Light Mirrors and Lenses Class 8 Notes Science Chapter 10

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Class 8 Science Chapter 10 Light Mirrors and Lenses Notes

Class 8 Science Curiosity Chapter 10 Notes

Class 8 Science Chapter 10 Notes – Light Mirrors and Lenses Notes Class 8

→ Reflection of light The phenomenon of change in the direction of light or the bouncing back of light when it falls a on shiny polished surface or mirror.

→ Convex mirror A spherical mirror where the reflective surface bulges outward towards the light source, e.g. Rear-view mirror of a car.

→ Concave mirror A spherical mirror where the reflecting surface is on the inner side of curved shape, e.g. Shaving mirror.

→ Real image An image that can be formed on a screen.

→ Virtual image An image that cannot be formed on the screen.

→ Convex lens A lens that is thicker at the centre and thinner at the edges.

→ Concave lens A lens that is thinner at the centre and thicker at the edges.

→ Lateral inversion The phenomenon in which the left and right sides of an image appear reversed in a plane mirror.

→ A mirror shows your head bigger and body smaller. Which kind of curved mirror might be doing this?

→ Without touching the mirror, how can you tell if it is convex or concave just by looking into it?

→ A roadside mirror lets you see cars coming from behind with a wider view. What kind of mirror makes this possible?

→ You wear a T-shirt with text and notice it looks reversed in the mirror. What causes this?

→ A mirror in your bathroom shows your exact same size and shape. What type of mirror is this?

→ A ray of light returns along the same path after hitting a mirror. What does this tell you about the angle of incidence?

→ Your friend stands in front of a new glass building and sees a perfect image. What type of reflection is happening?

→ A ray of light strikes a plane mirror at an angle of incidence of 350. What is the angle of reflection?

→ An object placed infront of a lens appears upside down on the screen. What does it say about the nature of the image?

→ A convex lens focuses sunlight to a point on paper. What property of the lens allows it to do so?

→ A lens is used in a torch to make the beam straight and focused. Which lens is it?

→ A lens makes parallel rays meet at a point. What type of lens is it?

Spherical Mirror

A spherical mirror is a mirror that has a curved surface instead of a flat one. It looks like a part of a ball and can be curved inward or outward, which changes the way it reflects light and forms images.

We see spherical mirrors in many places around us

1. Used in car mirrors to see the road behind.
2. Found in mirrors used for shaving or applying makeup.
3. Seen in mirrors placed in shops or parking areas for security.

Types of Spherical Mirror

There are two types of spherical mirror
1. Concave Mirror
A spherical mirror where the reflecting surface is on the inner side of the curved shape is called concave mirror.
e.g. Shaving mirror.

Image Formed by a Concave Mirror

• If the object is far away from the mirror, the image formed is real, inverted (opposite side up as the object) and diminished (smaller than the object).
• If the object is very close from the mirror, the image formed is virtual, erect (same side up as the object) and enlarged (larger than the object).

Uses of Concave Mirrors

• Concave mirrors are used by dentist to see the large image of teeth.
• Concave mirrors are used as reflectors in torches, headlights of vehicles and searchlights, etc., to get a strong and straight beam of light.
• Concave mirrors are used as shaving mirrors to see a large image of face.

2. Convex Mirror
A spherical mirror where the reflecting surface is on the outer side of the curved shape is called convex mirror, e.g. Rear view mirror of a car.

As the front side (or inner side) of a spoon is bent inward, so the front side of a shining spoon represents a concave mirror, while the back side (or outer side) of a spoon is bulging outward, so the back side of a shining spoon represents a convex mirror as shown in figure.

Image Formed by a Convex Mirror
• A convex mirror always forms a virtual, erect and diminished image of object.

Uses of Convex Mirrors

• To see the wide area of traffic at the rear side or backside on the road, convex mirrors are used as rear view mirrors or side view mirrors in vehicles such as cars, scooters, buses, etc.

convex mirror as rear view mirror

• Big convex mirrors are used as shop security mirrors.

Formation of Spherical Mirrors

• A spherical mirror is like a small part of a hollow sphere.
• It is made by shaping and polishing a curved glass piece.
• A thin reflective coating (like aluminium) is added to one side.

• If the coating is on the outer surface, the inner surface reflects concave mirror.
• If the coating is on the inner surface, the outer surface reflects convex mirror.
• The reflecting side is the shiny, uncoated surface.

Difference between concave and convex mirrors

Features	Concave mirror	Convex mirror
Shape	Curved inward (like the inside of a spoon)	Curved outward (like the back of a spoon)
Reflecting side	Shiny side is on the inside	Shiny side is on the outside
Image formed	Can be big, small, straight or upside down	Image is always small and straight
View area	Shows a small area	Shows a large area
Diagram

Images formed by Different Mirrors

Concave Mirror

1. When the object is close the image is erect and enlarged
2. When the object is far the image becomes inverted and smaller.
3. Image size changes clearly with distance.
4. It is used in shaving mirrors, dentist tools, solar cookers.

Convex Mirror

1. When the object is close the image is erect and smaller.
2. When the object is far the image remains erect and becomes slightly smaller.
3. Image size change is slight
4. It is used in car mirrors, shop security mirrors.

Plane Mirror

1. Image is always erect and same size, whether the object is close or far.
2. No change in image size.
3. It is used in homes and dressing rooms to see a clear, erect image of ourselves.

Lateral Inversion

Lateral inversion is the effect seen in a mirror where the left side appears as right and the right side appears as left.
For example, if you raise your right hand, it looks like the left hand in the mirror.

• Lateral inversion (left-right reversal) is clearly seen in plane mirror. It also occurs in convex mirror but is not clearly seen in concave mirrors.

Reflection

When light strikes a smooth and shiny surface, like a mirror, it comes back in the same direction. This phenomenon is known as the reflection of light.
It helps us see images in mirrors.

Key Terms Related to Reflection of Light

1. Incident Ray : The ray of light (AO) that falls on the surface (like a mirror).
2. Reflected Ray : he ray of light (OB) that bounces off the reflecting surface after striking it.
3. Point of Incidence : The exact point O on the reflecting surface where the incident ray strikes.
4. Normal : An imaginary line perpendicular to the reflecting surface at the point of incidence.
5. Angle of Incidence (∠i) : The angle between the incident ray and the normal.
6. Angle of Reflection(∠r) : The angle between the reflected ray and the normal.

Laws of Reflection
When light reflects from a smooth surface like a mirror, it follows certain rules. These rules are called the laws of reflection.

1. First Law The incident ray, the reflected ray and the normal to the surface all lie in the same plane.
2. Second Law The angle of incidence is equal to the angle of reflection. (∠i = ∠r)

Types of Reflection by Different Mirror

Different mirrors reflect light in different ways. A plane mirror, a concave mirror, and a convex mirror all change the way light reflect and because of this, the image formed by each mirror also looks different.

Regular Reflection (Plane Mirror) Regular reflection happens when light falls on a smooth and shiny surface, like a plane mirror, and rays reflect in the same direction.
Forms a clear, sharp image.

Converging Reflection (Concave Mirror) Converging reflection is a type of reflection in which light rays reflect and converge (meet) at a single point.

This happens in concave mirrors, where the reflected rays come together tp form a bright and focused image. It is useful in devices like shaving mirror torches, headlights, and solar cookers.

Diverging Reflection (Convex Mirror) Diverging reflection is a type of reflection in which light rays spread out after reflecting from a surface.

This happens in convex mirrors, where the reflected rays move away from each other. It helps to give a wider view and is used in vehicle side mirrors and security mirrors.

Solar concentrators use mirrors/lenses to focus sunlight into intense heat. This heat boil liquid for steam power or directly melts/cooks materials at very high temperatures.

Lens

A lens is a transparent object made of glass or plastic that is curved on one or both sides. It bends light rays and helps to form images.
There are two main types of lenses, convex lens and concave lens.

1. Convex Lens
A spherical lens which is thicker at the centre and thinner at the edges is known as convex lens. e.g. Magnifying glass, microscopes.

Convex Lens

2. Concave Lens
A spherical lens which is thinner at the centre than at the edges is called concave lens. e.g. peep-holes in the door, spectacles etc.

Concave Lens

Comparison of Convex and Concave Lenses

Feature	Convex Lens	Concave Lens
Shape	Thicker in the middle, thinner at the edges	Thinner in the middle, thicker at the edges.
Light Behavior	Converges (brings together) light rays	Diverges (spreads out) light rays
Image Formation	Can form real or virtual image	Always forms virtual, erect and smaller image

Applications of Convex and Concave Lens

Convex Lens

1. Helps people with farsightedness see nearby objects clearly.
2. Magnify small objects in device like a magnifying glass.
3. Bring distant objects into focus in a telescope.

Concave Lens

1. Correct nearsightedness by helping people see far object clearly.
2. Helps in diverging light rays before they enter a convex lens in optical devices.
3. Widens the view in peepholes and flashlight by spreading light.