## Samacheer Kalvi 9th Term I Science Book Back Question and Answers – Unit 3:

Samacheer Kalvi 9th Standard New Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 9 New Syllabus 2021 to 2022 Book Back Ques & Ans solutions available for both English and Tamil Medium. Class 9 Science Book Term 1 Unit 3 – Light Answers/Solutions are provided on this page. 9th Std Science Book is of Term 1st, 2nd, 3rd, and consists of 9 Units in each Term. All 9 Units of Term 1st, 2nd, 3rd Science Book Back One, and Two Mark Solutions are given below.

Check Unit wise and  9th New Science Book Back Question and Answers Guide/Solutions PDF format for Free Download.English, Tamil, Maths, Science, and Social Science Book Back Questions and Answers available in PDF. Check Science – Physics, Chemistry, and Biology, Social Science – History, Geography, Civics, Economics below. See below for the Samacheer Kalvi 9th Science Book Back Unit 3 Term 1 PDF:

### Samacheer Kalvi 9th Science Book Back Unit 3 Term 1 Solutions Guide PDF:

Science Subject 1 Mark and 2 Mark Solutions Guide PDF available below. Click the Download option to download the book back 1 Mark & 2 Mark questions and answers. Take the printout and use it for exam purposes.

### Unit – 3

Light

I. Multiple choice questions:

1. The field of view is maximum for ………………..
a) Plane mirror b) Concave mirror c) Convex mirror
(*FOV is the extent of the observable area that is seen at any given instant)

2. When a ray of light passes from one medium to another medium, refraction takes place when angle of incidence is.
a) 0° b) 45° c) 90°

3… is used as reflectors in torchlight.
a) Concave mirror b) Convex mirror c) Plane mirror

4. We can create enlarged, virtual images with
a) Concave mirror b) Convex mirror c) Plane mirror

5. When the reflection surface is curved outwards the mirror formed will be
a) Concave mirror b) Convex mirror c) Place mirror

6. The focal length of a concave mirror is 5cm. its rwinmaeen.com dius of curvature is
a) 5cm b) 10cm c) 2.5cm

7. When a beam of white light passes through a prism it gets
a) reflected b) Deviated and dispersed c) Only deviated

8. The speed of light is maximum in
a) Vacuum b) Glass c) Diamond

9. A real and enlarged image can be obtained by using a
a) Convex mirror b) Plane mirror c) Concave mirror

10. Which of the following statements about total internal reflection is true?
a) Angle of incidence should be greater than critical angle.
b) Light must travel from a medium of higher refractive index to a medium of lower refractive index.
c) Both (a) and (b)

II. True or false – if false give the correct answer

1. The angle of deviation depends on the refractive index of the glass. – True

2. If a ray of light passes obliquely from one medium to another, it does not suffer any deviation.
Ans: False. Due to the density of different medium the ray of light does not posses oblique.

3. IF the object is at infinity in form of a convex mirror the image is formed at infinity.
Ans: False. The image is at F.

4. An object is placed at a distance of 3cm from a plane mirror. The distance of the object and image is 3cm.
Ans: False. The distance of the object and image is 6cm.

5. The convex mirror always produces a virtual, diminished and erect image of the object.
Ans: True

6. The distance from centre of curvature of the mirror to the pole is called the focal length of the mirror.
Ans: False. The distance between pole and focus of a spherical mirror is called its focal length.

7. When an object is at the centre of curvature of concave mirror the image formed will be virtual and erect.
Ans: False. Real, inverted, equal in size at C.

8. Light is one of the slowest travelling energy with a speed of 3x108ms-1                                                                                Ans: False. Fastest travelling energy with a speed of 3x108ms-1

9. The angle of incidence at which the angle of refraction is 0o is called the critical angle.
Ans: False. Angle of refraction is 90 o

10. The reason for brilliance of diamonds is mainly due to total internal reflection of light.
Ans: True

III. Fill in the blanks/complete the sentence

1. In going from a rarer to denser medium, the ray of light bends Towards normal
2. The ration of sine of the angle of incidence to the sine of Angle of refraction is a constant.
3. The mirror used in search light is Concave mirror
4. The angle of deviation of light ray in a prism depends on the angle of incidence
5. The radius of curvature of a concave mirror whose focal length is 5cm is 10cm
6. A spherical mirror whose reflecting surface is curved outwards is called Convex mirror.
7. Large Concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.
8. All distances parallel to the principle axis are measured from the Pole of the mirror.
9. A negative sign in the value of magnification indicates that the image is real
10. Light is refracted or bent while going from one medium to another because its speed, wavelength
changes.

IV. Match the following:

I. List I                                                                                     List II
1. Ration of height of image to height of object    – a) Concave mirror
2. Used in hairpin bends in mountains.                 – b) Total internal reflection.
3. Coin inside water appearing slightly raised.     – c) Magnification
4. Mirage                                                                       – d) Convex mirror
5. Used as dentists mirror                                         – e) refraction
Ans: 1 – c; 2 – d ; 3 – e ; 4 – b; 5- a

 2. Position of object –           position of image –           size and nature of image 1. Within focus –           a) Between F and C –           A) Magnified, Red, inverted 2. At focus F –           b) At C –           B) Magnified, Virtual, erect 3. Between F and C –           c) Behind the mirror –           C) Diminished, Red, inverted 4. At C –           d) Infinity –           D) Highly Diminished, Real,                                inverted. 5. Beyond C –           e) At F –           E) Highly magnified, Real, inverted. 6. At infinity –           f) Beyond C –           F) Same size, real, inverted

Ans: 1–c-B; 2-d-E; 3-f-A; 4-b-F; 5-a-C; 6-e-D

V. Assertion & Reason:

In the following questions, the statement of assertion is followed by a reason. Mark the correct choice as:
a) If both assertion and reason are true and reason is the correct explanation.
b) If assertion is true but reason is false.
c) If Assertion is false but reason is true.

1. Assertion : For observing the traffic at a hairpin bend in mountain paths a plane mirror is preferred over convex mirror and concave mirror.
Reason : A convex mirror has a much larger field of view than a plane mirror or a concave mirror.
Ans: c) If Assertion is false but reason is true.

2. Assertion : Incident ray is directed towards the centre of curvature of spherical mirror. After reflection it retraces its path.
Reason : Angle of incidence I = Angle of reflection r = 0o
Ans: a) If both assertion and reason are true and reason is the correct explanation.

1. Give two examples of transparent medium that are denser than air.
Ans: i) Water ii) Glass

2. According to Cartesion sign convention which mirror and which lens has negative focal length?
Ans: i) Concave mirror ii) Concave lens

3. A coin in a glass beaker appears in rise as the beaker is slowly filled with water, why?
Ans: Due to the refraction

4. Name the mirror(s) that can give (i) an erect and enlarged image, (ii) same sized, inverted image.
Ans: (i) Concave mirror (ii) Concave mirror

5. Name the spherical mirror(s) that has/have (i)winm even.com irtual principle focus (ii) Real principle focus
Ans: (i) Convex mirror (ii) Concave mirror

6. If an object is placed at the focus of a concave mirror, where is the image formed?                                                            Ans: The image is formed at infinity.

7. Why does a ray of light bend when it travels from one medium to another?
Ans: Speed of light

8. What is speed of light in vacuum? Who first measured the speed of light?
Ans: i) Speed of light in vacuum is 3 x 108ms-1
ii) In 1665 the Danish astronomer Ole Roemer first estimated the speed of light.

9. Concave mirrors are used by dentists to examine teeth. Why?
Ans: It gives a magnified image of teeth.