THE ADHYAYAN COACHING CENTER

GAYATRI NAGAR, KUNRAGHAT, GORAKHPUR

CLASS- 10TH (Reflection of light)

Definition of Light:

Light is a form of energy that enables us to see the objects around us. It travels in a straight line and can be reflected,
refracted, or absorbed. Light is part of the electromagnetic spectrum and can travel through a vacuum, such as space.

(Light is the natural agent that stimulates sight and makes things visible.)

Properties of Light

1. Light travels in a straight line.

2. Light is a form of energy.

3. Light can be reflected.

4. Light can be refracted (bent).

5. Light can be absorbed.

6. Light can travel through a vacuum.

7. Light shows wave-particle duality (acts as both wave and particle).

8. Light has a finite speed (approximately 3 × 10⁸ m/s in vacuum).

9. Light causes shadows when blocked.

10. Light enables vision.

Reflection:

Reflection is the bouncing back of light when it strikes a smooth surface like a mirror, without being absorbed.

Types of Reflection:

1. Regular Reflection – Occurs on smooth surfaces (like a mirror), where light rays reflect in a specific direction.

2. Diffuse Reflection – Occurs on rough surfaces, where reflected rays scatter in different directions.

Laws of Reflection

1. First Law: The angle of incidence is equal to the angle of reflection.

2. Second Law: The incident ray, the reflected ray, and the normal to the surface all lie in the same plane.

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Real Image:
A real image is formed when light rays actually meet after reflection or refraction.

• Can be projected onto a screen

• Always inverted (upside down)

• Formed by concave mirrors (when the object is placed beyond the focal point) and convex lenses

Example: Image formed on a cinema screen.

Virtual Image:
A virtual image is formed when light rays appear to meet after reflection or refraction, but they do not actually meet.

• Cannot be projected onto a screen

• Always upright (erect)

• Formed by plane mirrors, convex mirrors, and concave mirrors (when the object is very close to the mirror)

Example: Image you see of yourself in a flat mirror.

Types of Mirror

Plane Mirror Sperical Mirror

1. Cancave
2. convex

Plane Mirror

A plane mirror is a flat, reflective surface that reflects light in a predictable way, producing an image of objects placed in
front of it.

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Image Formation by a Plane Mirror

When an object is placed in front of a plane mirror, light rays from the object reflect off the mirror, and the image is
formed behind the mirror due to the reflection of light.

Key Points About Image Formation:

Property Description

Type of Image Virtual (not real; cannot be captured on a screen)

Orientation Upright (erect)

Size of Image Same size as the object

Lateral Inversion Yes (left and right are reversed)

Distance from Mirror Same as the object’s distance in front of mirror

Position of Image Behind the mirror

Characteristics of a Plane Mirror:

• Flat Surface: Unlike curved mirrors, a plane mirror has a flat reflective surface.

• Image Properties:

o Virtual: The image appears to be behind the mirror and cannot be projected onto a screen.

o Upright: The image maintains the same orientation as the object.

o Laterally Inverted: Left and right appear reversed in the image.

o Same Size: The image is the same size as the object.

o Same Distance: The image appears to be the same distance behind the mirror as the object is in front of
it.

Uses:

• Household mirrors

• Periscopes

• Optical instruments

• Safety and signaling devices

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Concave Mirror:
A concave mirror is a spherical mirror that has a reflecting surface that curves inward, resembling the inside of a sphere.
It is also called a converging mirror because it reflects light inward to one focal point.

Uses of Concave Mirror:

1. Shaving and Makeup Mirrors – Provides a magnified and upright image of the face.

2. Reflecting Telescopes – Used to gather and focus light from distant stars.

3. Headlights of Vehicles – Focuses light into a strong, parallel beam.

4. Solar Concentrators – Concentrates sunlight to a point to generate heat.

5. Dentist’s Mirrors – Allows magnified view of teeth for examination.

6. Microscopes and Projectors – Helps in focusing light onto the specimen or screen.

Convex Mirror:
A convex mirror is a spherical mirror that has a reflecting surface that bulges outward, like the outside of a sphere. It is
also called a diverging mirror because it spreads out light rays that fall on it.

Uses of Convex Mirror:

1. Rear-view Mirrors in Vehicles – Provides a wider field of view to see traffic behind.

2. Security and Surveillance – Used in stores and buildings to monitor large areas.

3. ATM Machines – Helps users see behind for safety.

4. Hallway Corners in Buildings – Prevents collisions by allowing people to see around corners.

5. Road Safety Mirrors – Placed at blind turns to help drivers see oncoming vehicles.

Common Terms for Spherical Mirrors:

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 1. Pole (P):
The center of the mirror’s surface. It is the midpoint of the mirror.

2. Center of Curvature (C):

The center of the sphere from which the mirror is a part. It lies in front of a concave mirror and behind a convex
mirror.

3. Radius of Curvature (R):

The distance between the pole (P) and the center of curvature (C).

4. Principal Axis:
A straight line passing through the pole and the center of curvature of the mirror.

5. Focus (F):
The point on the principal axis where parallel rays of light either meet (concave) or appear to diverge from
(convex) after reflection.

6. Focal Length (f):

The distance between the pole (P) and the focus (F).
It is half the radius of curvature:
𝑅
𝑓=
2
7. Aperture:
The diameter of the reflecting surface of the mirror.

Rules for making ray diagrams by spherical mirror

1. A ray parallel to the principal axis, after reflection, will pass through the principal focus in case of a concave
mirror or appear to diverge from the principal focus in case of a convex mirror.

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 2. A ray passing through the principal focus of a concave mirror or a ray which is directed towards the principal
focus of a convex mirror, after reflection, will emerge parallel to the principal axis.
3. A ray passing through the centre of curvature of a concave mirror or directed in the direction of the centre of
curvature of a convex mirror, after reflection, is reflected back along the same path.
4. A ray incident obliquely to the principal axis, towards a point P (pole of the mirror), on the concave mirror or a
convex mirror, is reflected obliquely. The incident and reflected rays follow the laws of reflection at the point of
incidence (point P), making equal angles with the principal axis.

Ray diagrams for images formed by concave mirror

a. When object is at infinity
1. Image Position − At ‘F’
2. Nature of image – Real, inverted
3. Size – Point sized or highly diminished
b. When object is beyond ‘C’
1. Image Position – Between ‘F’ and ‘C’
2. Nature of image – Real, inverted
3. Size – Diminished
c. When object is at ‘C’
1. Image Position – At ‘C’
2. Nature of image – Real, inverted
3. Size – Same size as that of object

d. When object is placed between ‘F’ and ‘C

1. Image Position – Beyond ‘C’

2. Nature of image– Real, inverted

3. Size – Enlarged

e.When object is placed at’F’

1. Image Position – At Infinity

2. Nature of image – Real, inverted
3.Size – Highly enlarged

f. When object is between ‘P’ and ‘F’

1. Image Position – Behind the mirror

2. Nature of image – Virtual, erect
3. Size – Enlarged

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 Uses of concave mirror
1.Used in torches and flashlights

2.Used in vehicle headlights

3.Used by dentists (dental mirror)

1. Used as shaving or makeup mirrors

2. Used in solar furnaces

3. Used in reflecting telescopes

Ray diagrams of images formed by convex mirror

a. When object is placed at infinity
1. Image Position − At ‘F’
2. Nature of image – Virtual, erect
3. Size – Point sized
b. When object is placed between pole and infinity

1.Image Position – Between ‘P’ and ‘F’

2.Nature of image– Virtual, erect

3.Size – Diminished

Uses of convex mirror

1. Used as rear-view mirrors in vehicles

2. Used in ATMs for security surveillance

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 3. Used in shops and malls for anti-theft monitoring

4. Used at blind turns and road intersections

5. Used in parking lots for wide-angle viewing

Sign Convention for Reflection by Spherical Mirror

(i) The object is placed to the left of the mirror.

(ii) All distances parallel to the principal axis are measured from the pole of the mirror.

(iii) All distances measured in the direction of incident ray (along + X-axis) are taken as positive and those measured
against the direction of incident ray (along – X-axis) are taken as negative.
(iv) Distance measured perpendicular to and above the principal axis are taken as positive.
(v) Distances measured perpendicular to and below the principal axis are taken as negative.

• Object distance = ‘u’ is always negative.

• Focal length of concave mirror = Negative

• Focal length of convex mirror = Positive

𝟏 1 1
Mirror Formula :- = +
𝒇 v u

where, v = Image distance

u = Object distance
f = Focal length

Magnification of Spherical Mirrors

It is the ratio of the height of image to the height of object.

m = Height of image/Height of object

⇒ m = hi/ho
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Also, m = -v/u

→ If ‘m’ is negative, image is real.

→ If ‘m’ is positive, image is virtual.

→ If hi = ho then m = 1, i.e., image is equal to object.

→ If hi > ho then m > 1 i.e., image is enlarged.

→ If hi < ho then m < 1 i.e., image is diminished.

• Magnification of plane mirror is always + 1.

‘+’ sign indicates virtual image.

‘1’ indicates that image is equal to object’s size.

• If ‘m’ is ‘+ve’ and less than 1, it is a convex mirror.

• If ‘m’ is ‘+ve’ and more than 1, it is a concave mirror.

• If ‘m’ is ‘-ve’, it is a concave mirror.

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