Samacheer Kalvi 10th Science Solutions Chapter 2 Pdf
Tamilnadu Board Samacheer Kalvi 10th Science Solutions Chapter 2: Tamilnadu State Board Solution Class 10 Science Chapter 2 – OPTICS.
Samacheer Kalvi 10th Science Solutions Chapter 2: Overview
Board |
Samacheer Kalvi |
Class |
10 |
Subject |
Science |
Chapter |
2 |
Chapter Name |
OPTICS |
Samacheer Kalvi 10th Science Solutions Chapter 2 Pdf
Chapter 2
Optics
Exercise:
Choose the correct answer
1) The refractive index of four substances A, B, C and D are 1.31, 1.43, 1.33, 2.4 respectively. The speed of light is maximum in
- a) A
- b) B
- c) C
- d) D
Ans: a) A
Because, more the refractive index, denser is the medium and hence less is the speed of light in that medium as shown in figure.
2) Where should an object be placed so that a real and inverted image of same size is obtained by a convex lens
- a) f
- b) 2f
- c) Infinity
- d) Between f and 2f
Ans: b) 2f
Because, in case of convex lens when the object is placed at a distance 2f, as shown in figure then only real, inverted and of same size image will be obtained.
3) A small bulb is placed at the principal focus of a convex lens. When the bulb is switched on, the lens will produce
- a) A convergent beam of light
- b) A divergent beam of light
- c) A parallel beam of light
- d) A coloured beam of light
Ans: c) A parallel beam of light
Because, the ray of light passing through principal focus emerge out as a parallel beam to principal axis.
4) Magnification of a convex lens is
- a) Positive
- b) Negative
- c) Either positive or negative
- d) Zero
Ans: a) Positive
Because, magnification of a convex lens is positive.
5) A convex lens forms a real, diminished point sized image at focus. Then the position of the object is at
- a) Focus
- b) Infinity
- c) At 2f
- d) Between f and 2f
Ans: b) Infinity
Because, in case of convex lens when the object is at infinity then the image produced will be diminished, point size, and real as shown in figure.
6) Power of a lens is –4D, then its focal length is
- a) 4m
- b) –40m
- c) –0.25 m
- d) –2.5 m
Ans :c) –0.25 m
Because, the power of lens is the reciprocal of its focal length and is given by P= 1/f.
7) In a myopic eye, the image of the object is formed
- a) Behind the retina
- b) On the retina
- c) In front of the retina
- d) On the blind spot
Ans: c) In front of the retina
Because, in this defect, focal length of the eye lens will be decreased and hence far point comes closer. And hence, image of the objects which are at a more distance is formed before the retina.
8) The eye defect ‘presbyopia’ can be corrected By
- a) Convex lens
- b) Concave lens
- c) Convex mirror
- d) Bi focal lenses
Ans: d) Bi focal lenses
9) Which of the following lens would you prefer to use while reading small letters found in a dictionary?
- a) A convex lens of focal length 5 cm
- b) A concave lens of focal length 5 cm
- c) A convex lens of focal length 10 cm
- d) A concave lens of focal length 10 cm
Ans: c) A convex lens of focal length 10 cm
Because, to see nearby objects clearly and distinctly we need a convex lens with focal length 10cm here.
10) If VB, VG, VR be the velocity of blue, green and red light respectively in a glass prism, then which of the following statement gives the correct relation?
- a) VB = VG = VR
- b) VB > VG >VR
- c) VB < VG < VR
- d) VB < VG > VR
Ans: c) VB < VG < VR
Because, velocity of light is maximum for red and then decreases up to blue.
Fill in the blanks:
1) The path of the light is called as ——–.
Ans: The path of the light is called as ray of light.
2) The refractive index of a transparent medium is always greater than —–.
Ans: The refractive index of a transparent medium is always greater than one.
3) If the energy of incident beam and the scattered beam are same, then the scattering of light is called as ——-scattering.
Ans: If the energy of incident beam and the scattered beam are same, then the scattering of light is called as elastics cattering.
4) According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its —–.
Ans: According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its wavelength.
5) Amount of light entering into the eye is controlled by—–
Ans: Amount of light entering into the eye is controlled by iris.
III. True or False. If false correct it.
1) Velocity of light is greater in denser medium than in rarer medium
Ans: False
Correct statement: Velocity of light is greater in rarer medium than in the denser medium.
2) The power of lens depends on the focal length of the lens
Ans: True
3) Increase in the converging power of eye lens cause ‘hypermetropia’
Ans: True
4) The convex lens always gives small virtual image.
Ans: False
Correct statement: The convex lens also gives enlarged and virtual image when it is placed between pole and principal focus of lens.
IV. Match the following:
Ans:
- Retina: Screen of the eye
- Pupil: Pathway of light
- Ciliary muscles: Power of accommodation
- Myopia: far point comes closer
- Hypermetropia: near point moves away
V. Assertion and reasoning type Mark the correct choice as
- a) If both assertion and reason are true and reason is the correct explanation of assertion.
- b) If both assertion and reason are true but reason is not the correct explanation of assertion.
- c) Assertion is true but reason is false.
- d) Assertion is false but reason is true.
Assertion: If the refractive index of the medium is high (denser medium) the velocity of the light in that medium will be small
Reason: Refractive index of the medium is inversely proportional to the velocity of the light
Ans: a) if both assertion and reason are true and reason is the correct explanation of assertion.
Assertion: Myopia is due to the increase in the converging power of eye lens.
Reason: Myopia can be corrected with the help of concave lens.
Ans: b) if both assertion and reason are true but reason is not the correct explanation of assertion.
VI. Answer Briefly
1) What is refractive index?
Ans: Refractive index:
The ratio of speed of light in a vacuum (c) to the speed of light in a medium (v) is called as refractive index of the medium.
It is denoted by μ.
Hence, μ = c/v
The velocity of light traveling through the medium depends on the refractive index of the medium.
2) State Snell’s law.
Ans: Snell’s Law:
The ratio of sine of angle of incidence and the sine of angle of refraction is equal to the ratio of refractive indices of the two media. This is known as Snell’s law and it is given by,
Sini/sinr = μ1/ μ2
Where, i- is the angle of incidence
r- is the angle of refraction
μ1– is the refractive index of first medium
μ2 – is the refractive index of second medium
3) Draw a ray diagram to show the image formed by a convex lens when the object is placed between F and 2F.
Ans:
- Position of object: Between F1 and C1 (2F1)
- Position of the image: Beyond C2 (2F2)
- Size of the image: Enlarged
- Nature of image: Real & inverted
4) Define dispersion of light
Ans: Dispersion of light:
When the white light is passed through the transparent media like glass, water or prism then it is refracted through that medium and get splitted into its constituents colours. This phenomenon of spreading of white light into its components is called as dispersion of light.
5) State Rayleigh’s law of scattering
Ans: In earth’s atmosphere there are lot of molecules or atoms by which sunlight get scattered, this scattering is called as Rayleigh’s scattering.
Rayleigh’s law of scattering:
According to this law, the amount of the scattered light is inversely proportional to the fourth power of its wavelength.
It can be stated as, amount of scattering S α 1/ ʎ4.
That means, scattering is more for shorter wavelength light than longer wavelength light.
The blue colour of the sky is due to the scattering of light.
6) Differentiate convex lens and concave lens.
Ans: Convex lens:
- The convex lens is thicker at the center than at the edges.
- Convex lens is the converging lens as it converge the light incident on it.
- The images produced by convex lens are mostly real images.
- The convex lens is used in the treatment of hypermetropia.
Concave lens:
- The concave lens is thinner at the center than at the edges.
- Concave lens is the diverging lens as it diverge the light incident on it.
- The images produced by concave lens are mostly virtual images.
- The concave lens is used in the treatment of myopia.
7) What is power of accommodation of eye?
Ans: Power of accommodation of eye:
The tendency or ability of the eye lens to focus the objects which are at near and also the objects which are at a distant apart is called as the power of accommodation of eye.
With the help of ciliary muscles of eye we can change the focal length of the eye and thereby we can accommodate the power of eye.
8) What are the causes of ‘Myopia’?
Ans: Myopia which is also called as near-sightedness in which objects which are near to our eyes can be seen clearly and easily but the object which are at a distant apart cannot be seen clearly.
This defect occurs due to the lengthening of the eyeballs. By using concave lens myopia can be treated.
9) Why does the sky appear in blue colour?
Ans:
The blue color of the sky is due to scattering of light by molecules of air and dust particles whose size is very small as compared to wavelength of light.
The wavelength of blue & violet light is small & their scattering is more when the light is passed through them than other colors.
According to Rayleigh’s scattering,
Scattering of light α 1/ λ4
Hence, less the wavelength of light more is the scattering.
The order is, λv<λb….<λr and hence the violet & blue colors are scattered more in atmosphere but violet light is not more sensitive to our eyes and we see blue color mostly, so the sky appears blue.
10) Why are traffic signals red in colour ?
Ans: According to this law, the amount of the scattered light is inversely proportional to the fourth power of its wavelength.
It can be stated as, amount of scattering S α 1/ ʎ4.
That means, scattering is more for shorter wavelength light than longer wavelength light.
The blue colour of the sky is due to the scattering of light.
Hence, as the wavelength of red colour is more, it get less scattered than other colours,
And it travels longer distance without scattering and reach to our eyes. Because of this traffic signals are red in colour.
VII. Give the answer in detail
1) List any five properties of light
Ans:
- Light is nothing but the energy in the form of electromagnetic waves.
- Light has property of rectilinear propagation i.e. it always travels in a straight line path.
- For the propagation of light no medium is required, it also travels through vacuum with the speed equal to 3*108 m/s.
- Light is the electromagnetic wave which is characterized by wavelength λ, velocity v, frequency n and speed c. the relation between wavelength, velocity and frequency is given by, V= n λ
- The different colours of light are having different wavelengths and frequencies.
- Light shows the phenomenon of reflection, refraction, dispersion, scattering etc.
- Light has dual nature i.e. particle as well as wave nature which can be studied in higher classes.
2) Explain the rules for obtaining images formed by a convex lens with the help of ray diagram.
Ans: Following are the rules for obtaining images formed by a convex lens with the help of ray diagram.
- In case of convex lens, the light ray incident parallel to principal axis after refraction passes through the focus on the other side of lens as in fig.
- In convex lens, the ray of light passing through focus after refraction it appears parallel to the principal axis as in fig.
- In convex lens, the ray of light passing through optical center of lens, after refraction emerges without any deviation as in fig.
3) Differentiate the eye defects: Myopia and Hypermetropia
Ans:
Myopia:
- It is also called as near-sightedness in which nearby objects are seen clearly but objects which are at a larger distance cannot be seen clearly.
- Myopia causes due to the lengthening of the eyeballs.
- In this defect, focal length of the eye lens will be decreased and hence far point comes closer.
- And hence, image of the objects which are at a more distance is formed before the retina.
- Concave lens is used in the treatment of myopia.
Hypermetropia:
- It is also called as far-sightedness in which objects which are at a more distance are seen clearly and distinctly but the nearby objects cannot be seen clearly.
- Hypermetropia causes due to the shortening of the eyeballs.
- In this defect, focal length of the eye lens will be increased and hence near point is moved farther.
- And hence, image of the nearby object is formed behind the retina.
- Convex lens is used in the treatment of hypermetropia.
4) Explain the construction and working of a ‘Compound Microscope’.
Ans: Compound microscope:
Compound microscope is used to see the smaller objects as it has more magnification power than the simple microscope.
By decreasing the focal length of the lens used magnification power of compound microscope will be increased.
Construction:
- It consist of two convex lenses, one having shorter focal length which is placed near the object which is called as objective lens or objective piece.
- And other is having larger focal length with large aperture is placed near to observer’s eye which is called as eye lens or eye piece.
- Both these lenses are fixed in a narrow tube so that they can be easily adjusted.
Fig. image formation in a compound microscope
- When the object AB is placed at a distance slightly greater than the focal length of objective lens, a real, inverted and magnified image is formed on the other side of the objective lens.
- Now, the position of eye lens is adjusted such that the image A’B’ will falls within the principal focus of the eye piece which forms the virtual, enlarged and erect image A’’B’’ on the same side of the object.
- The compound microscope is having 50 to 200 times more magnification power than simple microscope.
VIII. Numerical Problems:
1) An object is placed at a distance 20cm from a convex lens of focal length 10cm. Find the image distance and nature of the image.
Ans: Given that, for a convex lens focal length is f = 10cm
Object distance u = -20cm
Then, by lens formula
1/f = 1/v – 1/u
1/v = 1/f + 1/u
1/v = 1/10 + 1/-20
1/v = 1/20
Hence, v = 20 cm
And hence, the nature of the image will be real, enlarged and inverted.
2) An object of height 3cm is placed at 10cm from a concave lens of focal length 15cm. Find the size of the image.
Ans: Given that, for a concave lens the focal length is f = -15cm
Since, the focal length of concave lens is negative.
Object distance u = -10cm
And height h = 3cm
By lens formula,
1/f= 1/v – 1/u
1/-15 = 1/v – 1/ -10
1/v = -1/15 – 1/10 = -1/6
Thus, v = -6 cm
The magnification of concave lens is given by,
Thus, m = v/u = h’/h
Where, u – object distance
v- Image distance
h’ – height of image
h – Height of object
Hence, m = v/u = -6/ -10 = 0.6
Also, m = h’ / h
0.6 = h’/3
Thus, h’ = 1.8 cm
Thus, the height of the image produced will be 1.8cm and its size is smaller than the object.
Higher order thinking (HOT) questions:
1) While doing an experiment for the determination of focal length of a convex lens, Raja Suddenly dropped the lens. It got broken into two halves along the axis. If he continues his experiment with the same lens,
Ans:
- Can he get the image?
Because the lens is broken into two halves along the axis, Raja can continues his experiment by using the same lens to get the image.
- Is there any change in the focal length?
Although the lens is broken, the focal length will remains the same.
2) The eyes of the nocturnal birds like owl are having a large cornea and a large pupil. How does it help them?
Ans: The eyes of the nocturnal birds like owl are having a large cornea, due to the larger image of the insects will be formed and owl will see the insects easily in night also. And the large pupil of nocturnal birds helps in providing the larger path for light to enter in the eyes and to fall on the retina in night time. Because of the, above reasons the nocturnal bird has a large pupil and cornea to see insects easily for their feeding in night.