HADA INSTITUTE
44/2 Bam Bam complex
Trimurti chouraha, DHAR
9407869501
Chapter-9
Ray Optics and optical instruments
Q. What is reflection? Explain types of reflection
Ans. when an optical ray travels in a medium and collide with plane of another medium and moves
back to its previous medium then this process is called reflection.
There are two types of reflections: -
1. Regular reflection: - for parallel incident optical ray if reflected rays also remain parallel
then this reflection is called regular reflection.
2. Irregular reflection: - for parallel incident optical rays if reflected rays do not remain
parallel than this reflection is called irregular reflection. Generally, this reflection is
produced by rough surfaces.
Q. Write down conceptual definitions related to reflection.
Ans.
,HADA INSTITUTE
44/2 Bam Bam complex
Trimurti chouraha, DHAR
9407869501
1. Incident ray: - An optical ray which travels in a medium and makes collision with the plane of
another medium is called incident ray. In figure IO is incident ray.
2. reflected ray: - An optical ray which moves back in previous medium after collision through the
plane of another medium is called reflected ray. In figure OR is reflected ray.
3. incident point: - point at plane of any other medium on which optical ray incident is called
incident point. In figure O is an incident point.
4. Normal: - Perpendicular drawn on incident point is called normal. In figure ON is normal.
5. Angle of incidence: - angle between incident ray and normal is called incident angle. In figure
∠𝑰𝑶𝑵 = 𝒊 is incident angle.
6. Angle of reflection: - angle between reflected ray and normal is called angle of reflection. In
figure ∠𝑹𝑶𝑵 = 𝒓 is angle of reflection.
Q. Write down laws of reflection.
Ans. Laws of reflection are as follows: -
1. incident angle remains equal to angle of reflection. It means ∠𝒊 = ∠𝒓
2. incident ray, reflected ray and normal lie on the same plane.
Q. for a plane mirror proves that distance of object remains equal to distance of image.
Ans.
,HADA INSTITUTE
44/2 Bam Bam complex
Trimurti chouraha, DHAR
9407869501
An object placed at point O in front of plane mirror an optical ray OB incident on mirror and
reflects in BC direction one more optical ray OA incident perpendicularly on mirror and after
reflection moves back on same path if we stretched both optical rays virtually behind the mirror
then they intersect each other at the point I. therefore image formed at point I
∠𝑶𝑩𝑵 = 𝒊 (incident angle)
∠𝑪𝑩𝑵 = 𝒓 (reflected angle)
Therefore, ∠𝑶𝑩𝑵 = ∠𝑪𝑩𝑵
Therefore, ∠𝑶𝑩𝑨 = ∠𝑪𝑩𝑴𝟐 ………… (1)
∠𝑪𝑩𝑴𝟐 = ∠𝑰𝑩𝑨 ………… (2)
Therefore, by equation 1st and 2nd
∠𝑶𝑩𝑨 = ∠𝑰𝑩𝑨
And ∠𝑶𝑨𝑩 = ∠𝑰𝑨𝑩 = 𝟗𝟎𝟎
Therefore, in triangles OAB and IAB
Two angles are equal, and one side AB is common. So, these triangles are congruent triangles.
So, their corresponding sides remain equal. Therefore,
OA = AI
It means distance of object remains equal to distance of image.
Q. What is a spherical mirror. Write down types of spherical mirror.
Ans. spherical mirror is a mirror which is cut off from a hollow sphere and polished at its any
surface.
, HADA INSTITUTE
44/2 Bam Bam complex
Trimurti chouraha, DHAR
9407869501
1. Concave Mirror: - if light reflects from internal surface, then that mirror is called concave
mirror.
2. Convex Mirror: - If light reflects from external surface, then the mirror is called convex
mirror.
Q. Write down conceptual definitions related to spherical mirrors.
Ans.
conceptual definitions related to spherical mirror are as follows: -
1. Pole: - midpoint of spherical mirror is called pole. It is represented by P.
2. Centre of Curvature: - center of sphere from which mirror cut off is called center of
curvature. It is represented by C.
3. Principal axis: - line joins the pole with center of curvature is called principal axis.
4. Radius of curvature: - radius of sphere from which mirror cut off is called radius of
curvature. Or Distance between pole and center of curvature is called radius of curvature.
It is represented by R.
5. Focal point: -
44/2 Bam Bam complex
Trimurti chouraha, DHAR
9407869501
Chapter-9
Ray Optics and optical instruments
Q. What is reflection? Explain types of reflection
Ans. when an optical ray travels in a medium and collide with plane of another medium and moves
back to its previous medium then this process is called reflection.
There are two types of reflections: -
1. Regular reflection: - for parallel incident optical ray if reflected rays also remain parallel
then this reflection is called regular reflection.
2. Irregular reflection: - for parallel incident optical rays if reflected rays do not remain
parallel than this reflection is called irregular reflection. Generally, this reflection is
produced by rough surfaces.
Q. Write down conceptual definitions related to reflection.
Ans.
,HADA INSTITUTE
44/2 Bam Bam complex
Trimurti chouraha, DHAR
9407869501
1. Incident ray: - An optical ray which travels in a medium and makes collision with the plane of
another medium is called incident ray. In figure IO is incident ray.
2. reflected ray: - An optical ray which moves back in previous medium after collision through the
plane of another medium is called reflected ray. In figure OR is reflected ray.
3. incident point: - point at plane of any other medium on which optical ray incident is called
incident point. In figure O is an incident point.
4. Normal: - Perpendicular drawn on incident point is called normal. In figure ON is normal.
5. Angle of incidence: - angle between incident ray and normal is called incident angle. In figure
∠𝑰𝑶𝑵 = 𝒊 is incident angle.
6. Angle of reflection: - angle between reflected ray and normal is called angle of reflection. In
figure ∠𝑹𝑶𝑵 = 𝒓 is angle of reflection.
Q. Write down laws of reflection.
Ans. Laws of reflection are as follows: -
1. incident angle remains equal to angle of reflection. It means ∠𝒊 = ∠𝒓
2. incident ray, reflected ray and normal lie on the same plane.
Q. for a plane mirror proves that distance of object remains equal to distance of image.
Ans.
,HADA INSTITUTE
44/2 Bam Bam complex
Trimurti chouraha, DHAR
9407869501
An object placed at point O in front of plane mirror an optical ray OB incident on mirror and
reflects in BC direction one more optical ray OA incident perpendicularly on mirror and after
reflection moves back on same path if we stretched both optical rays virtually behind the mirror
then they intersect each other at the point I. therefore image formed at point I
∠𝑶𝑩𝑵 = 𝒊 (incident angle)
∠𝑪𝑩𝑵 = 𝒓 (reflected angle)
Therefore, ∠𝑶𝑩𝑵 = ∠𝑪𝑩𝑵
Therefore, ∠𝑶𝑩𝑨 = ∠𝑪𝑩𝑴𝟐 ………… (1)
∠𝑪𝑩𝑴𝟐 = ∠𝑰𝑩𝑨 ………… (2)
Therefore, by equation 1st and 2nd
∠𝑶𝑩𝑨 = ∠𝑰𝑩𝑨
And ∠𝑶𝑨𝑩 = ∠𝑰𝑨𝑩 = 𝟗𝟎𝟎
Therefore, in triangles OAB and IAB
Two angles are equal, and one side AB is common. So, these triangles are congruent triangles.
So, their corresponding sides remain equal. Therefore,
OA = AI
It means distance of object remains equal to distance of image.
Q. What is a spherical mirror. Write down types of spherical mirror.
Ans. spherical mirror is a mirror which is cut off from a hollow sphere and polished at its any
surface.
, HADA INSTITUTE
44/2 Bam Bam complex
Trimurti chouraha, DHAR
9407869501
1. Concave Mirror: - if light reflects from internal surface, then that mirror is called concave
mirror.
2. Convex Mirror: - If light reflects from external surface, then the mirror is called convex
mirror.
Q. Write down conceptual definitions related to spherical mirrors.
Ans.
conceptual definitions related to spherical mirror are as follows: -
1. Pole: - midpoint of spherical mirror is called pole. It is represented by P.
2. Centre of Curvature: - center of sphere from which mirror cut off is called center of
curvature. It is represented by C.
3. Principal axis: - line joins the pole with center of curvature is called principal axis.
4. Radius of curvature: - radius of sphere from which mirror cut off is called radius of
curvature. Or Distance between pole and center of curvature is called radius of curvature.
It is represented by R.
5. Focal point: -
