1. Light-Reflection and Refraction
Q.1 Define light. What is its nature?
Ans. Light:- light is a form of energy which causes in us the sensation of sight. Light travels in a straight line path but when the size of an opaque object becomes very small, it has a tendency to bend around it.
Light has a dual nature i.e. wave nature as well as particle nature.
Q.2 What is a plane mirror? What are the characteristics of an image formed in a plane mirror?
Ans. Plane Mirror:- A thin, flat and smooth sheet of glass having coating of silver metal on one side is called a plane mirror. The silver coating is protected by a red paint. E.g. the mirror in our homes in which we see our face is a plane mirror.
Characteristics of a Plane Mirror:-
1. The image formed in a plane mirror is always virtual.
2. The image formed in a plane mirror is always erect.
3. The size of image formed in a plane mirror is always same as that of the object
4. The image formed in a plane mirror is at the same distance behind the mirror as the object is in front of it.
5. The image formed in a plane mirror is laterally inverted (or sideways reversed).
Uses of plane mirror:–
I. Plane mirrors are used to see ourselves.
ii. These are fitted on the inside walls of certain shops (like jewellery shops) to make them look bigger.
iii. These are fitted at blind turns of some busy roads to see the vehicles coming from the other side.
iv. Plane mirrors are used in making periscopes.
Q.3 What is meant by reflection of light? What are the laws of reflection of light?
Ans. Reflection of light:– When a beam of light is incident on a plane surface, a part of it is returned back into the same medium. This process of sending back of light rays which falls on the surface of an object is called reflection of light.
Laws of Reflection:- The reflection of light from a plane surface or from a spherical surface takes place according to two laws which are known as laws of reflection. There are two laws of reflection as:
1. Ist Law:- It states that, “The incident ray, the reflected ray and the normal all lie in the same plane at the point of incidence”.
e.g. In fig. the incident ray, the reflected ray and the normal all lie in the same plane of paper. Neither of the two rays or normal goes down into the paper or comes out of the paper.
2. 2nd Law:- It states that ,”The angle of incidence is always equal to the angle of reflection”.
e.g. If ∟PON = ∟i is the angle of incidence
and ∟QON = ∟r is the angle of reflection,
then,
∟i = ∟r
Q.4 What is an image? What are real and inverted images?
Ans. Image:- The optical appearance produced when light rays coming from an object are reflected from the mirror (or refracted from the lens) is known as image.
e.g. When we look into a mirror, we see the image of our face.
Images are of two types as:
a. Real Images:- Those images which can be projected on a screen are called real images.
e.g. The images of actors or actresses projected on a cinema screen are real images.
b. Virtual Images:- Those images which cannot be projected on a screen are called virtual images.
e.g. The image of our face in a plane mirror cannot be obtained on a screen, so it is a virtual image.
Q.5 Distinguish between real and virtual images.
Ans.
|
Real Image |
Virtual Image |
|
1 These images can be projected on a screen. 2. These are formed when reflected rays (or refracted rays) actually meets.
3. These are always inverted. |
1. These images cannot be projected on a screen. 2. These are formed when reflected rays (or refracted rays) appears to meet. 3. These are always erect. |
Q.6 What is a spherical mirror? What are its types?
Ans. Spherical Mirror:- A spherical mirror is a surface forming part of hollow sphere of glass whose one side is coated with silver, so that reflection takes place from the other side.
Spherical mirrors are of two types as:
I. Concave mirror.
II. Convex mirror.
I. Concave mirror:- A spherical mirror is said to be concave, if it is silvered on outer curved surface and the reflection takes place from the inner hallow surface.
e.g. The inner bent side of a shining spoon is an example of a concave mirror.
This type of mirror is also known as converging mirror.
II. Convex Mirror:- A spherical mirror is said to be convex, if it is silvered on inner hallow surface and the reflection takes place from the outer curved surface.
e.g. back side of shining spoon is an example of a convex mirror.
This type of mirror is also known as diverging mirror.
Q.7 Define the following terms with reference of a spherical mirror:
i. Pole ii. Centre of curvature iii. Radius of curvature iv. Principal axis
v.Aperture.
Ans.
i. Pole:- The mid point (P) of the reflecting surface of a spherical mirror is called pole of the mirror and is denoted by ‘P’.
ii. Centre of Curvature:- The centre of hollow sphere of glass of which mirror is a part is called centre of curvature. It is denoted by ‘C’
iii. Radius of curvature:- The radius of hollow sphere of glass of which a mirror is a part is known as radius of curvature. It is denoted by ‘R’.
iv. Principal axis:- The straight line passing through the centre of curvature (C) and pole (P) of a spherical mirror is called principal axis.
v. Aperture:- That portion of a spherical mirror from which the reflection of light takes place is called the aperture of the mirror.
Q.8 Define principal focus and focal length of a spherical mirror.
Ans.
Principal Focus:- The point where a beam of light coming parallel to principal axis actually converges (in case of a concave mirror) or appears to diverge from (in case of a convex mirror) after reflection from the spherical mirror on the principal axis is called principal focus or focus of the mirror.
Focal Length:– The distance between the principal focus and the pole of the mirror is called the focal length. It is denoted by ‘f’.
Q.9 Prove that the focal length of a spherical mirror is the half the radius of curvature.
OR
Derive the relationship between focal length and radius of curvature of a spherical mirror.
Ans. Take a mirror ‘MM`’ and consider a ray of light AB parallel to principal axis, falling on the mirror at B. The ray after reflection passes through the focus ‘F’.
Join B and centre of curvature. Let CB be the normal on the mirror at B.
Now, according to 2nd law of reflection:
Angle of incidence = Angle of reflection
ð∟ABC = ∟CBF …………….(1)
Also ∟ABC = ∟BCF …………….(2) (Alt. int. angles)
From (1) and (2), we get
∟CBF = ∟BCF
ð∆BCF isosceles
ðCF = BF ……………………(3)
Now, if the aperture of the mirror is very small, point B lies very close to the pole ‘P’ then
PF = BF ……………………….(4)
From (3) and (4), we get
PF = CF
Since, PC = PF + CF
ðPC = PF = PF (.: PF = CF)
ðPC = 2PF
ðR = 2f
ðF = R/2
Hence, focal length is half the radius of curvature.
Q.10 State the rules for obtaining images formed by concave mirrors.
Ans. An image is formed at that point where at least two reflected rays meets or appears to meet.
For concave mirrors, following rules are used:
Rule 1st:- A ray of light which is parallel to the principal axis of a concave mirror, passes through its focus after reflection from the mirror.
Rule 2nd:- A ray of light passing through the centre of curvature of a concave mirror is reflected back along the same path.
Rule 3rd:- A ray of light passing through the focus of a concave mirror becomes parallel to the principal axis after reflection.
Rule 4th:- A ray of light which is incident at the pole of a concave mirror is reflected back making the same angle with the principal axis.
Q.11 With the help of diagrams, discuss the position, nature and size of the images formed by a concave mirror?
Ans.The nature, position and size of an image formed by a concave mirror depends upon the its distance from the mirror. An object can be placed at the following positions:
1. Between pole (P) and Focus (F):- when an object is placed between the pole (P) and focus (F) of a concave mirror, the image formed is:
a. behind the mirror
b. virtual and erect
c. highly magnified
2. At Focus (F):- When the object (AB) is placed at the focus of a concave mirror, the image formed is:
a. at infinity
b. real and inverted
c. highly magnified
3. Between focus (F) and centre of curvature(C):- When the object is placed between the focus and the centre of curvature, the image formed is:
a. beyond the centre of curvature
b. real and inverted
c. larger than the object
4. At the centre of curvature (c):- When the object is placed at the centre of curvature (C), the image formed is:
a. at the centre of curvature
b. real and inverted
c. same size as the object
5. Beyond the centre of curvature:- When the object is placed beyond the centre of curvature, the image formed is:
a. between focus (F) and centre of curvature
b. real and inverted
c. diminished
6. At infinity:- When the object is placed at infinity, the image formed is:
a. at focus (F)
b. real and inverted
c. highly diminished
Q.12 List some uses of a concave mirror.
Ans. Uses of a concave mirror:- Some important uses of a concave mirror are as:
i. Concave mirrors are used as shaving mirrors because these can form erect and magnified image of the face.
ii. These are used as reflectors in torches, vehicle head lights and search lights to powerful beam of light.
iii. These are used by doctors to concentrate light on body parts like ears and eyes which are to be examined.
iv. These are used by dentists to observe large images of teeth of patients.
v. Large concave mirrors are used in solar heating devices like solar cookers, solar furnaces etc.
vi. Large concave mirrors are used in reflecting type telescopes.
Q.13 State the rules for obtaining images formed by convex mirrors.
Ans. Rules for convex mirrors:- These are as:
Rule 1st:- A ray of light which is parallel to the principal axis of a convex mirror appears to be coming from its focus after reflection.
Rule 2nd:- A ray of light going towards the centre of curvature of a convex mirror is reflected back along the same path.
Rule 3rd:- A ray of light which is going towards the focus of a convex mirror becomes parallel to the principal axis after reflection.
Rule 4th:- A ray of light which is incident at the pole of a convex mirror is reflected back making the same angle with the principal axis.
Q.14 Discuss the position, nature and size of the image formed by a convex mirror.
Ans. In case of a convex mirror, an object can be placed at the following two main positions:
1. Anywhere between pole (P) and infinity:- When the object is placed anywhere between pole and infinity, the image formed is:
a. behind the mirror between pole and focus
b. virtual and erect
c. diminished
2. At infinity:- when the object is at infinity, the image formed is:
a. behind the mirror at focus
b. virtual and erect
c. highly diminished.
Q.15 List some uses of convex mirrors.
Ans. Uses of convex mirrors:- are as:
i. A convex mirror is used as a reflector in street lamps as it diverges light over a large area.
ii. A convex mirror is used as a rear view mirror in vehicles to see the traffic behind.
Q.16 Why does a driver prefer to use a convex mirror as a back view mirror in automobiles?
Ans. A driver prefers to use a convex mirror as a rear view mirror because:
a. it always produces an erect image.
b. the image formed is very diminished due to which it gives a wide field of view.
Q.17 What are the New Cartesian Sign Conventions for spherical mirrors?
Ans. New Cartesian Sign Conventions:- New Cartesian sign conventions are used for measuring various distances in the ray-diagram of spherical mirrors.
According to new Cartesian conventions:
i. All the distances are measured from the pole as origin.
ii. The distances measured in the same direction as that of incident light are taken as positive.
iii. The distances measured against the direction of incident light are taken as negative.
iv. Heights measured in upwards and perpendicular to the principal axis are taken as positive.
v. Heights measured in downwards and perpendicular to the principal axis are taken as negative.
Generally, the direction of incident ray of light is taken from left to right. In such a case, the distances measured from pole to the right is positive and to the left is negative.
Conclusions:-
1. An object is always placed to the left side of the mirror. Thus, the object distance (u) is always negative.
2. The image formed by a concave mirror can be either behind the mirror or in front of it. So, the image distance (v) for a concave mirror can either be positive or negative and vice versa.
3. In case of a convex mirror, the image is always formed on the right side. So, the image distance (v) for a convex mirror is always positive.
4. The focal length of a concave mirror is always negative while that of a concave mirror is always is always positive.
5. The object is always placed above the principal axis and in the upward direction. So, the object height (h1) is always positive.
6. If the image is formed above the principal axis, then it is taken as positive while if it is formed below the principal axis then, it is taken as negative.
Q.18 What is a mirror formula?
Ans. Mirror Formula:- A formula which gives us a relationship between image distance (v), object distance (u) and focal length (f) of a mirror is called a mirror formula.
According to mirror formula:
1v+1u=1f
While applying this formula, it should be noted that ‘u’ is always negative for both concave and convex mirrors, ‘f’ of a concave mirror is taken as negative while that of a convex mirror is taken as positive. If the image is real i.e. on the same side of the mirror ‘v’ is negative and if the image is virtual i.e. behind the mirror, ‘v’ is positive.
Q.19 What do you mean by linear magnification?
Ans. Linear Magnification:- The ratio of the height of image to the height of object is known as linear magnification. It is denoted by ‘m’.
i.e. Linear Magnification = Height of image
Height of object
ðm=h2h1
Where h2 = height of object
And h1 = height of image.
Linear magnification is also defined as the ratio of the image distance to the object distance with a negative sign.
i.e. Linear magnification=
–Image distanceobject distance
=> m= –vu
Note:- The sign of ‘m’ will be determined always by the signs of h1, h2 ,v and u.
Problem 1. An object is placed at 60 cm from a concave mirror of focal length 20 cm. find the position and nature of the image formed.
Sol.
Here, object distance (u) = -60 cm
Focal length (f) = – 20 cm
Let image distance = v cm.
Now, we know that
1v+1u=1f
ð1v+1(-60)=1-20
ð1v=1-20+160
ð1v= 60-20-1200
ð1v=40-1200
ð1v=1-30
ðV = -30 cm.
Thus, the image is formed in front of mirror and its nature is real and inverted.
Problem 2. A concave mirror produces 3 times magnified real image of an object placed at a distance of 10 cm in front of it. Where is the image located?
Sol.
Here, magnification (m) = -3
Object distance (u) = -10 cm
Image distance (v) = ?
We know that
m= –vu
ð-3= –v-10
ð-3=v10
ðv= -30 cm
Hence, the image is located at a distance of 30 cm in front of the mirror.
Problem 3. Find the focal length of a convex mirror of radius of curvature 1m.
Sol.
Here, focal length (f) = ?
Radius of curvature (R) = +1m
We know that
f=R2
ðf=12 m
Or f=0.5 m
Q.20 What do you mean by refraction of light? State the laws of refraction of light?
Ans. Refraction of light:- When a ray of light travels from one transparent medium to another, it bends from its original path at the boundary of separation. This phenomenon of bending of light when it travels from one transparent medium into another medium is called refraction of light.
e.g. The refraction of light takes place when the light enters from air into glass or vice versa.
Cause of Refraction:- The basic cause of refraction of light is the change in speed of light in going from one medium into another medium. E.g. When a ray of light enter from air into glass, the speed of light decreases and vice versa.
Laws of Refraction:- The refraction of light on going from one medium into another medium takes place according to two laws which are known as laws of refraction of light. These are as:
Ist Law:- It states that, “The incident ray, the refracted ray and the normal to the surface of separation of the media, all lie in the same plane.”
e.g. In fig. the incident ray, the refracted ray and the normal all lie in the same plane of paper.
2nd Law:- It states that, “The ratio of sine of angle o incidence to the sine of angle of refraction is constant for a given pair of media.”
i.e. Sine
of angle of
incidenc��Sine of
angle of refraction=Constant
=> SiniSinr=n
Where ‘n’ is a constant and is known as refractive index.
The second law of refraction of light was discovered by Snell experimentally in 1621, so it is also known as Snell’s law of refraction.
Q.21 Explain the refraction of light through a glass slab.
Ans. Refraction through a glass slab:- Consider a glass slab PQRS as shown n fig. Here, we have two media, air medium (rear medium) and glass medium (denser medium). Now, let a ray of light AO travelling in air is incident on the glass slab at the point ‘O’. As the glass slab is transparent, most of the incident light passes into it. Since glass slab is an optically denser medium than air, so when the ray of light AO passes from air into glass, its direction changes and goes along the path OO`. In this way, the refraction of light or bending f light takes place in the glass slab.
Q.23 Define rarer and denser media.
Ans. A transparent substance in which light travels is known as a medium. E.g. air, glass, water, etc.
Rarer Medium:- A medium in which the speed of light is more is known as optically rarer medium. E.g. Air (speed of light = 3×108 m/sec) is optically rarer medium as compared to glass (speed of light = 2×108 m/sec)
Denser Medium:- A medium in which the speed of light is less is known as optically denser medium. E.g. Water (speed of light = 2.25×108 m/sec) is optically denser than air.
NOTE:- It has been found that:
i. when a ray of light goes from rarer medium to denser medium, it bends towards the normal.
ii. When a ray of light goes from denser medium to rarer medium, it bends away from normal.
Q.23 What are the necessary conditions for no refraction?
Ans. Conditions for no refraction:- No refraction takes place:
i. Light ray falls normally (perpendicularly) to the surface of separation.
ii. The refractive indices of two media are equal.
Q.24 Define refractive index. What is its unit?
Ans. Refractive Index:- The refractive index is defined as the ratio of the speed of light in vacuum to the speed of light in a given medium.
It is generally denoted by ‘n’.
i.e. Refractive Index=
speed of
light in air(or
vacuum)speed
of light
in a given
medium
=> n=cv
Where, C = 3×108 m/sec. is the speed of light in air or vacuum.
Refractive index has no units.
Q.25 The refractive index of diamond is 2.42. What does that mean?
Ans. By saying that the refractive index of diamond is 2.42, it means that the ratio of the speed of light in air (or vacuum) to the speed of light in diamond is 2.42.
Problem 4. Speed of light in glass is 2×108 m/sec. Calculate its refractive index?
Sol.
Here, speed of light in glass (v) = 2×108 m/sec.
Now, we know that
Refractive index, n=CV
ðn=3×108
m/sec2×108 m/sec
ðn=32
ðn=1.5
Hence, refractive index of glass is 1.5
Problem 5: Calculate the refractive index of air, if the speed of light in air is 2.9970×108 m/sec and that in vacuum is 2.9979×108 m/sec.
Ans. Try yourself Ans. 1.0003
Q.26 Explain why a stick when partially immersed in water appears to be bent?
Ans. When a stick ABO is partially immersed in water and held obliquely to the surface, it appears bent due to the refraction of light.
Let O be the lower end point of the stick immersed in water and also let two rays OC and OD coming from ‘O’ in water in straight line paths until they reach the surface of water. When the ray of light ‘OC’ enters into air, it gets refracted and bends away from the normal in the direction CX. Similarly, OD get refracted at D and bends away from the normal & goes in the direction DY. When the two refracted rays CX & CY are produced backwards, these appears to meet at point ‘I’ near the surface of water forming a virtual image of ‘O’. similarly, every point on the immersed part of OB of the stick appears to be lying along BI and thus, that is why stick appears bent in the direction of ‘BI’ instead of ‘BO’.
Home Work:
Q.1 Explain why a pool of water appears to e less deep than it actually is?
Q.2 Why a object (coin) placed under water appears to be raised?
Ans. Hint Due to refraction of light.
LENSES
Q.27 What is a lens? What are its types?
Ans. Lens:- A piece of transparent glass which is bounded by two spherical surfaces is known as a lens.
Spherical lenses are of two types:
1. Convex lens. 2. Concave lens.
1. Convex Lens:- A convex is thicker at the centre and thinner at the edges. It is also known as converging lens.
2. Concave Lens:- A concave lens is thinner at the centre and thicker at the edges. It is also known as diverging lens.
Q.28 Distinguish between convex lens and concave lens.
Ans.
|
Convex Lens |
Concave Lens |
|
1. It is thicker at the centre but thinner at the edges. 2. Its focal length if positive. 3. It converges light rays. 4. It may form real as well as virtual images. |
1. It is thinner at the centre and thicker at the edges. 2. Its focal length is negative. 3. It diverges light rays. 4. It always forms the real images. |
Q.29 Define the following terms:
i. Optical Centre ii. Principal Axis
iii. Principal Focus iv. Focal Length.
Ans.
i. Optical Centre:-The centre point of a lens is known as its optical centre. It is denoted by ‘O’
ii. Principal axis:- The line passing through the optical centre of a lens and perpendicular to both the faces of the lens is known as principal axis.
Iii. Principal focus:- The principal focus of a lens is a point on its principal axis to which the light rays parallel to the principal axis converges (in case of a convex lens ) or appears to diverge (in case of a concave lens).
iv. Focal length:- The distance between the optical centre and focus of the lens is called focal length.
Q.30 State the rules for obtaining images formed by convex lens.
Ans. An image is formed at that point where at least two refracted light rays meets or appears to meet.
Rule 1: A ray of light which is parallel to the principal axis of a convex lens passes through its focus after refraction through the lens.
Rule 2: A ray of light passing through the optical centre of the lens goes straight without any deviation through the lens.
Rule 3: A ray of light passing through the focus of a convex lens becomes parallel to its principal axis after refraction through the lens.
Q.31 Discuss the nature, position and size of the image formed by a convex lens.
Ans. The position, nature and size of the image formed by a convex lens depends upon the position of the object. The object can be placed at the following positions:
1. Between optical centre (c) and Principal Focus(F1):- When the object is placed between optical centre and principal focus(F1), the image formed is:
a. Behind the object on the same side of the lens as the object is
b. Virtual and erect
c. highly magnified.
2. At focus(F1):- When the object is placed at focus (F1), the image formed is:
a. at infinity
b. real and inverted
c. highly enlarged.
3. Between F1 and 2F1:- When the object is placed between F1 and 2F1, the image formed is:
a. beyond 2F2
b. real and inverted
c. larger than the object.
4. At 2F1:- When the object is placed at 2F1, the image formed is:
a. at 2F2
b. real and inverted
c. same size as that of the object.
5. Beyond 2F1:- When the object is placed beyond 2F1, the image formed is:
a. between F2 and 2F2.
b. real and inverted.
c. smaller than the object.
6. At infinity:- When the object is placed at infinity of the convex lens, the image formed is:
a. at focus (F2).
b. real and inverted.
c. highly diminished.
Q.32 State the rules for obtaining images formed by a concave lens.
Ans.
Rule 1: A ray of light which is parallel to the principal axis of a concave lens, appears to be coming from its focus after refraction through the lens.
Rule 2: A ray of light passing through the optical centre of a concave lens goes straight after passing through the lens.
Rule 3: A ray of light going towards the focus of a concave lens becomes parallel to the principal axis after refraction through the lens.
Q.33 What is the position, nature and size of the image formed by a concave lens?
Ans. In case of a concave lens, the object can be placed at the following two positions:
1. Anywhere between optical centre(O) and infinity:- When an object is placed anywhere between optical centre(o) and infinity of a convex lens, the iage formed is:
a. Between optical centre (O) and focus (F).
b. Virtual and erect.
c. Smaller than the object.
2. At infinity:- When the object is moved more and more away from the optical centre of the concave lens, the image becomes smaller and smaller in size and moves away from the lens towards focus. And when the object is at infinity, the image formed is:
a. At focus.
b. virtual and erect.
c. highly diminished.
Q.34 What is meant by power of lens?
Ans. Power of Lens:- We know that, when a ray of light passes through a lens after refraction, in general, it bends from its path. The extent of bending depends upon the focal length of the lens. It is found that smaller the focal length, greater is the capacity of the lens to bend the rays of light.
This property of a lens which determines the extent to which it can bend the rays of light passing through it, is called the power of lens. Power of lens is also defined as the reciprocal of the focal length of the lens (in meters).
i.e. Power of
lens=1Focal length
(in meters)
=> P=1f
The S.I. unit of power of lens is dioptre which is denoted by ‘D’
NOTE:- The power of a concave lens is negative and that of a convex lens is positive.
Dioptre:- One dioptre is the power of a lens whose focal length is one meter.
Problem 6:- A convex lens is of focal length 10 cm. what is its power?
Sol.
Here, focal length (f) = 10 cm = 10100m = 110m
Now, we know that
P=1/f
ðP = 1110
ðP = 10 D
Hence, power of lens is 10D.
Q.35 Write down the:
a. Lens formula
b. Magnification formulae for concave and convex lenses.
Ans.
a. Lens Formulae:- The lens formula for both concave and convex lenses is:
1v–1u=1f
Where, v = image distance
U = object distance
And f = focal length.
b. Magnification formulae:- The magnification formulae for spherical lenses (concave and convex) are as:
i. m=h2h1
Where, h2 = image height
And h1 = object height.
ii. m=vu
where, v = image distance
and u = object distance.
Q.36 What are the New Cartesian Sign Conventions for spherical lenses?
Ans. New Cartesian Sign Conventions:- New Cartesian sign conventions are used for measuring various distances in the ray-diagram of spherical lenses.
According to new Cartesian sign conventions:
i. All the distances are measured from the optical centre as origin.
ii. The distances measured in the same direction as that of incident light are taken as positive.
iii. The distances measured against the direction of incident light are taken as negative.
iv. Heights measured in upwards and perpendicular to the principal axis are taken as positive.
v. Heights measured in downwards and perpendicular to the principal axis are taken as negative.
Generally, the direction of incident ray of light is taken from left to right. In such a case, the distances measured from optical centre to the right is positive and to the left is negative.
Conclusions:-
1. An object is always placed to the left side of the lens. Thus, the object distance (u) is always negative.
2. The image formed by a convex lens can be either behind the lens or infront of it. So, the image distance (v) for a convex lens can either be positive or negative and vice versa.
3. In case of a concave lens, the image is always formed on the left side. So, the image distance (v) for a concave lens is always negative.
4. The focal length of a concave mirror is always negative while that of a concave mirror is always is always positive.
5. The object is always placed above the principal axis and in the upward direction. So, the object height (h1) is always positive.
6. If the image is formed above the principal axis, then it is taken as positive while if it is formed below the principal axis then, it is taken as negative.
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Prepared By: Sheikh Javaid Ahmad
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