Samacheer Kalvi 9th Science Solutions Chapter 6 Pdf

Samacheer Kalvi 9th Science Solutions Chapter 6 Pdf

Tamilnadu Board Samacheer Kalvi 9th Science Solutions Chapter 6: Tamilnadu State Board Solution Class 9 Science Chapter 6 – LIGHT.

Samacheer Kalvi 9th Science Solutions Chapter 6: Overview

Board Samacheer Kalvi
Class 9
Subject Science
Chapter 6
Chapter Name LIGHT

Samacheer Kalvi 9th Science Solutions Chapter 6 Pdf

Chapter 6

Light

Choose the correct answer.

1) 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°

Ans:  b) 45°

Because, when we incident light at an angle of incidence 0° and  90° there will be no refraction of light takes place.

2) _____ is used as reflectors in torchlight.

a) Concave mirror

b) Plane mirror

c) Convex mirror

Ans:  a) Concave mirror

The mirrors used are concave mirrors.

Because, if we place the bulb very near to the focus of reflector then only we get the parallel beam of light which is highly concentrated and we can see objects easily and clearly.

3) We can create enlarged, virtual images with

a) Concave mirror

b) Plane mirror

c) Convex mirror

Ans:  a) Concave mirror

Because, if we put the object between P and F in case of concave mirrors then the image obtained is virtual and enlarged. We cannot obtain the enlarged image by using convex mirror and plane mirror

4) When the reflecting surface is curved outwards the mirror formed will be

a) Concave mirror

b) Convex mirror

c) Plane mirror

Ans:  b) Convex mirror

Because, the reflecting surface of convex mirror is curved outwards.

5) When a beam of white light passes through a prism it gets

a) Reflected

b) Only deviated

c) Deviated and dispersed

Ans:  c) Deviated and dispersed

Because, light enters from air medium to prism and then from prism to again air medium and optical density of both the medium is different.

6) The speed of light is maximum in

a) Vacuum

b) Glass

c) Diamond

Ans:  a) Vacuum

Because, the speed of light is maximum in vacuum and it is equal to 3*108 m/s

State whether true or false. If false, correct the statement.

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

Ans:  True

Because, the angle of deviation depends on the refractive index of the glass.

2) If a ray of light passes obliquely from one medium to another, it does not suffer any deviation.

Ans: False

Because, if a ray of light is passed from one medium to other then it get refracted due to the different optical densities of the medium.

3) The convex mirror always produces a virtual, diminished and erect image of the object.

Ans:  True

Because, the convex mirror always produces a virtual, diminished and erect image of the object.

4) When an object is at the center of curvature of concave mirror the image formed will be virtual and erect.

Ans: False

Because, when an object is at the center of curvature of concave mirror the image formed will be real and inverted.

5) The reason for brilliance of diamonds is total internal reflection of light.

Ans:  True

Because, the brilliance of diamond is only due to the total internal reflection of light.

III. Fill in the blanks.

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

Ans:In going from a rarer to denser medium, the ray of light bends towards the normal.

Because of the difference in optical densities of the medium.

2) The mirror used in search light is _____.

Ans: The mirror used in search light is concave mirror.

Because, if we place the bulb very near to the focus of reflector then only we get the parallel beam of light which is highly concentrated and we can see objects easily and clearly.

3) The angle of deviation of light ray in a prism depends on the angle of _______.

Ans: The angle of deviation of light ray in a prism depends on the angle ofprism.

4) The radius of curvature of a concave mirror whose focal length is 5cm is _______.

Ans: The radius of curvature of a concave mirror whose focal length is 5cm is 10 cm.

Because, the relation between focal length f and radius of curvature R of concave mirror is given by R = 2f.

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

Ans: Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

Because, concave mirrors are used to concentrate light and to produce heat energy.

Match the following.

Ans:

Ratio of height of image to height of object: magnification

Used in hairpin bends in mountains: Plane mirror

Coin inside water appearing slightly raised: Refraction

Mirage: Total internal reflection

Used as Dentist’s mirror:  Concave mirror

Assertion and reason type questions. Mark the correct choice as:

a) If both assertion and reason are true and reason is the correct explanation.

b) If both assertion and reason are true and reason is not the correct explanation.

c) If assertion is true but reason is false.

d) 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: a) if both assertion and reason are true and reason is the correct explanation

2) Assertion: Incident ray is directed towards the center of curvature of spherical mirror. After reflection it retraces its path.

Reason: Angle of incidence (i) = Angle of reflection (r) = 0o.

Ans: b) if both assertion and reason are true and reason is not the correct explanation

Answer very briefly.

1) According to Cartesian sign convention, which mirror and which lens has negative focal length?

Ans: According to the Cartesian sign conventions, the concave mirror and concave lens both has negative focal length.

2) Name the mirror(s) that can give

Ans:

An erect and enlarged image :

When we place an object between pole of concave mirror and the focus of the concave mirror then the image obtained will be erect and enlarged.

Same sized, inverted image:

When we place an object at the center of curvature of the concave mirror then the image obtained will be of same size and inverted.

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

Ans:

If we placed the object at the focus of the concave mirror then image will be formed at infinity and it is highly enlarged, real and inverted as in fig.

Why does a ray of light bend when it travels from one medium to another?

Ans:

When a ray of light travels from one medium to another then the direction of ray changes because the speed of light is different in different media.

And also the optical density of the medium is different due to which the ray of light bends.

If the ray of light travels from rarer to denser medium it bends towards the normal.

And if the ray of light travels from denser to rarer medium then it bends away from the normal.

What is the speed of light in vacuum? 

Ans:

The speed of light in vacuum is the maximum and it is equal to 3*108 m/s.

And the speed of light in different media is different. Which depends on the optical density of the medium.

And the speed of light in vacuum is always constant.

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

Ans:

Because, the concave mirrors are also called as converging mirrors, which reflect the light to the focal point.

And due to which dr. can see enlarged image of the teeth for correct treatment.

Hence, the concave mirrors produces enlarged image due to which dentist uses them.

VII. Answer briefly.

1) Complete the diagram to show how a concave mirror forms the image of the object. 

Ans:

2) What is the nature of the image?

Ans:  when the object is placed between center of curvature C and focus F of the concave mirror then the image will be formed beyond C and which is enlarged, real and inverted.

3) Pick out the concave and convex mirrors from the following and tabulate them.  Rear-view mirror, Dentist’s mirror, Torchlight mirror, Mirrors in shopping malls, Make-up mirror.

Ans: Concave mirrors: Dentist’s mirror, torchlight mirror, male-up mirror Convex mirrors are used in: mirrors in shopping malls Because, the concave mirror produces the enlarged image for dentist, concentrated beam for torchlight mirror and focus the light on the face in make-up mirrors. The convex mirrors are used in shopping malls because it has a large field view due to which shopkeeper can see all the customers easily.

4) State the direction of incident ray which after reflection from a spherical mirror retraces its path. Give reason for your answer.

Ans: When the ray of light is incident normally on the surface of spherical mirror it retraces its path. Because, when the light ray is incident normally, angle of incidence is zero and hence angle of reflection is also zero. Due to which the ray of light retraces its path after reflection also.

5) What is meant by magnification? Write its expression. What is its sign for real image and virtual image?

Ans:  Magnification is the ratio of height of image to the height of object & it is denoted by m.

m = height of the image/ height of the object =h’ /h

Magnification in terms of image distance & object distance is given as

Magnification m = h’/h = -v/u

Magnification gives the relative extent of magnified image with respect to the original object size.

For real image the magnification is negative, while for the virtual image the magnification will be positive.

6) Write the spherical mirror formula and explain the meaning of each symbol used in it.

Ans: The spherical mirror formula gives the relationship between object distance, image distance & focal length of spherical mirror which is given by,

1/v + 1/u = 1/f

i.e. 1/image distance + 1/ object distance = 1/ focal length

Where, v- is the image distance, the distance of image from the pole of spherical mirror is called as image distance.

u- is the object distance, the distance of object from the pole of the spherical mirror is called object distance.

The distance between the principal focus and the pole of the mirror is called as the focal length of the spherical mirror and it is denoted by f.

VIII. Answer in detail.

a) Draw ray diagrams to show how the image is formed using a concave mirror, when the position of object is:

Ans:

at C

When the object is placed at C of the concave mirror then the image will be obtained at C which has same size, real and inverted as in fig.

ii) Between C and F

When the object is placed between C and F of the concave mirror then the image will be obtained beyond C which is enlarged real and inverted as in fig.

iii) Between F and P of the mirror.

When the object is placed between F and P of the concave mirror then the image will be obtained behind the mirror which is enlarged, virtual and erect.

2) Explain with diagrams how refraction of incident light takes place from  a)  rarer to denser medium

Ans:

When a ray of light travels from rarer to denser medium then after refraction it bends towards the normal. Because the optical density of rarer medium is less than the optical density of the denser medium.

Due to which the speed of light changes and it bends towards the normal.

 

b) Denser to rarer medium:

 Ans:

When a ray of light travels from denser to rarer medium then after refraction it bends away from the normal. Because the optical density of rarer medium is less than the optical density of the denser medium.

Due to which the speed of light changes and it bends away from the normal.

c) Normal to the surface separating the two media.

Ans:

When the ray of light is incident normally on the surface separating two media then it cannot refracted and goes in same direction in second medium also.

And the angle of incidence and angle of refraction both are zero.

Numerical problems.

1) A concave mirror produces three times magnified real image of an object placed at 7 cm in front of it. Where is the image located? (Ans: 21 cm in front of the mirror)

Ans:

Given that, magnification m = 3

Object distance = 7 cm

The magnification produced is given by, m = -v/u

Since, for real image magnification is negative.

V = m*u = 3* (-7)

v = 21 cm

Thus, the image is located at a distance of 21 cm.

2) Light enters from air into a glass plate having refractive index 1.5. What is the speed of light in glass? (Ans: 2 × 108 ms–1)

Ans: Given that, refractive index of glass plate = 1.5

Speed of light in vacuum = 3* 108 m/s We know that, the absolute refractive index is given by Refractive index of glass plate = speed of light in vacuum/ speed of light in glass

Speed of light in glass = speed of light in vacuum/ refractive index of glass

= 3* 108 /1.5 = 2* 108 m/s

Thus the speed of light in glass is 2* 108 m/s

 3) The speed of light in water is 2.25 × 108 ms–1. If the speed of light in vacuum is 3 × 108 ms–1, calculate the refractive index of water.  (Ans: 1.33)

Ans: Given that, speed of light in water = 2.25* 108m/s

Speed of light in vacuum = 3* 108m/s

We know that, the absolute refractive index is given by

Refractive index of water = speed of light in vacuum/ speed of light in water

= 3* 108m/s / 2.25* 108m/s

= 1.33

Thus, the refractive index of water is 1.33

Higher Order Thinking Skills.

1) Light ray emerges from water into air. Draw a ray diagram indicating the change in its path in water.

Ans: When a light ray travels from water into air after refraction it bends away from the normal as shown in fig.

Because, water is denser than the air medium.

2) When a ray of light passes from air into glass, is the angle of refraction greater than or less than the angle of incidence?

Ans:

When the ray of light travels from air into glass then after refraction it bends toward the normal. Because, glass is denser than air medium.

And hence, the angle of refraction is less than angle of incidence as shown in fig.

3) What do you conclude about the speed of light in diamond? If the refractive index of diamond is 2.41?

Ans:

Given that, refractive index of diamond = 2.41

We know that,

Refractive index of medium = speed of light in vacuum/ speed of light in that medium = 3*108/ speed of light in diamond

Speed of light in diamond = 3*108/ 2.41

Speed of light in diamond = 1.244 * 108 m/s

Thus, it is observed that, speed of light in diamond is 1/ (2.41) times the speed of light in vacuum.

That means speed of light is decreased in diamond.

 

Here is your solution of Tamilnadu State Board Solution Class 9 Science Chapter 6 Light.

I hope it will help you to solve your problems & I really appreciate you for being concerned with us. 

Updated: May 26, 2021 — 3:14 pm

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