# CBSE Solutions for Class 10 English

#### GSEB std 10 science solution for Gujarati check Subject Chapters Wise::

Power of convex lens is positive and concave lens is ………………

જવાબ : negative

……………. is ratio of height of image to height of object

જવાબ : Magnification

The dentists use ………….. mirror to see large images of teeth of patients.

જવાબ : concave

When rays of light after reflection meet a point ………….. image is formed.

જવાબ : real

According to laws of reflection, the angle of incidence is equal to angle of ……………..

જવાબ : reflection

When light falls on a surface and bounces back to the medium, the phenomena is called ……………..

જવાબ : reflection

No matter how far you stand from a spherical mirror, your image appears erect. The mirror may be ………. .

જવાબ : plane or convex mirror

A ………. mirror is used as a head mirror by the doctors to concentrate light on the body parts to be examined

જવાબ : concave

A positive sign in the value of magnification indicates that the image is ……….

જવાબ : virtual

A ………. lens will always give a virtual, erect and diminished image, irrespective of the position of the object.

જવાબ : concave

The SI unit of power is ………. .

જવાબ : dioptre

Power of’ a lens is the ………. of its focal length.

જવાબ : reciprocal

The speed of light in vacuum is ………. .

જવાબ : 3 x 108 m/s

Light shows the phenomena of reflection, refraction and ………. .

જવાબ : dispersion

A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

જવાબ : Power of lens (P) = 1/f P = 1.5D f = 1/1.5 = 10/15 = 0.66 m A convex lens has a positive focal length. Therefore, it is a convex lens or a converging lens.

Find the focal length of a lens of power -2.0 D. What type of lens is this?

જવાબ : Power of lens (P) = 1/f P = -2D f = -1/2 = -0.5 m A concave lens has a negative focal length. Therefore, it is a concave lens

The magnification produced by a plane mirror is +1. What does this mean?

જવાબ : The positive sign means an image formed by a plane mirror is virtual and erect. Since the magnification is 1 it means that the size of the image is equal to the size of the object.

One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

જવાબ : Yes, it will produce a complete image of the object, as shown in the figure. This can be verified experimentally by observing the image of a distant object like a tree on a screen when the lower half of the lens is covered with a black paper. However, the intensity or brightness of the image will reduce.

Name the type of mirror used in the following situations.

(b) Side/rear-view mirror of a vehicle

(c) Solar furnace

જવાબ : (a) Concave Mirror: Because concave mirrors can produce a powerful parallel beam of light when the light source is placed at their principal focus. (b) Convex Mirror: Because of its largest field of view. (c) Concave Mirror: Because it concentrates the parallel rays of the sun at a principal focus.

We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

જવાબ : Range of the distance of the object = 0 to 15 cm from the pole of the mirror. Nature of the image = virtual, erect, and larger than the object.

Find the power of a concave lens of focal length 2 m.

જવાબ : Focal length of concave lens (f) = 2 m Power of lens (P) = 1/f = 1/ (-2) = -0.5D

Define 1 dioptre of power of a lens.

જવાબ : Dioptre is the SI unit of power of lens is denoted by the letter D. 1 dioptre can be defined as the power of a lens of focal length 1 metre.

The refractive index of diamond is 2.42. What is the meaning of this statement?

જવાબ : Diamond has a refractive index of 2.42 which means that the speed of light in diamond will reduce by a factor of 2.42 as compared to its speed in the air. In other words, the speed of light in diamond is 1/2.42 times the speed of light in vacuum.

Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 x 108 ms-1.

જવાબ : Refractive index of a medium (nm) = Speed of light in vacuum/Speed of light in the medium Speed of light in vacuum (c) = 3 × 108 m/s Refractive index of glass (ng) = 1.50 Speed of light in the glass (v) = Speed of light in vacuum/ Refractive index of glass = c/ng =3 × 108/1.50 = 2x 108 ms-1.

A ray of light travelling in air enters obliquely into water. Does the light ray bends towards the normal or away from the normal? Why?

જવાબ : The light ray bends towards the normal. When a light ray enters from an optically rarer medium (which has low refractive index) to an optically denser medium (which has a high refractive index), its speed slows down and bends towards the normal. As water is optically denser than air, a ray of light entering from air into water will bend towards the normal.

The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

જવાબ : Radius of curvature (R) = 20 cm Radius of curvature of the spherical mirror = 2 × Focal length (f) R = 2f f= R/2 = 20 / 2 = 10 Therefore, the focal length of the spherical mirror is 10 cm.

Why do we prefer a convex mirror as a rear-view mirror in vehicles?

જવાબ : Convex mirror is preferred as a rear-view mirror in cars and vehicles as it gives a wider field of view, which helps the driver to see most of the traffic behind him. Convex mirrors always form an erect, virtual, and diminished image of the objects placed in front of it.

Find the focal length of a convex mirror whose radius of curvature is 32 cm.

જવાબ : Radius of curvature (R) = 32 cm Radius of curvature = 2 × Focal length (f) R= 2f f = R/2 = 32/2 = 16 Therefore, the focal length of the given convex mirror is 16 cm.

A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located?

જવાબ : Magnification produced by a spherical mirror:

Define the principal focus of a concave mirror.

જવાબ : Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is called the principal focus of the concave mirror.

Define focal length of a spherical mirror.

જવાબ : The distance between the pole and principal focus of a spherical mirror is called focal length of the spherical mirror.

Define the principal focus of a concave mirror.

જવાબ : A point on the principal axis, where the rays of light parallel to the principal axis meet after reflection from the concave mirror is called the principal focus of the concave mirror.

Define the principal focus of a convex mirror.

જવાબ : A point on the principal axis, where rays of light parallel to the principal axis appear to meet after reflecting from the convex mirror.

Define reflection of light ?

જવાબ : The process of returning or bouncing back the light to the same medium after striking the surface is called reflection of light.

What is a reflector ?

જવાબ : A surface which reflects the light is called reflector.

State laws of reflection.

જવાબ :

1. Angle of incidence is equal to the angle of reflection. That is , ∠i = ∠r .
2. Incident ray, reflected ray and normal to the reflecting surface at the point of incidence lie in the same plane.

What are the values of angle of incidence ∠i and angle of reflection ∠r for normal incidence of light on a plane mirror ? [CBSE (All India) 2005]

જવાબ : For normal incidence, ∠i = 0. Therefore, according to law of reflection ∠r = ∠i = 0.

What is real image ?

જવાબ : When rays of light from an object actually meet at a point after refraction, then image formed is real.

Mention the nature of image produced by a plane mirror. (CBSE 2014)

જવાબ : Image is virtual, erect and of the same size as that of the object.

What is virtual image ?

જવાબ : When rays of light from an object do not meet at a point but appears to meet at a point, then image formed is virtual.

Define centre of curvature of a spherical mirror.

જવાબ : The centre of a hollow sphere of which the spherical mirror forms a part is called the centre of curvature of the spherical mirror.

Define radius of curvature of a spherical mirror.

જવાબ : The radius of a hollow sphere of which the spherical mirror forms a part is called radius of curvature of the spherical mirror.

Define aperture of a spherical mirror.

જવાબ : The part of spherical mirror exposed to the incident light is called the aperture of the spherical mirror.

Define pole of a spherical mirror.

જવાબ : The mid point of the spherical mirror is called the pole of spherical mirror.

Define principal axis of the spherical mirror.

જવાબ : The line joining the centre of curvature and pole of the spherical mirror and extended on either side is called the principal axis of the spherical mirror.

Name the mirror that can give an erect and enlarged image of an object.

જવાબ : The mirror that can give an erect and enlarged image of an object is Concave Mirror. Object distance (u) = – 10 cm

v = 3 × (- 10) = – 30 cm

Therefore, the negative sign indicates that an inverted image is formed in front of the given concave mirror at a distance of 30 cm.

A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.

જવાબ : The position of the image should be at 2F since the image is the real and same size.

It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Therefore, the needle is placed in front of the lens at a distance of 50 cm.

Object distance (u) = – 50 cm

Image distance, (v) = 50 cm

Focal length = f

According to the lens formula, An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.

જવાબ : Height of the Object, h0 = 5 cm

Distance of the object from converging lens, u = -25 cm

Focal length of a converging lens, f = 10 cm

Using lens formula, Thus, the image is inverted and formed at a distance of 16.7 cm behind the lens and measures 3.3 cm. The ray diagram is shown below. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.

જવાબ : Focal length of convex mirror (f) = +15 cm

Object distance (u) = – 10 cm

According to the mirror formula, The image is located at a distance of 6 cm from the mirror on the other side of the mirror.

The positive and a value of less than 1 of magnification indicates that the image formed is virtual and erect and diminished.

The magnification produced by a plane mirror is +1. What does this mean?

જવાબ : Magnification produced by a mirror is given by the relation The magnification produced by a plane mirror is +1. It shows that the image formed by the plane mirror is of the same size as that of the object. The positive sign shows that the image formed is virtual and erect.

We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

જવાબ : Range of object distance = 0 cm to15 cm

A concave mirror gives an erect image when an object is placed between its pole (P) and the principal focus (F).

Hence, to obtain an erect image of an object from a concave mirror of focal length 15 cm, the object must be placed anywhere between the pole and the focus. The image formed will be virtual, erect, and magnified in nature, as shown in the given figure. Find the power of a concave lens of focal length 2 m.

જવાબ : Focal length of concave lens, = 2 m Here, negative sign arises due to the divergent nature of concave

A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.

જવાબ : When an object is placed at the centre of curvature, 2F1, of a convex lens, its image is formed at the centre of curvature, 2F2, on the other side of the lens. The image formed is inverted and of the same size as the object, as shown in the given figure. It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Hence, the needle is placed in front of the lens at a distance of

50 cm.

Object distance, u = −50 cm

Image distance, v = 50 cm

Focal length = f

According to the lens formula, Hence, the power of the given lens is +4 D.

Define 1 dioptre of power of a lens.

જવાબ : Power of lens is defined as the reciprocal of its focal length. If P is the power of a lens of focal length F in metres, then The S.I. unit of power of a lens is Dioptre. It is denoted by D.

1 dioptre is defined as the power of a lens of focal length 1 metre.

1 D = 1 m−1

The refractive index of diamond is 2.42. What is the meaning of this statement?

જવાબ : Refractive index of a medium nm is related to the speed of light in that medium v by the relation: Where, c is the speed of light in vacuum/air

The refractive index of diamond is 2.42. This suggests that the speed of light in diamond will reduce by a factor 2.42 compared to its speed in air.

Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 108 m s−1.

જવાબ : Refractive index of a medium nm is given by, A concave mirror produces three times magnified (enlarged) real image of object placed at 10 cm in front of it. Where is the image located?

જવાબ : Magnification produced by a spherical mirror is given by the relation, Object distance, u = −10 cm

v = 3 × (−10) = −30 cm

Here, the negative sign indicates that an inverted image is formed at a distance of
30 cm in front of the given concave mirror.

Find the focal length of a convex mirror whose radius of curvature is 32 cm.

જવાબ : Radius of curvature, R = 32 cm

Radius of curvature = 2 × Focal length (f)

R = 2f Hence, the focal length of the given convex mirror is 16 cm.

The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

જવાબ : Radius of curvature, R = 20 cm

Radius of curvature of a spherical mirror = 2 × Focal length (f)

R = 2f Hence, the focal length of the given spherical mirror is 10 cm.

A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located?

જવાબ : Magnification produced by a spherical mirror: Object distance (u) = – 10 cm

v = 3 × (- 10) = – 30 cm

Therefore, the negative sign indicates that an inverted image is formed in front of the given concave mirror at a distance of 30 cm.

An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image. 

જવાબ : Given: u = -10 cm, f = 15 cm and v = ? Hence, the image is formed behind the mirror. It is erect, virtual and smaller than the object.

Find out, from Table, the medium having highest optical density. Also find the medium with lowest optical density.

 Material medium Refractive index Material medium Refractive index Air 1.0003 Canada Balsam 1.53 Ice 1.31 – – Water 1.33 Rock salt 1.54 Alcohol 1.36 – – Kerosene 1.44 Carbon disulphide 1.63 Fused quartz 1.46 Dense flint glass 1.65 Turpentine oil 1.47 Ruby 1.71 Benzene 1.50 Sapphire 1.77 Crown glass 1.52 Diamond 2.42

જવાબ : Lowest optical density = Air

Highest optical density = Diamond

The optical density of a medium is directly related to its refractive index. A medium with the highest refractive index will have the highest optical density and vice-versa.

It can be observed from the table that air and diamond respectively have the lowest and highest refractive index. Hence, air has the lowest optical density and diamond has the highest optical density.

An object 5 cm is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position, nature and size of the image.

જવાબ : Object distance (u) = – 20 cm

Object height (h) = 5 cm

Radius of curvature (R) = 30 cm

Radius of curvature = 2 × Focal length

R = 2f

f = 15 cm

According to the mirror formula, The positive value of image height indicates that the image formed is erect.

Hence, the image formed is erect, virtual, and smaller in size.

An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed so that a sharply focused image can be obtained? Find the size and nature of the image.

જવાબ : Object distance (u) = – 27 cm

Object height (h) = 7 cm

Focal length (f) = – 18 cm

According to the mirror formula, The negative value of image height indicates that the image formed is inverted.

An object is placed at the following distances from a concave mirror of focal length 15 cm.
(a) 10 cm
(b) 20 cm
(c) 30 cm
(d) 40 cm
Which position of the object will produce

1. Virtual image
2. A diminished real image
3. An enlarged real image
4. An image of same size. (CBSE 2011, 2012)

જવાબ :

1. Concave mirror forms virtual image if object is placed between the focus and pole of the mirror. Therefore, for the position of object at 10 cm mirror forms the required image.
2. A real and diminished image is formed when object lies beyond C i.e. beyond 2F. So, for the position of object at 40 cm, mirror forms the required image.
3. An enlarged real image is formed when object lies between F and 2 F. So, for the position of object at 20 cm, mirror forms the required image.
4. An image of same size of the object is formed when object lies at C or 2F. So, for the position of object at 30 cm, mirror forms the required image.

State three uses of a concave mirror. (CBSE 2012)

જવાબ :

1. Reflector: Concave mirrors are used in motor head lights, search lights and torches etc. to produce an intense parallel beam of light. A bulb is placed at the focus of concave mirror or concave reflecting surface. The beam of light from the bulb after reflecting from the concave mirror goes as a parallel beam (figure 24). This parallel beam of – light illuminates the road ahead of the vehicle.
2. Shaving and make up mirror: When an object is placed close to a concave mirror (i.e between the pole and focus of the concave mirror), an erect and enlarged (large in
size) image of the object is formed. Because of this fact, concave mirror is used by men to see their enlarged faces while shaving. Similarly, a lady can see her face better with the help of a concave mirror while doing make up.
3. In solar cookers: When a parallel beam of sun light falls on a concave mirror, this beam is brought to the focus of the concave mirror. As a result of this, the temperature of an object (say a container containing un-cooked food) placed at this focus increases considerably. Hence the food in the container is cooked (figure 25). State two uses of a convex mirror. (CBSE 2012)

જવાબ :

1. Rear view or driver’s mirror. Convex mirror is used as a rear view mirror in vehicles because this mirror forms an erect and diminished image of an object behind the vehicle. Since the image of the object formed is small in size, so the field of view is increased. It means, the driver of a vehicle can see the traffic over large area behind his vehicle. This mirror is also known as driver’s mirror.
2. In street lights. Convex mirror is used in street lights to diverge light over a large area (figure 28). How can you identify the three types of mirrors without touching ? (CBSE 2011)

જવાબ : We can identify the three types of mirrors by looking at them. If the size of the image of an object is of the
same size as that of the object, then mirror is plane mirror. If the size of the image of an object increases as the object is brought closer to the mirror and the size of image is highly magnified when the object is very close to the mirror, then the mirror is concave mirror. If the size of the image is smaller and full length of the image of an object is seen, then the mirror is convex mirror.

A concave mirror of focal length ft can form a magnified erect as well as an inverted image of an object
placed in front of it. ” Justify this statement stating the position of the object with respect to the mirror in each case for obtaining these images. (CBSE 2013)

જવાબ :

1. When object is placed between the focus (F) and pole (P) of a concave mirror, magnified and erect image of the object is formed on the back of the mirror.
2. When object is placed between the centre of curvature and the principal focus of a concave mirror, magnified and inverted image is formed in front of the mirror.

State laws of refraction of light. [CBSE (Foreign) 2004, 2012, 2013, 2014, 2015]

જવાબ : Refraction of light follows the following two laws :

1. The incident ray, the refracted ray and the normal to the surface separating the two media all lie in the same plane  This law is also known as Snell’s law as it was stated by Prof. Willebrord Snell (Dutch mathematician and astronomer).

What is the difference between a convex lens (converging lens) and a concave lens (diverging lens) ?
(CBSE 2012)

જવાબ :

 Convex lens Concave lens 1.  It is thick in the middle and thin at edges. 1.  It is thin in middle and thick at edges. 2.  When placed close to eye, it forms magnified image of an object. For example, if you place it close to your book, the words will appear large in size. 2.    It forms diminished image of an object. If you place it close to your book, the words will appear small in size.

A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object. Also, find the power of the lens.

જવાબ : Given: v = 50 cm, u = ?, P = ?
Since the image is equal to the size of the object, so the object is placed at a distance twice the focal length of the lens, i.e.
-u = v = 2f= 50 cm
u = -50 cm and f= 25 cm
Hence, the needle is placed at a distance of 50 cm in front of the lens.
Nowpower, One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observation. 

જવાબ : Yes, it will produce a complete image of the object. This can be verified experimentally as follows:
Procedure:

1. Take a metre scale and place it horizontally against a white or light coloured wall with 0 cm end touching the wall.
2. Take a convex lens and focus the light from a distant object, say a tree, by moving the lens to and fro along the metre scale.
3. A sharp image of the tree is formed on the wall at a distance equal to the focal length of the lens.
4. Cover lower or upper half of the lens with black paper.
5. Again focus the light from the same tree on the wall.A less bright image of the tree is formed on the wall from the same point on the metre scale. Observation: It is observed that when half of the lens is covered, its focal length remains the same. Only the intensity of light entering the lens decreases due to which the brightness of the image also decreases.
Diagrammatically, it can be represented as An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed. 

જવાબ : The ray diagram is shown below: ### There are No Content Availble For this Chapter

 Concave lens is also known as Focus Mirror used as rear view mirror Concave Mirror used by dentist Real image A point on principal axis of lens where all rays of light parallel to the principal axis meets or appear to meet. Diverging lens The image which can be obtained on screen Convex

જવાબ :

a. Diverging lens
b. Convex
c. Concave
d. Focus
e. Real image

 The deviation of light ray from its path when it travels from one medium to another Converging lens Magnification of plane mirror Refraction Convex lens is also known as One

જવાબ :

a. Refraction
b. One
c. Converging lens

 Column I Column II (a) Mirror having magnification always equal to one (m = 1) (i) concave mirror (b) Mirror used to concentrate sunlight in reflecting solar cooker (ii) refraction (c) Image can be obtained on screen (iii) plane mirror (d) Bottom of a tank containing water appears to be raised due to (iv) convex lens (e) The lens having power – 2D (v) real image (f) The lens which is thicker at middle as compared to edges (vi) concave lens (g) Mirror used as rear-view mirror in vehicles (vii) convex mirror

જવાબ :

 Column I Column II (a) Mirror having magnification always equal to one (m = 1) (iii) plane mirror (b) Mirror used to concentrate sunlight in reflecting solar cooker (i) concave mirror (c) Image can be obtained on screen (v) real image (d) Bottom of a tank containing water appears to be raised due to (ii) refraction (e) The lens having power – 2D (vi) concave lens (f) The lens which is thicker at middle as compared to edges (iv) convex lens (g) Mirror used as rear-view mirror in vehicles (vii) convex mirror