Light Reflection and Refraction Class 10 notes | Light Reflection and Refraction Notes  | Class 10 Light Reflection and Refraction Notes

Topics Covered: (Light Reflection and Refraction Class 10 notes)

• Introduction to Light
  A basic overview of the properties and behavior of light.

• Properties of Light
  Exploring the fundamental characteristics of light waves.

• Reflection of Light

  • Laws of Reflection: The principles governing how light bounces off surfaces.
  • Virtual and Real Images: Differentiating between images formed by various types of mirrors.

Images Formed by Plane Mirrors   in (Light Reflection and Refraction )

Spherical Mirrors

• Characteristics of Concave Mirrors and Convex Mirrors.
• Common terms used when describing spherical mirrors.

Drawing Ray Diagrams for Spherical Mirrors

• Guidelines for constructing ray diagrams to visualize the reflection of light.
• Concave Mirror Image Formation:

• Applications of Concave Mirrors 
  Real-world uses of concave mirrors in various fields.

• Ray Diagrams for Convex Mirrors

• Applications of Convex Mirrors
  Common uses of convex mirrors in daily life.

• Sign Convention for Reflection

• Mirror Equation

• The relationship between object distance, image distance, and focal length, including magnification.

• Reflection from Curved Surfaces: Understanding how light reflects off curved surfaces, specifically spherical mirrors. 

• Introduction to Refraction

• What is Refraction?

• Laws of Refraction

  • Snell's Law: 
  • Refractive Index:
  • Absolute Refractive Index: 
  • Optically Denser Medium: 
  • Optically Rarer Medium: Spherical Lenses

• Convex Lens Image Formation at different place (u)

• Concave Lens Image Formation

• Sign Convention for Spherical Lenses

• Lens Formula

• Magnification by Lenses

• Power of a Lens

Introduction:  (Light Reflection and Refraction Class 10 notes )

• Light is a type of energy that enables us to perceive objects through vision.
• Light is responsible for various observable phenomena such as the formation of images in mirrors, the twinkling of stars, the vibrant colors of a rainbow, the bending of light through different mediums, and more.

Light Reflection and Refraction Class 10 notes | Light Reflection and Refraction Notes  | Class 10 Light Reflection and Refraction Notes

Properties of Light:

• Light is an electromagnetic wave and does not require a medium to propagate.
• It generally travels in a straight line.
• Light exhibits dual characteristics, functioning as both a wave and a particle.
• Light is capable of creating shadows when blocked by an object.
• The speed of light reaches its highest value in a vacuum, which is approximately 3 × 10^8 meters per second.

  When light strikes a surface, one of the following outcomes can occur:

1. Reflection
2. Refraction
3. Absorption

Reflection:

• Reflection is the process where light bounces off a smooth surface, such as a mirror, after hitting it.

Principles of Reflection: 

1. The angle at which light strikes a surface (angle of incidence) is equal to the angle at which it bounces off (angle of reflection).

2. The incident ray, reflected ray, and the normal line at the point of contact all lie in the same flat plane.

Real and Virtual Images: z

An image is formed when two or more light rays either actually converge or seem to converge at a particular location.

Real Image

Produced when light rays actually converge at a specific point.
Can be captured on a screen.
Appears upside down.
Example: Images created on a movie screen or by a concave mirror.

• Virtual Image

  • Formed when light rays seem to meet at a point but don't physically converge.
  • Cannot be displayed on a screen.
  • Appears upright.
  • Example: Images formed by a plane mirror or a convex mirror.

  
  

  Image Created by a Plane Mirror

  • The image formed by a plane mirror is virtual and upright.
  • The image is the same size as the object and appears to be at an equal distance behind the mirror as the object is in front of it.
  • The image is laterally inverted, meaning the left and right sides are swapped.

  
  

Image Created by a Plane Mirror

Features of the Image Formed by a Plane Mirror:

1. The image is virtual and upright.
2. The image size is identical to the object's size.
3. The image appears to be the same distance behind the mirror as the object is in front of it.
4. The image is laterally reversed.

Lateral Reversal: The right side of the object appears on the left side of the image, and vice-versa.

Use of Lateral Inversion:

• The word "AMBULANCE" is written in reverse on the front of vehicles so that it can be correctly read in the rearview mirror of vehicles ahead.

                                                                     

Spherical Mirrors:

• Mirrors that have a curved reflective surface.

• There are two main types of spherical mirrors:

1. Convex Mirror
2. Concave Mirror

Spherical Mirrors:

Characteristics of Concave Mirror:

• The reflective surface is curved inward.
• It is a converging mirror, meaning it brings light rays together.

Characteristics of Convex Mirror:

• The reflective surface is curved outward.
• It is a diverging mirror, meaning it spreads light rays apart.

                                               

Common Terms for Spherical Mirrors:

• Principal Axis: The straight line that connects the pole and the center of curvature.

• Pole (P): The central point of the spherical mirror.

• Aperture (MN): The effective width or diameter of the mirror's reflecting surface.

• Center of Curvature (C): The center of the spherical surface from which the mirror is a segment.

• Radius of Curvature (R): The distance from the pole to the center of curvature.

• Focus (F): The point on the principal axis where parallel rays of light either meet or appear to meet after reflecting off the mirror.

• Focal Length (f): The distance from the pole to the focal point.

• Relation between Focal Length and Radius of Curvature: The focal length is half the radius of curvature, expressed as: f = R/2.

Guidelines for Drawing Ray Diagrams for Spherical Mirrors:

1. A ray traveling parallel to the principal axis will, after reflection, either:
• Pass through the focal point in the case of a concave mirror.
• Appear to diverge from the focal point in the case of a convex mirror.

Light Reflection and Refraction Class 10 notes

2. A ray that passes through the focal point of a concave mirror, or a ray directed towards the focal point of a convex mirror, will reflect and travel parallel to the principal axis.

Light Reflection and Refraction Class 10 notes

3. A ray that passes through the center of curvature of a concave mirror, or is directed towards the center of curvature of a convex mirror, will reflect back along its original path.

Light Reflection and Refraction Class 10 notes

4. A ray that strikes the mirror at an angle, approaching the pole (P) of either a concave or convex mirror, will reflect at an angle as well. The incident and reflected rays will obey the laws of reflection at the point of contact (point P), making equal angles with the principal axis.

Light Reflection and Refraction Class 10 notes

Ray Diagrams for Image Formation by Concave Mirror:

1. When the object is at infinity
• Image Position: At the focal point (F)
• Nature of Image: Real and inverted
• Size: Extremely small or diminished to a point

Light Reflection and Refraction Class 10 notes

2. When the object is beyond the center of curvature (C)
• Image Position: Between the focal point (F) and the center of curvature (C)
• Nature of Image: Real and inverted
• Size: Reduced or smaller in size

Light Reflection and Refraction Class 10 notes

3. When the object is at the center of curvature (C)
• Image Position: At the center of curvature (C)
• Nature of Image: Real and inverted
• Size: Equal to the size of the object

Light Reflection and Refraction Class 10 notes

4. When the object is between the focal point (F) and the center of curvature (C)
• Image Position: Beyond the center of curvature (C)
• Nature of Image: Real and inverted
• Size: Magnified or larger than the object

Light Reflection and Refraction Class 10 notes

5. When the object is at the focal point (F)
• Image Position: At infinity
• Nature of Image: Real and inverted
• Size: Extremely enlarged

6. When the object is between the pole (P) and the focal point (F)
• Image Position: Behind the mirror
• Nature of Image: Virtual and upright
• Size: Enlarged

Light Reflection and Refraction Class 10 notes

Uses of Concave Mirrors:

1. Concave mirrors are used in torches, searchlights, and vehicle headlights to produce a powerful, parallel beam of light.

2. Dentists use concave mirrors to view an enlarged image of a patient's teeth (with the teeth placed between the pole and focus).

3. Concave mirrors are employed as shaving mirrors, allowing a larger view of the face.

4. Large concave mirrors are utilized in solar furnaces to focus sunlight and generate heat.

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Ray Diagrams for Image Formation by Convex Mirror:

1. When the object is at infinity
• Image Position: At the focal point (F)
• Nature of Image: Virtual and upright
• Size: Extremely small or point-sized

2. When the object is placed between the pole and infinity
• Image Position: Between the pole (P) and the focal point (F)
• Nature of Image: Virtual and upright
• Size: Smaller than the object

Uses of Convex Mirrors:

1. Convex mirrors are used as rearview mirrors in vehicles because:

   • They provide an upright, though smaller, image.
   • They offer a broader field of view due to their outward curvature.

2. Convex mirrors are installed at blind corners and intersections to improve visibility of oncoming traffic.

3. They are used as security mirrors in stores to monitor the premises.

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Sign Convention for Reflection by Spherical Mirrors:

1. The object is positioned to the left of the mirror.

2. All distances measured along the principal axis are taken from the pole of the mirror.

3. Distances measured in the direction of the incident ray (along the positive X-axis) are considered positive, while distances measured opposite to the incident ray (along the negative X-axis) are considered negative.

4. Distances measured above the principal axis are positive.

5. Distances measured below the principal axis are negative.

Object Distance and Focal Length:

• The object distance (denoted as ‘u’) is always negative.
• The focal length of a concave mirror is negative.
• The focal length of a convex mirror is positive.

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Mirror Formula:

1/v+1/u=1/f

Where:

• $v$ is the image distance
• $u$ is the object distance
• $f$ is the focal length

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Magnification of Spherical Mirrors:

Magnification is the ratio of the image height to the object height:

m= (Height of Image/ Height of Object) = -v/u

• If $m$ is negative, the image is real.
• If $m$ is positive, the image is virtual.
• If $h_i=ho,$ then $m=1.$ meaning the image is the same size as the object.
• If $,$ then $m>1$indicating the image is enlarged.
• If $h_i<h_o$, then $m<1$, meaning the image is reduced in size.

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Magnification of Plane Mirror:

• The magnification for a plane mirror is always +1.
  • The "+" indicates the image is virtual.
  • The "1" signifies that the image is the same size as the object.

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Magnification for Different Mirrors:

• If $m$ is positive and less than 1, the mirror is convex.
• If $m$ is positive and greater than 1, the mirror is concave.
• If $m$ is negative, the mirror is concave.

Refraction Introduction

• Refraction refers to the change in direction of light as it passes from one transparent medium to another at an angle.

• The speed of light is fastest in a vacuum, where it travels at approximately 3 × 10⁸ meters per second.

• The primary cause of refraction is the alteration in the speed of light as it enters a different medium.

Examples of Refraction

• When looking at a swimming pool, the bottom appears to be at a higher position than it actually is.

• A pencil that is partly submerged in water appears to bend at the point where water and air meet.

• When lemons are placed in a glass tumbler, they seem larger than their actual size.

• When you look at text through a glass slab, the letters seem to be elevated.

Refraction

• The reflection of light occurs when it hits a smooth surface, such as a mirror, and returns to the original medium.

• The amount of bending of light at the two parallel faces of a rectangular glass slab is equal but in opposite directions, causing the ray to exit parallel to the incoming ray.

• The lateral displacement of the light ray is influenced by:

• The refractive index of the glass slab
• The thickness of the glass slab

Here’s the rephrased version of the information:

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Laws of Refraction

1. The incident ray, the refracted ray, and the normal at the point where the light enters the second medium all lie in the same plane.

2. Snell's Law: The ratio of the sine of the angle of incidence to the sine of the angle of refraction remains constant for a particular color of light and for a specific pair of media.
   

   sin ⁡i/sin⁡ r= constant

3. Refractive Index (n): The refractive index of a medium is the ratio of the speed of light in one medium to the speed of light in another medium.
   

   n=(Velocity of light in medium 1) / ( Velocity of light in medium 2)

   • ${\mathrm{<span\; style="font-size:\; large;">n</span>}}_{\mathrm{<span\; style="font-size:\; xx-small;">21</span>}}$ represents the refractive index of medium 2 relative to medium 1:

   • ${\mathrm{<span\; style="font-size:\; large;">n</span>}}_{\mathrm{<span\; style="font-size:\; xx-small;">12</span>}}$ represents the refractive index of medium 1 relative to medium 2:

   • 

1. Absolute Refractive Index: The refractive index of a medium in relation to vacuum or air is called the absolute refractive index.
   

   n=c/ v 

   where $c$ is the speed of light in vacuum ($3 \times 10^8$ m/s).

   • The refractive index of one medium with respect to another is the reciprocal of the other medium's refractive index in the given pair.
     

     n12= 1/ n21

   • If the refractive index of medium 1 with respect to air is $$ ₁n^air and that of medium 2 with respect to air is ₂n^air, then the refractive index of medium 1 with respect to medium 2 is: ₁(₁n^air)/(₁n^air)

2. Refractive Index of Diamond: Diamond has the highest known refractive index, which is 2.42. This means that the speed of light in diamond is 1/2.42 times slower than in vacuum.

3. Optically Denser Medium: The medium with a higher refractive index in a pair of media is considered optically denser.

4. Optically Rarer Medium: The medium with a lower refractive index in a pair of media is considered optically rarer.

• When light travels from a rarer medium to a denser one at an angle, it bends towards the normal line.

• When light moves at an angle from a denser medium to a rarer medium, it refracts away from the normal line.

• The refractive index of a medium is not influenced by its physical density.

• Spherical Lens: A lens made of transparent material with two surfaces, where one or both surfaces are curved.

• A Convex Lens is thicker at the center and thinner at the edges.
• It is a converging lens, meaning it brings parallel light rays to a single point called the focal point.
• When light passes through a convex lens, the rays converge and can form a real or virtual image, depending on the position of the object.
• Commonly used in magnifying glasses, eyeglasses for farsightedness, and cameras.

A Concave Lens is thinner at the center and thicker at the edges.

It is a diverging lens, meaning it spreads out parallel light rays that pass through it.

When light passes through a concave lens, the rays diverge and appear to originate from a common point called the virtual focal point, which is on the same side as the object.

Concave lenses are commonly used in devices like eyeglasses for nearsightedness and in some optical instruments.        

The image formation by convex lens

(i) A light ray traveling parallel to the principal axis of a convex lens will always pass through the focal point on the opposite side of the lens.

(ii) A light ray that passes through the focal point of a convex lens will refract and travel parallel to the principal axis.

iii) A light ray passing through the optical center of the lens will continue in the same direction without any change in its path.

Here’s a reworded version of the ray diagram description for when the object is at infinity:

(i) When the object is at infinity

• Image Position: Located at the focal point (F₂)
• Nature of Image: Real and inverted
• Size of Image: Extremely small or point-sized

Here’s a reworded version of the description for when the object is beyond '2F1':

(ii) When the object is beyond '2F₁'

• Image Position: Between the focal point (F₂) and twice the focal length (2F₂)
• Nature of Image: Real and inverted
• Size of Image: Smaller than the object

Here’s a reworded version for when the object is at ‘2F₁’:

(iii) When the object is at '2F₁'

• Image Position: At '2F₂'
• Nature of Image: Real and inverted
• Size of Image: Same as the object

Here’s a reworded version for when the object is between ‘F₁’ and ‘2F₁’:

(iv) When the object is between 'F₁' and '2F₁'

• Image Position: Beyond '2F₂'
• Nature of Image: Real and inverted
• Size of Image: Magnified

Here’s a reworded version for when the object is at ‘F₁’:

(v) When the object is at 'F₁'

• Image Position: At infinity
• Nature of Image: Real and inverted
• Size of Image: Extremely magnified

(vi) When the object is between 'F₁' and the optical center

• Image Position: On the same side of the lens as the object
• Nature of Image: Virtual and upright
• Size of Image: Magnified

Here’s a reworded version for the rule of image formation by a concave lens:

(i) A light ray parallel to the principal axis seems to originate from the focal point on the same side of the lens.

(ii) A light ray that appears to converge at the focal point of a concave lens will refract and travel parallel to the principal axis. 

(iii) A light ray passing through the optical center of the lens will continue in the same direction without any change in its path.

Here’s a reworded version for the ray diagram of images formed by a concave lens when the object is at infinity:

(i) When the object is at infinity

• Image Position: At the focal point (F₁)
• Nature of Image: Virtual and upright
• Size of Image: Extremely small or point-sized 

(ii) When object is placed between infinity and optical centre

Image Position – Between ‘F’ and ‘O’

Nature of image – Virtual, erect

Size – Diminished  

Sign Convention for Spherical Lenses

• The sign conventions used for spherical lenses are similar to those used for spherical mirrors, but measurements are taken from the optical center of the lens.

• Focal Length:

  • For a convex lens, the focal length is positive.
  • For a concave lens, the focal length is negative.

Lens Formula

1/v - 1/u=1/f

Where:

• $v$ is the image distance
• $u$ is the object distance
• $f$ is the focal length

Magnification

$$m=\frac{h_{\mathrm{<span\; style="font-size:\; xx-small;">i</span><span\; style="font-size:\; 18px;">/ </span>}}}{h_{\mathrm{<span\; style="font-size:\; xx-small;">o</span>}}}=\frac{\mathrm{v/}}{u}$$

Where:

• $m$ is the magnification
• $h_{\mathrm{<span\; style="font-size:\; xx-small;">i</span><span\; style="font-size:\; 18px;"> </span>}}$and $h_{\mathrm{<span\; style="font-size:\; xx-small;">o</span>}}$ are the heights of the image and the object, respectively.

Power of a Lens

• Definition: The power of a lens is the reciprocal of its focal length, measured in meters.

$$P=\frac{\mathrm{1/}}{\mathrm{f }}$$

• The power of a lens indicates its ability to converge or diverge light rays.

• SI Unit of Power: The unit of power is the dioptre (D), where:

  • 1 D = 1 m⁻¹
  • A lens with a focal length of one meter has a power of 1 dioptre.

• Power of Lenses:

  • For a convex lens, the power is positive.
  • For a concave lens, the power is negative.

• Relationship between Power and Focal Length:

  • The power of a lens is inversely proportional to its focal length, i.e., $P\propto \frac{\mathrm{1/}}{f}$

• Power of Combined Lenses:

  • The total power of a combination of lenses is the sum of the individual powers:
    $P$

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