.

  • Reflection: Light bounces back. (Mirror image)
  • Refraction: Light bends as it enters a different medium. (Straw in water)
  • Diffraction: Light spreads out when it goes around edges or through narrow slits. (Rainbow colors through a prism)
  1. What happens: Reflection – Bounces back. Refraction – Bends.
  2. Surface: Reflection – Can happen on any surface. Refraction – Needs a change in medium (like air to water).
  3. Direction: Reflection – Angle of reflection equals angle of incidence (mirror image). Refraction – Light bends, and the angle depends on the materials involved.

MCQs on Reflection and Refraction

1. Which phenomenon causes light to bounce off a surface without penetrating it?

a) Refraction
b) Diffraction
c) Reflection
d) Dispersion

Answer: c) Reflection

2. What happens to light when it passes from air into water?

a) It speeds up
b) It slows down
c) It bends away from the normal
d) It disappears

Answer: b) It slows down

3. Which type of mirror always forms a virtual and upright image?

a) Concave mirror
b) Convex mirror
c) Plane mirror
d) Spherical mirror

Answer: c) Plane mirror

4. What causes a rainbow to form?

a) Reflection of light
b) Refraction of light
c) Diffraction of light
d) Dispersion of light

Answer: d) Dispersion of light

5. Which lens is used to correct nearsightedness?

a) Concave lens
b) Convex lens
c) Bifocal lens
d) Plano-concave lens

Answer: a) Concave lens

6. In which phenomenon does light spread out as it passes through a narrow slit?

a) Reflection
b) Refraction
c) Diffraction
d) Dispersion

Answer: c) Diffraction

7. What type of mirror is used in a car’s side view mirror?

a) Concave mirror
b) Convex mirror
c) Plane mirror
d) Spherical mirror

Answer: b) Convex mirror

8. What happens to light when it passes from water into air?

a) It speeds up
b) It slows down
c) It bends towards the normal
d) It bends away from the normal

Answer: a) It speeds up

9. Which lens is used in a magnifying glass?

a) Concave lens
b) Convex lens
c) Bifocal lens
d) Plano-concave lens

Answer: b) Convex lens

10. What is the angle of incidence equal to when light undergoes total internal reflection?

a) 90°
b) 0°
c) 180°
d) 45°

Answer: a) 90°

11. Which of the following causes the twinkling of stars?

a) Reflection of light
b) Refraction of light
c) Diffraction of light
d) Dispersion of light

Answer: b) Refraction of light

12. Which mirror can form both real and virtual images?

a) Concave mirror
b) Convex mirror
c) Plane mirror
d) Spherical mirror

Answer: a) Concave mirror

13. What is the bending of light as it passes from one medium to another called?

a) Reflection
b) Refraction
c) Diffraction
d) Dispersion

Answer: b) Refraction

14. Which lens is used in a camera to focus light?

a) Concave lens
b) Convex lens
c) Bifocal lens
d) Plano-concave lens

Answer: b) Convex lens

15. What causes the light to change direction when passing through a prism?

a) Reflection
b) Refraction
c) Diffraction
d) Dispersion

Answer: b) Refraction

16. Which mirror is used by dentists to see a magnified image of a tooth?

a) Concave mirror
b) Convex mirror
c) Plane mirror
d) Spherical mirror

Answer: a) Concave mirror

17. What is the line perpendicular to a surface where light strikes called?

a) Incident ray
b) Refracted ray
c) Normal
d) Angle of incidence

Answer: c) Normal

18. Which lens corrects both nearsightedness and farsightedness?

a) Concave lens
b) Convex lens
c) Bifocal lens
d) Plano-concave lens

Answer: c) Bifocal lens

19. What happens to the speed of light when it enters a denser medium?

a) Increases
b) Decreases
c) Remains the same
d) Stops

Answer: b) Decreases

20. Which phenomenon causes the separation of white light into its component colors?

a) Reflection
b) Refraction
c) Diffraction
d) Dispersion

Answer: d) Dispersion

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