Image formation - PHYSICS class 10

Image Formation by Concave Mirror

Formation of image depends upon the position of the object. There are six possibilities of the position of object in the case of concave mirror.

• Object at infinity
• Object between infinity and centre of curvature (C)
• Object at centre of curvature (C)
• Object between centre of curvature (C) and Principal focus (F)
• Object at Principal Focus (F)
• Object between Principal Focus (F) and Pole (P)

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  OBJECT AT INFINITY
• Since parallel rays coming from the object converge at principal focus, F of a concave mirror; after reflection. Hence, when the object is at infinity the image will form at F.

Fig: Object at Infinity

Properties of image:

• Point sized
• Highly diminished
• Real and inverted

Object between infinity and Centre of Curvature:

When object is placed between infinity and centre of curvature of a concave mirror the image is formed between centre of curvature (C) and focus (F).

Fig: Object Between Infinity and C

Properties of image:

• Diminished compared to object
• Real and inverted

Object at Centre of Curvature (C):

When the object is placed at centre of curvature (C) of a concave mirror, a real and inverted image is formed at the same position.

Fig: Object at C

Properties of image:

• Same size as object
• Real and inverted

Object between Centre of curvature (C) and Principal Focus (F):

When the object is placed between centre of curvature and principal focus of concave mirror, a real image is formed beyond the centre of curvature (C).

Fig: Object between C and F

Properties of image:

• Larger than object
• Real and inverted

Object at Principal Focus (F):

When the object is placed at principal focus (F) of a concave mirror, a highly enlarged image is formed at infinity.

Fig: Object at F

Properties of image:

• Highly enlarged
• Real and inverted

Object between Principal Focus (F) and Pole (P):

When the object is placed between principal focus and pole of a concave mirror, an enlarged, virtual and erect image is formed behind the mirror.

Fig: Object between F and P

Properties of image:

• Enlarged
• Virtual and erect

Positions of Object and Image in Concave Mirror
Position of Object	Position of Image	Size of Image	Nature of Image
At infinity	At focus	Point sized, highly diminished	Real and inverted
Between infinity and C	Between F and C	Dminished	Real and inverted
At C	At C	Same size	Real and inverted
Between C and F	Beyond C	Enlarged	Real and inverted
At F	At infinity	Highly enlarged	Real and inverted
Between F and P	Behind mirror	Enlarged	Virtual and erect

Reflection : Class 10 Physics part II.

Reflection from spherical mirror:

Reflection of Rays parallel to Principal Axis:

In the case of concave mirror: A Ray parallel to principal axis passes through the principal focus after reflection from a concave mirror.

Fig: Rays parallel to principal axis

Similarly, all parallel rays to the principal axis pass through the principal focus after reflection from a concave mirror. Since, a concave mirror converge the parallel rays after reflection, thus a concave mirror is also known as converging mirror.

In the case of convex mirror: A ray parallel to principal axis appears to diverge from the principal focus after reflecting from the surface of a convex mirror.

Fig: Rays parallel to principal axis

Similarly, all rays parallel to the principal axis of a convex mirror appear to diverge or coming from principal focus after reflection from a convex mirror. Since, a convex mirror diverges the parallel rays after reflection, thus it is also known as diverging mirror.

Reflection of ray passing through the Principal Focus:

In the case of concave mirror: Ray passing through the principal focus goes parallel to principal axis after reflection in the case of concave mirror.

Fig: Ray passing through principal focus

In the case of convex mirror: A ray directed towards principal focus goes parallel to principal axis after reflecting from the surface of a convex mirror.

Fig: Ray through principal focus

Ray passing through the Centre of curvature:

In the case of concave mirror: Ray passing through the centre of curvature returns at the same path after reflecting from the surface of a concave mirror.

Fig: Ray passing through C

In the case of convex mirror: Ray appears to passing through or directed towards the centre of curvature goes parallel to the principal axis after reflecting from the surface of a convex mirror.

Fig: Ray passing through C

Ray incident obliquely to the principal axis:Ray obliquely to the principal axis goes obliquely after reflecting from the pole of the both concave and convex mirror and at the same angle.

Fig: Ray passing obliquely to principal axis

LIGHT CLASS 10 PHYSICS

Light: Reflection

Reflection is one of the unique properties of light. It is the reflection of light, which enables us to see any object.

Reflection: The bouncing back of rays of light from a polished and shiny surface is called reflection or reflection of light. It is similar to bouncing back of a football after colliding with a wall or any hard surface.

Fig: Reflection of Light

Laws of Reflection of light:

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

The angle of incidence is denoted by 'i' and angle of reflection is denoted by 'r'. The law of reflection is applicable to all types of reflecting surface.

Mirror and Reflection of Light:

Mirror is a shiny polished object (glass) which reflects most of the rays of light falling upon it. One side of mirror is polished with suitable material to make the other side reflective.

Types of Image formed by mirrors:

Real Image: Image which is formed in front of the mirror and it can be obtained on a screen is called real image.

Virtual Image: Image which is formed behind the mirror and cannot be obtained on a screen is called virtual image.

Types of Mirror:

Plain Mirror: A mirror having a flat surface is called plane mirror.

Formation of image in plane mirror:

Fig: Image formation in plain mirror

• A plane mirror always forms virtual and erect image.
• The distance of image and that of object is equal from the mirror.
• The image formed by a plane mirror is laterally inverted.

Spherical Mirror

Mirrors having curved reflecting surface are called spherical mirrors. A spherical mirror is a part of a sphere.

Types of Spherical Mirror:

Concave Mirror: Spherical mirror with reflecting surface curved inwards is called concave mirror.

Convex Mirror: Spherical mirror with reflecting surface curved outwards is called convex mirror.

Important terms in the case of spherical mirror:

Fig: Concave Mirror

Pole: The centre of reflecting surface of a spherical mirror is known as Pole. Pole lies on the surface of spherical mirror. Pole is generally represented by ‘P’.

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