 # 9th Science Guide Unit 6 Light Book Back Answers

## 9th Science Lesson 6 Light – English Medium

9th Science Book Back Answers Unit 6. 9th Science Lesson 6 Light Book Back Answers. 9th Standard Science Samacheer kalvi Guide Book Back Answers download PDF Tamil Medium and English Medium book in answers. 9th All Subject Guide. Class 9 Science Questions and Answers. Class 1 to 12 All Subject Guide. ## 9th Science Guide Unit 6 Light Book Back Answers

### I. Multiple choice questions:

#### 1. The field of view is maximum for ………………..

1. a) Plane mirror b) Concave mirror c) Convex mirror

(*FOV is the extent of the observable area that is seen at any given instant)

1. 0o
2. 45o
3. 90o

Ans : 45o

#### 3……………..is used as reflectors in torchlight.

1. Concave mirror
2. Convex mirror
3. Plane mirror

Ans : Concave mirror

#### 4. We can create enlarged, virtual images with

1. Concave mirror
2. Convex mirror
3. Plane mirror

Ans : Concave mirror

#### 5. When the reflection surface is curved outwards the mirror formed will be

1. Concave mirror
2. Convex mirror
3. Place mirror

Ans : Convex mirror

1. 5cm
2. 10cm
3. 5cm

Ans : 10cm

#### 7. When a beam of white light passes through a prism it gets

1. eflected
2. Deviated and dispersed
3. Only deviated

Ans : Deviated and dispersed

1. Vacuum
2. Glass
3. Diamond

Ans : Vacuum

#### 9. A real and enlarged image can be obtained by using a

1. Convex mirror
2. Plane mirror
3. Concave mirror

Ans : Concave mirror

#### 10. Which of the following statements about total internal reflection is true?

1. Angle of incidence should be greater than critical angle.
2. Light must travel from a medium of higher refractive index to a medium of lower refractive index.
3. Both (a) and (b)

Ans : 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. ( False )

Ans ; Due to the density of different medium the ray of light does not posses oblique.

1. IF the object is at infinity in form of a convex mirror the image is formed at infinity. ( False )

Ans: The image is at F.

1. An object is placed at a distance of 3cm from a plane mirror. The distance of the object and image is 3cm. ( False )

Ans : The distance of the object and image is 6cm.

1. The convex mirror always produces a virtual, diminished and erect image of the object. ( True )
2. The distance from centre of curvature of the mirror to the pole is called the focal length of the mirror. ( False )

Ans : The distance between pole and focus of a spherical mirror is called its focal length.

1. When an object is at the centre of curvature of concave mirror the image formed will be virtual and erect. ( False )

Ans : Real, inverted, equal in size at C.

1. Light is one of the slowest travelling energy with a speed of 3×108 ms-1 ( False )

Ans : Fastest travelling energy with a speed of 3×108 ms-1

1. The angle of incidence at which the angle of refraction is 0o is called the critical angle. ( False )

Ans : Angle of refraction is 90o

1. The reason for brilliance of diamonds is mainly due to total internal reflection of light. ( True )

### III. Fill in the blanks/complete the sentence

1. In going from a rarer to denser medium, the ray of light bends _____________

Ans : Towards normal

1. The ration of sine of the angle of incidence to the sine of _____________ is a constant.

Ans : Angle of refraction

1. The mirror used in search light is ______ Ans : Concave mirror
2. The angle of deviation of light ray in a prism depends on the angle of ________

Ans : incidence

1. The radius of curvature of a concave mirror whose focal length is 5cm is _________

Ans : 10cm

1. A spherical mirror whose reflecting surface is curved outwards is called _______ mirror.

Ans : Convex

1. Large _________ mirrors are used to concentrate sunlight to produce heat in solar furnaces.

Ans : Concave

1. All distances parallel to the principle axis are measured from the _____ of the mirror.

Ans : Pole

1. A negative sign in the value of magnification indicates that the image is ______

Ans : real

1. Light is refracted or bent while going from one medium to another because its _______, ________ changes. Ans : speed, wavelength

### IV. Match the following

 List I List II 1. Ratio of height of image to height of object. concave mirror 2. Used in hairpin bends in mountains total internal reflection 3. Coin inside water appearing slightly raised magnification 4. Mirage convex mirror 5. Used as Dentist’s mirror refraction Ans : 1 – C, 2 – D, 3 – E, 4 – B, 5 – A

1. ii) Position of object Position of image Size and nature of image
 1. Within focus Between F and C Magnified , Real, inverted 2. At focus F At C Magnified, virtual, erect 3. Between F and C Behind the mirror Diminished, Real, inverted 4. At C Infinity Highly Diminished, Real, inverted 5. Beyond C At F Highly Magnified , Real, inverted 6. At infinity Beyond C 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:

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

1. If both assertion and reason are true and reason is the correct explanation.
2. If assertion is true but reason is false.
3. If Assertion is false but reason is true.

Ans : If Assertion is false but reason is true.

1. 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

1. If both assertion and reason are true and reason is the correct explanation.
2. If assertion is true but reason is false.
3. If Assertion is false but reason is true.

Ans : If both assertion and reason are true and reason is the correct explanation.

### VI. Very short answer type:

1. Water
2. Glass

#### 2. According to Cartesion sign convention which mirror and which lens has negative focal length?

1. Concave mirror
2. Concave lens

#### 3. A coin in a glass beaker appears in rise as the beaker is slowly filled with water, why?

Due to the refraction

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

1. Concave mirror
2. Concave mirror

#### 5. Name the spherical mirror(s) that has/have (i) virtual principle focus (ii) Real principle focus

1. Convex mirror
2. Concave mirror

#### 6. If an object is placed at the focus of a concave mirror, where is the image formed?

The image is formed at infinity.

Speed of light

#### 8. What is speed of light in vacuum? Who first measured the speed of light?

• Speed of light in vacuum is 3 x 108 ms-1
• In 1665 the Danish astronomer Ole Roemer first estimated the speed of light.

#### 9. Concave mirrors are used by dentists to examine teeth. Why?

It gives a magnified image of teeth.

#### 10. Pick Out the concave and convex mirrors from the following and tabulate them.

(Rear-View, mirror, Dentists mirror, Torch-light mirror, Mirrors in shopping malls, Make-up mirror

Concave mirror Convex mirror