Interference

a InterferenceCoherent Sources and Sustained Interferencenterference is a natural phenomenon that happens at every place and at every moment. Yet we don’t see interference patterns everywhere. Interference is the phenomenon in which two waves superpose to form the resultant wave of the lower, higher or same amplitude. The most commonly seen interference is the optical interference or light interference. This is because light waves are randomly generated every which way by most sources. This means that light waves coming out of a source do not have a constant amplitude, frequency or phase. The most common example of interference of light is the soap bubble which reflects wide colours when illuminated by a light source.Coherent SourcesTwo sources are said to be coherent when the waves emitted from them have the same frequency and constant phase difference.Interference from such waves happen all the time, the randomly phased light waves constantly produce bright and dark fringes at every point. But, we cannot see them since they occur randomly. A point that has a dark fringe at one moment may have a bright fringe at the next moment. This cancels out the effect of the interference effect, and we see only an average brightness value. The interference is not said to be sustained since we cannot observe it.Characteristics of Coherent SourcesCoherent sources have the following characteristics:• The waves generated have a constant phase difference• The waves are of a single frequencyCoherent Source Example• Laser light is an example of coherent source of light. The light emitted by the laser light has the same frequency and phase.• Sound waves are another example of coherent sources. The electrical signals from the sound waves travel with the same frequency and phase.Types of InterferenceInterference of light waves can be either constructive interference or destructive interference. Constructive interference: Constructive interference takes place when the crest of one wave falls on the crest of another wave such that the amplitude is maximum. These waves will have the same displacement and are in the same phase. for constructive interference, the path difference between the waves from two sources is path difference, QX–PX=n𝜆$$\text{path difference,}QX–PX=n𝜆$$ where n is the integer number.Destructive interference: In destructive interference the crest of one wave falls on the trough of another wave such that the amplitude is minimum. The displacement and phase of these waves are not the same. For destructive interference, we have path difference, QY–PY=(n+1

2)𝜆$$\text{path difference,}QY–PY=(n+\frac{1}{2})𝜆$$ where n is the integer number.Conditions for Interference of Light Waves For sustained interference of light to occur, the following conditions must be met:• Coherent sources of light are needed.• Amplitudes and intensities must be nearly equal to produce sufficient contrast between maxima and minima.• The source must be small enough that it can be considered a point source of light.• The interfering sources must be near enough to produce wide fringes.• The source and screen must be far enough to produce wide fringes.• The sources must emit light in the same state of polarization.• The sources must be monochromatic. Path Difference and Phase DifferenceWhen a wave passes through a medium, the particles of the medium vibrate. When the particles completer one to and fro motion, the wave advances by a distance equal to its wavelength λ. For a complete wave, the wavelength varies in λ and the phase is changed through 2𝜋${\displaystyle 2𝜋}$.. Let there be two waves with a path difference of λ. Then, the phase difference them will be 2𝜋${\displaystyle 2𝜋}$. If the path difference is x, then path difference = 2𝜋

𝜆 × x${\displaystyle =\frac{2𝜋}{𝜆}\times x}$ hence, phase difference=2𝜋

𝜆×path difference$$\text{hence, phase difference}=\frac{2𝜋}{𝜆}\times \text{path difference}$$Optical PathThe product of the distance travelled by the light in a medium and the refractive index of that medium is called the optical path. If d be the distance travelled by the light in a medium of refractive index µ, then by definition, Optical Path=𝜇d$$\text{Optical Path}=𝜇d$$ Young’s Double Slit Experiment

Simulation

S is a narrow vertical slit (of width about 1 mm) illuminated by a monochromatic source of light. At a suitable distance (about 10 cm ) from S, there are two fine slits S1${\displaystyle S_1}$ and S2${\displaystyle S_2}$ about 0.5 mm apart at equidistant from S. when a screen is placed at a larger (about 2m) from the slits S1${\displaystyle S_1}$ and S2${\displaystyle S_2}$, alternate bright and dark bands appear on the screen. The appearance of bright and dark bands are called the fringes.Theory of Interference of Light Suppose S1${\displaystyle S_1}$ and S2${\displaystyle S_2}$ be two fine slits at a small distance d apart in the figure. Let slits are illuminated by monochromatic light from a strong source S of wavelength λ and MN is a screen at a distance D from the double slits. The two waves starting from S1${\displaystyle S_1}$ and S2${\displaystyle S_2}$ superimpose upon each other resulting an interference pattern on the screen placed parallel to the double slit as in the figure.

Theory of interference fringesLet O be the centre between the slits S1${\displaystyle S_1}$ and S2${\displaystyle S_2}$. Draw S1P, S2P ${\displaystyle S_{1}P,S_{2}P}$and OC perpendicular to MN. The intensity of light at a point on the screen will depend upon the path difference between the two waves arriving at the point. The point C on the screen lies on the perpendicular bisector of S1${\displaystyle S_1}$ and S2${\displaystyle S_2}$. Therefore, the path difference between two waves reaching C is zero and hence, they are in phase. So, the point C is the position of maximum intensity. It is called central maximum. Consider a point P at a distance x from C. The path difference between two waves arriving at P is given by path difference=S2P–S1P$$\text{path difference}=S_{2}P–S_{1}P$$ From the geometry in figure, it is found that

	PQ=x-d 2;PR=x+d 2
	And(S2P)2–(S1P)2 =[D2+(x+d 2)2]-[D2+(x-d 2)2]=2xd
	or, (S2P–S1P)(S 2P+S1P)=2xd
	or, (S2P–S1P)=2xd BP+AP
	In practice, point P lies very close to C.
	So S2P≈S1P≈D
	S2P+S1P=D+D=2D
	Path difference=S2P–S1P=2xd 2D=xd D

$$\begin{array}{c}PQ=x-\frac{d}{2};PR=x+\frac{d}{2}\\ \text{And}(S_{2}P{)}^2–(S_{1}P{)}^2=[D^2+(x+\frac{d}{2}{)}^2]-[D^2+(x-\frac{d}{2}{)}^2]=2xd\\ \text{or,}(S_{2}P–S_{1}P)(S_{2}P+S_{1}P)=2xd\\ \text{or,}(S_{2}P–S_{1}P)=\frac{2xd}{BP+AP}\\ \text{In practice, point P lies very close to C.}\\ \text{So}{S}_{2}P\approx S_{1}P\approx D\\ S_{2}P+S_{1}P=D+D=2D\\ \text{Path difference}=S_{2}P–S_{1}P=\frac{2xd}{2D}=\frac{xd}{D}\end{array}$$ The waves from S1${\displaystyle S_1}$ and S2${\displaystyle S_2}$ arriving at a point on the screen will interfere constructively or destructively depending upon this path difference. The phase difference for this path difference is given by Phase difference, 𝜙=2𝜋

𝜆(xd

D )$$\text{Phase difference,}𝜙=\frac{2𝜋}{𝜆}\left(\frac{xd}{D}\right)$$ Bright fringesIf the path difference is an integral is an integral multiple of wavelength λ, then point P is bright. Therefore, for bright fringes

	xd D	=n𝜆
	x	=n𝜆D d…(i)

$$\begin{array}{rl}\frac{xd}{D}& =n𝜆\\ x& =n𝜆\frac{D}{d}\dots (i)\end{array}$$ where n = 0, 1, 2, 3, … The distance of the various bright fringes from the central maximum at C can be found as follows:

	For n=0,x0=0… central bright fringes
	For n=1,x1=𝜆D d…first bright fringes
	For n=2,x2=2𝜆D d…second bright fringes
	For n=n,xn=n𝜆D d…nth bright fringes

$$\begin{array}{c}\text{For}n=0,x_0=0\dots \text{central bright fringes}\\ \text{For}n=1,x_1=\frac{𝜆D}{d}\dots \text{first bright fringes}\\ \text{For}n=2,x_2=\frac{2𝜆D}{d}\dots \text{second bright fringes}\\ \text{For}n=n,x_n=n𝜆\frac{D}{d}\dots n^{th}\text{ bright fringes}\end{array}$$The distance between any two consecutive bright fringes is called fringe width, denoted by β.

	Fringe width, 𝛽=x2–x1=2𝜆D d-𝜆D d=𝜆D d
	∴𝛽=𝜆D d…(ii)

$$\begin{array}{c}\text{Fringe width,}𝛽=x_2–x_1=\frac{2𝜆D}{d}-\frac{𝜆D}{d}=\frac{𝜆D}{d}\\ \therefore 𝛽=\frac{𝜆D}{d}\dots (ii)\end{array}$$Dark fringesIf the path difference is an odd integral multiple of half wavelength λ, then point P is dark. Therefore, for dark fringes;

	xd D	=(2n -1)𝜆 2 where n=1,2,3,…
	or, x	=(2n-1)𝜆D 2d…(iii)

$$\begin{array}{rl}\frac{xd}{D}& =(2n-1)\frac{𝜆}{2}\text{where}n=1,2,3,\dots \\ \text{or,}x& =(2n-1)\frac{𝜆D}{2d}\dots (iii)\end{array}$$Equation (iii) gives the distance of the dark fringes from point C. the distance of the various dark fringes from point C can be calculated as below:

	For n=1,x1=𝜆D 2d…first dark fringe
	For n=2,x2= 3𝜆D 2d…second dark fringes
	For n=n,xn=(2n-1)𝜆𝜆D 2d…nth dark fringes

$$\begin{array}{c}\text{For}n=1,x_1=\frac{𝜆D}{2d}\dots \text{first dark fringe}\\ \text{For}n=2,x_2=\frac{3𝜆D}{2d}\dots \text{second dark fringes}\\ \text{For}n=n,x_n=(2n-1)𝜆\frac{𝜆D}{2d}\dots n^{th}\text{ dark fringes}\end{array}$$The distance between any two consecutive dark fringes is called fringe width β, given as

	Fringe width, 𝛽=x2–x1=3𝜆D 2d-𝜆D 2d=𝜆D d
	∴𝛽=𝜆D d…(iv)

$$\begin{array}{c}\text{Fringe width,}𝛽=x_2–x_1=\frac{3𝜆D}{2d}-\frac{𝜆D}{2d}=\frac{𝜆D}{d}\\ \therefore 𝛽=\frac{𝜆D}{d}\dots (iv)\end{array}$$from equation (ii) and (iv), it is clear that width of the bright is equal to the width of the dark fringe. From these two equations it is clear that fringe width increases as the1. Wavelength increases.2. Distance D of the screen from the sources increases3. Distance between the sources decreases.

Current

Alternating Current

This is class note of Ac current

Acoustic Phenomena

Question Pressure

1.  Sharp knife cuts more easily than a blunt one. Explain with reason.
2. What is the effect on pressure when the area is increased by keeping the magnitude of the force constant ?
3. A man exerts more pressure under his foot when he stands with one foot than when he stands on two foot why ?
4. Prove that, p= F/A.
5. If a man has mass 60 kilogram and the area of his one foot is 150 cm. What is pressure exerted by him on the ground when he stepped with one foot?
6. Anupama has a mass of 30 kg and the surface area that her sandal occupies is 150 cm2. Then what will be the magnitude of pressure if she stands on one foot?
7. What is meant by pressure? Write in which SI unit it is measured.
8. Give any two examples, application of pressure in our daily life?
9. Write two factors that affect the pressure.
10. What is meant by one Pascal pressure?
11. What is meant by pressure?
12. What is the SI unit of pressure?
13. What are the two aspect of or daily life where there is appliaction of pressure?
14. What are the two factors that affect pressure?
15. What is meant by one pascal pressure?
16. What happens to pressure when surface area is increased but the force is kept constant?
17. A man exerts more pressure under his foot when he stands with one foot than when he stands on two foot, why?
18. It is easier to cut with sharp knifes than the blunt ones. Why?
19. If we stand two ladies, one wearing pointed heel shoe and another with flat shoe, in a line. Explain which one will exert more pressure on the ground.
20. What is lactometer?
21. The base of a rectangular vessel measures 10 cm x 18 cm. Water is poured in it to the depth of 4 cm. What are the pressure and force on the base?
22. A girl weight 30 kg and surface area of the heel of her shoe is 100 cm2. Find the pressure exerted on the ground if she stands on her single foot(Take g = 10m/s²).
23. Sharp knife cuts more easily than a blunt one. Explain with reason.
24. What is the effect on pressure when the area is increased by keeping the magnitude of the force constant ?
25. A man exerts more pressure under his foot when he stands with one foot than when he stands on two foot why ?
26. Prove that, p= F/A.
27. If a man has mass 60 kilogram and the area of his one foot is 150 cm. What is pressure exerted by him on the ground when he stepped with one foot?
28. Anupama has a mass of 30 kg and the surface area that her sandal occupies is 150 cm². Then what will be the magnitude of pressure if she stands on one foot?
29. What is meant by pressure? Write in which SI unit it is measured.
30. Give any two examples, application of pressure in our daily life?
31. Write two factors that affect the pressure.
32. What is meant by one Pascal pressure?
33. What is meant by pressure?
34. What is the SI unit of pressure?
35. What are the two aspect of or daily life where there is application of pressure?
36. What are the two factors that affect pressure?
37. What happens to pressure when surface area is increased but the force is kept constant?
38. A man exerts more pressure under his foot when he stands with one foot than when he stands on two foot, why?
39. It is easier to cut with sharp knifes than the blunt ones. Why?
40. If we stand two ladies, one wearing pointed heel shoe and another with flat shoe, in a line. Explain which one will exert more pressure on the ground.
41. What is lactometer?
42. The base of a rectangular vessel measures 10 cm x 18 cm. Water is poured in it to the depth of 4 cm. What are the pressure and force on the base?
43. A girl weight 30 kg and surface area of the heel of her shoe is 100 cm². Find the pressure exerted on the ground if she stands on her single foot(Take g = 10m/s²).
44. Sharp knife cuts more easily than a blunt one. Explain with reason.
45. What is the effect on pressure when the area is increased by keeping the magnitude of the force constant ?
46. A man exerts more pressure under his foot when he stands with one foot than when he stands on two foot why ?
47. Prove that, p= F/A.
48. If a man has mass 60 kilogram and the area of his one foot is 150 cm. What is pressure exerted by him on the ground when he stepped with one foot?
49. Anupama has a mass of 30 kg and the surface area that her sandal occupies is 150 cm². Then what will be the magnitude of pressure if she stands on one foot?
50. What is meant by pressure? Write in which SI unit it is measured.
51. Give any two examples, application of pressure in our daily life?
52. Write two factors that affect the pressure.
53. What is meant by one Pascal pressure?
54. What is meant by pressure?
55. What is the SI unit of pressure?
56. What are the two aspect of or daily life where there is appliaction of pressure?
57. What are the two factors that affect pressure?
58. What is meant by one pascal pressure?
59. What happens to pressure when surface area is increased but the force is kept constant?
60. A man exerts more pressure under his foot when he stands with one foot than when he stands on two foot, why?
61. It is easier to cut with sharp knifes than the blunt ones. Why?
62. If we stand two ladies, one wearing pointed heel shoe and another with flat shoe, in a line. Explain which one will exert more pressure on the ground.
63. What is lactometer?
64. The base of a rectangular vessel measures 10 cm x 18 cm. Water is poured in it to the depth of 4 cm. What are the pressure and force on the base?
65. 
    A girl weight 30 kg and surface area of the heel of her shoe is 100 cm2. Find the pressure exerted on the ground if she stands on her single foot(Take g = 10m/s²).
66. Study the diagram and answer the following questions,
    
1. What is the weight of stone in air?
2. How much upthrust is exerted by liquid on the stone?
3. Calculate mass of the object.
67. The weight of stone when immersed in water is 9N and weight of displaced water is 2N.  Answer the following questions:
    
    
    
1. What reading will the spring balance will show when the stone is taken out from water?
2. Name the principle verified by this experiment. Also state the principle.
68.  A solid object weight 34N in air and 10N in water . What is the upthrust and weight of the liquid displaced ?
69. State the law of floatation. 

Force Question

1.  Write down the relationship of gravitational force with the distance between two heavenly objects and their masses.
2. What is gravitational constant?
3. Calculate the gravitational force between two masses of 10 kg and 20 kg if they are at 10 meter distance.
4. The earth having the mass 6 × 10²⁴ kg revolves around the sun of mass 2 × 10³⁰ kg in a circular orbit of radius 1.5 × 10¹¹ m. Calculate the force of attraction between them (G = 6.67 × 10^-11 Nm²/kg² ).
5. The mass of the earth is 6 × 10²⁴ kg and its radius is 6400 km. What is the mass of a man weighing 977N in a spring balance?
6. What will happen to the gravitational force of attraction between two bodies when the mass of each body is doubled and the distance between them is tripled?
7. State Newton's law of Gravitation. Calculate the force with which the moon pulls every kilogram of water in our rivers given that the moon is 3 × 10⁵ km away from Nepal and the mass of the moon is 7 × 10²² kg.
8. What happens to the force between two objects, if the distance between the object is doubled?
9. At what condition the value of gravitational force (F) becomes 6.67 × 10^-11 N? Show by calculation.
10. What is gravity?
11. Write the differences between free fall and weightlessness?
12. In which direction the force of gravity act?
13. What's the scientific name of human being?
14. why the gravity of jupiter is only two times greater that that of earth though it has extremly greater mass than earth
15. What will be the effect on the gravitational field intensity of the earth if it is squeezed to the size of the moon? (Given: Radius of the earth = 63.8 × 10⁵ m and radius of the moon = 1.7 × 10⁶ m)
16. A paratrooper lands safely when jumped from a great height, why?
17. Why is the value of "g" greater in Terai region than the Himalayan region?
18. Write three differences between acceleration due to gravity (g) and gravitational constant (G).
19. It is difficult to lift a large stone on the surface of the earth but easy to lift small one, why?
20. The value of "g" is more at poles than at the equator, why?
21. If an iron ball and a feather are dropped simultaneously from the same height in vacuum which one will strike the ground first and why?
22. A feather and a coin fall simultaneously on the surface of the moon, why?
23. The probability of getting hurt is more when a man jumps from a significant height, why?
24. If the mass of the moon is 7.2 × 10²² kg and radius 1.7 × 10⁶ m, what will be acceleration due to gravity of the moon? What will be the weight of a man of 60 kg mass of the moon?
25. The radius of the earth is 6.4 × 10³ km height of the Mount Everest is 8848 m. If the value of "g" at the surface of the earth is 9.8m/s², calculate the value of g at the top of Mount Everest. Also find the weight of the body of mass 25 kg on the top of the Mount Everest.
26. The acceleration due to gravity on the earth is 9.8 m/s². What do you meant by this statement?
27. Prove that the acceleration due to gravity(g) is inversely proportional to the radius of the earth(R).
28. The  mass  of the Jupiter is 1.9  x  10²⁷ kg and its radius is 7.1 x 10 ⁷m. What is the acceleration  due to gravity on the Jupiter?  Also, calculate the weight of a person having mass 60 kg in Jupiter.
29. At what condition a coin and a feather fall together? What is the acceleration of the feather and the coin at that instant? Justify your answer.
30. What is free fall?
31. What is meant by weightlessness?
32. What is the difference between fall of a parachute on the earth and that on the moon?
33. In real life, objects do not fall freely. Give reason.
34.   In the figure below, two identical metal balls A and B having equal masses are being dropped towards the surface of moon and earth. Analyse the given data and answer the following questions: 
    
    
    
1.  If both the metal balls are released simultaneously, which one does strike the ground faster? Show with calculation.
2. A person lifts 30kg on the surface of the earth. How much mass can he lift on the surface of the moon if he applies same magnitude of force?
35.  A meteor is falling towards the Earth. If mass and radius of the earth are 6x10²⁴ kg and 6.4x10³ km respectively. Find the height of meteor from the earth's surface where its acceleration due to gravity becomes 4 m/s². The weight of a body decreases in a coal mine, why?
36. The gravitational force produced between any two objects kept 2.5x10⁴ km apart is 580N. At what distance should they be kept so that the gravitational force becomes half.
37. Clarify the statement, "acceleration due to gravity of the earth is 9.8 m/s²"
38. How much time does a stone take to reach on the surface of the earth drop from the height 20 m and what will be its acceleration due to gravity after 3 seconds. (g = 10 m/s²)
39. Atmosphere is present around the surface of earth but it is not present in the moon, why? The mass of Jupiter is 319 times mass of the earth and its radius is 11 times that of earth. Calculate the acceleration due to gravity on surface of Jupiter also calculate the mass of an object in Jupiter whose mass in Earth is 85kg.

10 Science Video Class

  Video Class

SEE Class 10 complete Video Class

Force

https://www.youtube.com/watch?v=icHX0JYarYA

Pressure 1

https://www.youtube.com/watch?v=Ncvt2eStsmo...

Pressure 2

https://www.youtube.com/watch?v=tkAhaXfxL9o...

Energy

https://www.youtube.com/watch?v=jIcUXiYrqAo...

Heat

https://www.youtube.com/watch?v=Fao5Yp2CtEE...

Light

https://www.youtube.com/watch?v=EaltAK_-JiA...

Electricity and magnetism 1

https://www.youtube.com/watch?v=36PoFU0T57s...

Electricity and Magnetism 2

https://www.youtube.com/watch?v=w05QvoBfak8...

Electricity and Magnetism 3

https://www.youtube.com/watch?v=VOoMr6vo-H8...

Classification of Elements

https://www.youtube.com/watch?v=iTBTWGznfJ8...

Chemical Reaction

https://www.youtube.com/watch?v=Fq6Tcdkxsjo...

Acid Base and Salt 1

https://www.youtube.com/watch?v=17UTbkD3x5w...

Acid Base and Salt 2

https://www.youtube.com/watch?v=Hs6Dq04VkPU...

Some Gases

https://www.youtube.com/watch?v=m6eHINwH7so...

Metals

https://www.youtube.com/watch?v=bwXzn0MQ6DQ...

Hydrocarbons

https://www.youtube.com/watch?v=IuiOkd-72sY...

Materials used in Daily Life 1

https://www.youtube.com/watch?v=iUA48qEcToQ...

Materials used in daily life 2

https://www.youtube.com/watch?v=h-Vred2DFls...

Invertebrates

https://www.youtube.com/watch?v=nmSNS519ZA8...

Nervous and Glandular System

https://www.youtube.com/watch?v=_r0n1-YquYk...

Circulatory System

https://www.youtube.com/watch?v=97IT9G6uU6k...

Chromosome and Sex Determination

https://www.youtube.com/watch?v=hPBUzT0v1a0...

Asexual Reproduction 1

https://www.youtube.com/watch?v=XUQ26EMi5No...

Asexual Reproduction 2

https://www.youtube.com/watch?v=EOJ2TQtvDJ8...

Heredity

https://www.youtube.com/watch?v=2eIkM_Opj6A...

Environment Pollution

https://www.youtube.com/watch?v=fusb2Xl6Tyw...

History of Earth

https://www.youtube.com/watch?v=5Cq_5KRawfA...

Atmosphere

https://www.youtube.com/watch?v=ILuYRw3ZPqo...

Universe

https://www.youtube.com/watch?v=XIgSr_vd0SA...