In this post we are going to share the detailed solution for class 10th science chapter 10 . All the solutions are prepared by our esteemed teachers who are very well experienced in the teaching.
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Complete Science Solutions Chapter Wise : Class 10th NCERT Science Solutions – All Chapters
Chapter 10 Solutions
EXERCISE – 1
QUE:-1 Define the principal focus of a concave mirror
ANS:-
The principal focus of a concave mirror is a point on its principal axis to which all the light rays which are parallel and close to the axis, converge after reflection from the concave mirror.
QUE:-2 The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
ANS:-
Focal length = 12 x Radius of curvature = 12 x 20 cm = 10 cm
QUE:-3 Name a mirror that can give an erect and enlarged image of an object.
ANS:-
Concave mirror.
QUE:-4 Why do we prefer a convex mirror as a rear-view mirror in vehicles?
ANS:-
We prefer a convex mirror as a rear-view mirror in vehicles because of two reasons :
- A convex mirror always produces an erect image of the objects.
- The image formed in a convex mirror is highly diminished or much smaller than the object, due to which a convex mirror gives a wide field of view of the traffic behind. A convex mirror enables the driver to view such larger area of the traffic behind him.
EXERCISE – 2
QUE:-1 Find the focal length of a convex mirror whose radius of curvature is 32 cm
ANS:-
R = +32 cm and f=R/2=+32/2=+16cm
QUE:-2 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?
ANS:-
Because the image is real, so magnification m must be negative.
Thus the image is located at a distance of 30 cm from the mirror on the object side of the mirror.
EXERCISE – 3
QUE:-1 A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
ANS:-
The light-ray bends towards the normal because the ray of light goes from a rarer medium to a denser medium.
QUE:-2 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.
ANS:-
Refractive index of glass, n8 = 1.50
QUE:-3 Find out, from Table 10.3, the medium having highest optical density. Also find the medium with lowest optical density.
ANS:-
From table 10.3, diamond has highest refractive index (= 2.42), so it has highest optical density.
Air has lowest refractive index (= 1.0003), so it has lowest optical density.
QUE:-4 You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table 10.3.
ANS:-
For kerosene, n = 1.44
For turpentine, n = 1.47
For water, n = 1.33
Because water has the lowest refractive index, therefore light travels fastest in this optically rarer medium than kerosene and turpentine oil.
QUE:-5 The refractive index of diamond is 2.42. What is the meaning of this statement?
ANS:-
By saying that the refractive index of diamond is 2.42, we mean that the speed of light in diamond is lower by a factor of 2.42 relative to that in vacuum.
EXERCISE – 4
QUE:-1 Define 1 dioptre of power of a lens .
ANS:-
One dioptre is the power of a lens whose focal length is 1 metre.
QUE:-2 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.
ANS:-
Here ν = +50cm
Because the real image is of the same size as the object,
QUE:-3 Find the power of a concave lens of focal length 2 m.
ANS:-
Because the focal length of a concave lens is negative,
therefore f = -2 m
EXERCISE – 5 (CHAPTER END QUESTION)
QUE:-1 Which one of the following materials cannot be used to make a lens?
(a) Water (b) Glass (c) Plastic (d) Clay
ANS:-
(d) Clay
QUE:-2 The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
(a) Between the principal focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus.
ANS:-
(d) Between the pole of the mirror and its principal focus.
QUE:-3 Where should an object be placed in front of a convex lens to get a real image of the size of the object?
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus.
ANS:-
(b) At twice the focal length.
QUE:-4 A spherical mirror and a thin spherical lens have each a focal length of –15 cm. The mirror and the lens are likely to be
(a) both concave.
(b) both convex.
(c) the mirror is concave and the lens is convex.
(d) the mirror is convex, but the lens is concave.
ANS:-
(a) Both concave
QUE:-5 No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
(a) plane.
(b) concave.
(c) convex.
(d) either plane or convex.
ANS:-
(d) Either plane or convex.
QUE:-6 Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
(a) A convex lens of focal length 50 cm.
(b) A concave lens of focal length 50 cm.
(c) A convex lens of focal length 5 cm.
(d) A concave lens of focal length 5 cm.
ANS:-
(c) A convex lens of focal length 5 cm.
QUE:-7 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.
ANS:-
A concave mirror gives an erect image when the object is placed between the focus F and the pole P of the concave mirror, i.e., between 0 and 15 cm from the mirror. The image thus formed will be virtual, erect and larger than the object.
QUE:-8 Name the type of mirror used in the following situations.
(a) Headlights of a car.
(b) Side/rear-view mirror of a vehicle.
(c) Solar furnace. Support your answer with reason.
ANS:-
(a) Concave mirrors are used as reflectors in headlights of cars. When a bulb is located at the focus of the concave mirror, the light rays after reflection from the mirror travel over a large distance as a parallel beam of high intensity.
(b) A convex mirror is used as a side/rear-view mirror of a vehicle because
- A convex mirror always forms an erect, virtual and diminished image of an object placed anywhere in front it.
- A convex mirror has a wider field of view than a plane mirror of the same size.
(c) Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces
QUE:-9 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.
ANS:-
Yes, even when one half of the lens is covered with a black paper, complete image of the object will be formed. Take a convex lens and focus the light from a distant object onto a screen. As expected an image (sharp) is formed at a distance equal to the focal length Cover the lower or the upper half of the lens and focus the light from the same object onto the same screen. You will be able to get a sharp image again; however the brightness of the image will be less in the second case. The same effect w,ll be seen even if the lens is half covered with black strips.
QUE:-10 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.
ANS:-
Therefore, the mage ¡s formed between F2 and 2F2 on the other side of the lens. It is real and inverted, and smaller in size than the object.
QUE:-11 A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
ANS:-
QUE:-12 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.
ANS:-
f = +15 cm. u = -1o cm
For mirror, we have
The image must be virtual and erect.
QUE:-13 The magnification produced by a plane mirror is +1. What does this mean?
ANS:-
This means that size of the image is equal to the size of the object.
QUE:-14 An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size.
ANS:-
QUE:-15 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 sharp focussed image can be obtained? Find the size and the nature of the image.
ANS:-
QUE:-16 Find the focal length of a lens of power – 2.0 D. What type of lens is this?
ANS:-
QUE:-17 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?
ANS:-
SUMMARY OF THE CHAPTER
* Light seems to travel in straight lines.
* Mirrors and lenses form images of objects. Images can be either real or virtual, depending on the position of the object.
* The reflecting surfaces, of all types, obey the laws of reflection. The refracting surfaces obey the laws of refraction.
* New Cartesian Sign Conventions are followed for spherical mirrors and lenses
* Mirror formula,1/V+1/U=1/F, gives the relationship between the object-distance (u),image-distance (v), and focal length (f) of a spherical mirror.
* The focal length of a spherical mirror is equal to half its radius of curvature.
*The magnification produced by a spherical mirror is the ratio of the height of the image to the height of the object.
* A light ray travelling obliquely from a denser medium to a rarer medium bends away from the normal. A light ray bends towards the normal when it travels obliquely from a rarer to a denser medium.
* Light travels in vacuum with an enormous speed of 3×108 m s-1. The speed of light is different in different media.
* The refractive index of a transparent medium is the ratio of the speed of light in vacuum to that in the medium.
* In case of a rectangular glass slab, the refraction takes place at both air-glass interface and glass-air interface. The emergent ray is parallel to the direction of incident ray.
* Lens formula,1/V-1/U=1/F , gives the relationship between the object-distance (u),image-distance (v), and the focal length (f) of a spherical lens.
* Power of a lens is the reciprocal of its focal length. The SI unit of power of a lens is dioptre.
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Complete Science Solutions Chapter Wise : Class 10th NCERT Science Solutions – All Chapters
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