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ABHISHEK K RB.Tech - Aerospace, Alliance UniversityCBSE Expert | Inventor of RocketPro6+ Years Teaching Exp | Mentored more than 5000 studentsHelped 1000s of students get 10 CGPA in CBSE X

Focus of Concave & Convex Mirrors

Source: https://gifer.com

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Ray Diagrams of Convex Mirrors

Focus

Sign Convention of Mirrors & Mirror Formula

Refraction and Refractive Index

Standard Incident Rays

Ray Diagrams of Concave Mirrors

Ray Diagrams of Concave & Convex Lenses

Sign Convention of Lenses & Lens Formula

Numericals on Mirrors, Lenses & Refractive Index

Ray Diagrams of Convex Mirrors

Focus

Sign Convention of Mirrors & Mirror Formula

Refraction and Refractive Index

Standard Incident Rays

Ray Diagrams of Concave Mirrors

Ray Diagrams of Concave & Convex Lenses

Sign Convention of Lenses & Lens Formula

Numericals on Mirrors, Lenses & Refractive Index

Convex Mirror Concave Mirror

A B

Q1. A mirror with its reflecting surface curved inwards is called

Plane mirror

C

None of the above

D

Convex Mirror Concave Mirror

A B

Q1. A mirror with its reflecting surface curved inwards is called

Plane mirror

C

None of the above

D

Convex mirror Concave mirror

Plane mirror

None of the above

A B

C D

Q2. If size of the image is not same as size of the object then, it is not a

Convex mirror Concave mirror

Plane mirror

None of the above

A B

C D

Q2. If size of the image is not same as size of the object then, it is not a

PoleCentre of curvature

Principal axis

Aperture

A B

C D

Q3. The entire reflecting area of mirror is called?

PoleCentre of curvature

Principal axis

Aperture

A B

C D

Q3. The entire reflecting area of mirror is called?

ANSWER : Pole

Q6. Midpoint of the aperture of a mirror is called ……..

FOCUS

Let’s consider an incident ray in a concave mirror?

Incident ray

Concave mirror

C

Where would the reflected ray go?

1

2

3

?

??

C

Now let’s apply law of reflection to concave mirror

Incident ray

Concave mirror

C

What is angle of incidence?

Reflected ray & Normal

Incident ray & normal

A B

Angle of incidence is the angle between?

None of theseIncident ray and reflected ray

C D

Reflected ray & Normal

Incident ray & normal

A B

Angle of incidence is the angle between?

None of theseIncident ray and reflected ray

C D

Where is the normal in a concave mirror?

Incident ray

C

Normal of a plane mirror

Plane mirror

Normal

Concave mirror

Let’s draw a normal on a circle.

O

P

Normal is perpendicular to the tangent

P

ONorm

al

Normal passes through the centre

So, we can easily find the direction of the reflected ray

C

B

So, we can easily find the direction of the reflected ray

C

B

BC is the normal

So, we can easily find the direction of the reflected ray

C

Bi

BC is the normal

Measure i

So, we can easily find the direction of the reflected ray

BC is the normal

Measure iDraw r at point B such that i = r

Let’s consider another ray

Let’s consider another ray

The ray passes through the same point on the principal axis

All rays pass through the same point on the principal axis after reflection.

All rays pass through the same point on the principal axis after reflection.

The point is called FOCUS and is denoted by F

F

All the rays converge at one point .

Focus is a point at which rays of light meets after Reflection

Concave mirror → Converging mirror

F

Let’s consider convex mirror

C

Let’s consider convex mirror

Where will the reflected ray go?

C

Let’s consider convex mirror

Where will the reflected ray go?

C

ri

This is the reflected ray

After reflection, they seem to spread out.- (DIVERGE)

Convex mirror → Diverging mirror

C

To an observer it appears that rays are originating from a point behind the mirror.

CF

That is FOCUS in case of a convex mirror

In Concave Mirror Focus is in front of the mirror.

In Convex Mirror Focus is behind the the mirror.

In Concave Mirror Focus is in front of the mirror.

In Convex Mirror Focus is behind the the mirror.

Real Focus

Virtual Focus

Relation between R and F

We Know focus lies on the principal axis.

Concave mirror

CP

F C

Convex mirror

FP

What is the distance between pole and centre of curvature

What is the distance between pole and centre of curvature

Similarly , distance between pole and focus is called Focal length. Denoted by ‘f ‘

Concave mirror

CP

F C

Convex mirror

FP

f f

Focal length is half the radius of curvature

Concave mirror

CP

F C

Convex mirror

FP

f fR R

Focal length is half the radius of curvature

Concave mirror

CP

F C

Convex mirror

FP

f fR R

F= R2

R = 2 F

V I P

Q1. To draw a normal at point S, we should join point S to

P Q

O S

A B

C D

Q1. To draw a normal at point S, we should join point S to

P Q

O S

A B

C D

Q1. To draw a normal at point S, we should join point S to

All the parallel rays meet at the same point after reflection

All the parallel rays converge after reflection

A ray parallel to the principal axis pass through the center of curvature after reflection

All the rays parallel to the principal axis meet at the focus

A

B

C

D

Q2. Which of the statements is not true about a concave mirror?

All the parallel rays meet at the same point after reflection

All the parallel rays converge after reflection

A ray parallel to the principal axis pass through the center of curvature after reflection

All the rays parallel to the principal axis meet at the focus

A

B

C

D

Q2. Which of the statements is not true about a concave mirror?

15 cm 20 cm

10 cm 5 cm

A B

C D

Q3. If focus is located 10 cm from the pole , What is the value of R ?

15 cm 20 cm

10 cm 5 cm

A B

C D

Q3. If focus is located 10 cm from the pole , What is the value of R ?

15 cm 10 cm

30 cm 60 cm

A B

C D

Q4. If the radius of curvature of a convex mirror is 30 cm, What will be the focal length? [Boards 2011]

15 cm 10 cm

30 cm 60 cm

A B

C D

Q4. If the radius of curvature of a convex mirror is 30 cm, What will be the focal length? [Boards 2011]

100 cm Convex mirror

25 cm Convex mirror

25 cm Concave mirror

100 cm Concave mirror

A B

C D

Q5. The outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror. What will be the focal length of this mirror? Which type of spherical mirror will it provide?

[Boards 2010]

100 cm Convex mirror

25 cm Convex mirror

25 cm Concave mirror

100 cm Concave mirror

A B

C D

Q5. The outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror. What will be the focal length of this mirror? Which type of spherical mirror will it provide?

[Boards 2010]

Q6. The point where rays parallel to principal axis meet after reflection is

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