Physics

Stress-Strain Curve /  प्रतिबल-विकृति वक्र in Curve / प्रतिबल-विकृति वक्र Graph which represents stress value against strain value of the given material , when the material is subjected to increasing pull, is known as stress-strain graph. Stress-strain curves are an extremely important graphical measure of a material’s mechanical properties. किसी पदार्थ में उत्पन्न विकृति तथा प्रतिबल के बीच सम्बन्ध उस पदार्थ का प्रतिबल – विकृति वक्र (stress–strain curve) कहलाता है। प्रतिबल-विकृति वक्र, सामग्री के यांत्रिक गुणों का एक बहुत ही महत्वपूर्ण वक्र है। For detail, watch the video:

Elasticity / प्रत्यास्थता The properties of matter due to which it regains its original length, shape and volume, when the deforming forces have been removed. Deforming Force – A force which produces a change in configuration of the object on applying it, is called a deforming force. In a solids, atoms / molecules are arranged in such a way that each molecule is acted upon by the forces due to neighbouring atoms / molecules. These forces are known as intermolecular forces. For simplicity, the two atoms / molecules in their equilibrium positions (at inter-atomic / molecular distance r = r0) are shown by connecting them with a spring. In fact, the spring connecting the two molecules represents the inter-molecular force between them. On applying the deforming forces, the molecules either come closer or go far apart from each other and restoring forces are developed. When the deforming force is removed, these restoring forces bring the molecules of the solid to their respective ...

Inter-atomic Forces /  अंतर-आण्विक बल The forces between the atoms due to electrostatic interaction between the charges of the atoms are called interatomic forces. These forces are electrical in nature. It is of the order of 10−10 metre. Consider two isolated atoms moving towards each other as shown in Figure. As the atoms approach each other, the following interactions are observed.1.Attractive force A between the nucleus of one atom and electron of the other. This attractive force tends to decrease the potential energy of the atomic system. 2.Repulsive force R between the nucleus of one atom and the nucleus of the other atom and electron of one atom with the electron of the other atom. These repulsive forces always tend to increase the energy of the atomic system. If the net effect of the forces of attraction and repulsion leads to a decrease in the energy of the system, the two atoms come closer to each other and form a covalent bond by sharing of electrons. ...

Screw Gauge / पेंचमापी For details, view the video:

Vernier Caliper / वर्नियर कैलिपर For details, view the video:

Accuracy and Precision / परिशुद्धता और यथार्थता Accuracy refers to the closeness of a measured value to a standard or known value. For example, if in lab you obtain a weight measurement of 3.2 kg for a given substance, but the actual or known weight is 10 kg, then your measurement is not accurate. In this case, your measurement is not close to the known value. Precision refers to the closeness of two or more measurements to each other. Using the example above, if you weigh a given substance five times, and get 3.2 kg each time, then your measurement is very precise. Precision is independent of accuracy. You can be very precise but inaccurate, as described above. You can also be accurate but imprecise. परिशुद्धता (Accuracy), ज्ञात माप के लिए निकटता को संदर्भित करता है । उदाहरण के लिए, यदि लैब में आप किसी दिए गए पदार्थ के लिए 3.2 किलोग्राम वजन मापते हैं, लेकिन वास्तविक या ज्ञात वजन 10 किलोग्राम है, तो आपका माप सही नहीं है । इस मामले में, आपका माप, वास्तविक ज्ञात माप के ...

X – Rays / X – किरणें William Roentgen discovered X-rays in 1895 Roentgen was awarded the Nobel Prize in 1901. When cathode rays strike on heavy metals of high melting point, then a very small fraction of its energy converts into a new type of waves known as X – ray. X-rays are electromagnetic waves of short wavelength in the range of 1 Å to 100 Å. विलियम रॉन्टगन ने 1895 में एक्स- किरणों की खोज रॉन्टगन को 1901 में नोबेल पुरस्कार से सम्मानित किया गया जब कैथोड किरणों उच्च गलनांक की भारी धातुओं पर प्रहार करती हैं तो, उनकी ऊर्जा का एक बहुत छोटा सा अंश एक नई प्रकार की तरंग के रूप में  परिवर्तित हो जाता है जिन्हे एक्स -किरणें कहा जाता है | एक्स-किरणें 0.5 Å से 10 Å की सीमा की कम तरंग दैर्ध्य की  विद्युत चुम्बकीय तरंगें हैं । For details, view the video:

Photo-electric Effect / प्रकाश-विद्युत प्रभाव Discovered by Heinrich Hertz in 1887 Whenever light or electromagnetic radiation fall on a metal surface, it emits electrons. This phenomenon of emission of an electron from a metallic surface when radiation of suitable frequency falls upon it is called photoelectric effect. Emitted electrons are called photoelectrons. 1887 में हेनरिक हर्ट्ज प्रकाश-विद्युत प्रभाव की खोज की गई । जब भी प्रकाश या विद्युत चुम्बकीय विकिरण एक धातु की सतह पर आपतित होते हैं, तो धातु से इलेक्ट्रॉनों का उत्सर्जन होता है जब उपयुक्त आवृत्ति के विकिरण एक धातु की सतह पर आपतित होते है तो इलेक्ट्रॉन के उत्सर्जन की इस घटना है को प्रकाश विद्युत प्रभाव कहा जाता है । उत्सर्जित इलेक्ट्रॉनों को फ़ोटो ईलेक्ट्रॉन कहा जाता है । For details, view the video:

Planck’s Hypothesis / प्लैंक की परिकल्पना In 1900 Planck reported his discovery of a formula that accurately described the shape of a blackbody spectrum for all wavelengths and temperatures. When a black body is heated, it emits thermal radiations of different wavelengths or frequency. To explain these radiations, Max Planck put forward a theory known as Planck’s quantum theory. 1900 में प्लैंक ने एक सूत्र की जिसमें सभी तरंग दैर्ध्य और तापमान के लिए एक ब्लैकबॉडी स्पेक्ट्रम का सटीक वर्णन किया गया था। जब एक कृष्णिका पिंड को गर्म किया जाता है, तो यह विभिन्न तरंग दैर्ध्य या आवृत्ति के उष्मीय विकिरणों का उत्सर्जन करता है। इन विकिरणों की व्याख्या करने के लिए, मैक्स प्लैंक ने एक सिद्धांत को प्रतिपादित किया, जिसे प्लैंक के क्वांटम सिद्धांत के रूप में जाना जाता है। For details, view the video:

LASER / लेसर LASER is an acronym stands for Light Amplification by Stimulated Emission of Radiation Laser is a device that amplifies or increases the intensity of light and produces highly directional light. परिवर्णी शब्द LASER से आश्य है – Light Amplification by Stimulated Emission of Radiation लेजर एक ऐसा उपकरण है जो प्रकाश की तीव्रता को बढ़ाता है व अत्यधिक दिशात्मक प्रकाश पैदा करता है। For details, view the video:

Young’s Interference Experiment / यंग का व्यतिकरण प्रयोग The phenomenon of interference was first observed and demonstrated by Thomas Young in 1801. This experiment is important because it proves wave nature of light. Young’s experiment was based on the hypothesis that if light were wave-like in nature, then it should behave in a manner similar to ripples or waves on a pond of water. 1801 में थॉमस यंग द्वारा व्यतिकरण की घटना को पहली बार देखा और प्रदर्शित किया गया । यह प्रयोग महत्वपूर्ण है क्योंकि यह प्रकाश की तरंग प्रकृति को सिद्ध करता है। यंग का प्रयोग इस परिकल्पना पर आधारित था कि यदि प्रकाश तरंग की व्यवहार करता है, तो उसे तालाब पर पानी की लहर या लहरों के समान व्यवहार करना चाहिए। For details, view the video

Diffraction of Light / प्रकाश का विवर्तन First discussed by Grimaldi ~ 1665 Term diffraction comes from Latin diffringere meaning to break into small pieces Others who studied it included Newton, Gregory, Young, Fresnel Diffraction means the bending of light around an obstacle. The size of the obstacle should be comparable to the wavelength of the light. Diffraction is a wave effect. पहले ग्रिमाल्डी द्वारा वर्ष 1665 में विवर्तन के बारे में चर्चा की गई शब्द ‘विवर्तन’ की उत्पत्ति लैटिन शब्द ‘ diffringere ’ से हुई, जिसका अर्थ छोटे- छोटे टुकड़ों में टूटना है । जिन अन्य वैज्ञानिकों ने इसका अध्ययन किया, उनमें न्यूटन, ग्रेगरी, यंग, फ्रेस्नेल शामिल हैं । विवर्तन का अर्थ है किसी बाधा या रुकावट के चारों ओर प्रकाश का झुकना। बाधा का आकार प्रकाश की तरंग दैर्ध्य के बराबर होना चाहिए विवर्तन, प्रकाश का तरंग प्रभाव है For detail, view the video:

Interference of Waves / तरंगों का व्यतिकरण When two light waves of same frequency having a zero or constant phase difference travel in a medium, in the same direction then due to their superposition, at some points the intensity of light is maximum and some at some other point intensity of light is minimum. This phenomena of redistribution of energy due to superposition of waves is called interference of light waves. जब समान आव्रत्ति की दो प्रकाश तरंगे किसी माध्यम में एक ही दिशा में गमन करती हैं तो अध्यारोपण के सिद्धांत के अनुसार परिणामी तरंग का निर्माण होता है । कुछ स्थानों पर प्रकाश की तीव्रता अधिकतम और कुछ स्थानों पर न्यूनतम शून्य होती है । तरंगों के अध्यारोपण के कारण ऊर्जा के पुनर्वितरण की इस घटना को प्रकाश तरंगों का व्यतिकरण कहा जाता है। For details, view the video:

Coherent Sources / कला सम्बन्ध स्रोत Two sources are said to be coherent when the waves emitted from them have the same frequency and constant phase difference. Two independent sources can never have same wavelength, same frequency and in same phase or having the constant phase difference at a time. Hence, two independent sources of light can ‘t be used as a coherent sources. दो स्रोतों को कला सम्बंध कहा जाता है जब उनसे निकलने वाली तरंगों में समान आवृत्ति और नियत कलांतर होता है। दो स्वतंत्र स्रोतों में कभी भी समान तरंगदैर्ध्य, समान आवृत्ति और एक ही कला या स्थिर कलांतर नहीं हो सकता है। इसलिए, प्रकाश के दो स्वतंत्र स्रोतों का उपयोग कला सम्बंध स्रोतों के रूप में नहीं किया जा सकता है । For details, view the video:

Newton’s Corpuscular Theory / न्यूटन का कणिका सिद्धांत The ‘Corpuscular theory of light was proposed by Newton in 1704. The corpuscular theory states that light is made up of tiny particles called ‘corpuscles’ (little particles) that always travel in a straight line. Light is made up of tiny particles called ‘corpuscles’ having negligible mass. These particles (corpuscles) are perfectly elastic. The corpuscles are emitted from the luminous sources such as Sun, candle, electric lamp etc. The tiny particles (corpuscles) always travel in a straight line in all directions. Each particle (corpuscle) carries kinetic energy with it while moving. The corpuscles travel at high velocity. विख्यात वैज्ञानिक न्यूटन ने सन्‌ 11704 में कणिका सिद्धांत प्रतिपादित किया कणिका सिद्धांत कहता है कि प्रकाश छोटे कणों से बना होता है जिन्हें कॉर्पसपर्स ’(छोटे कण) कहा जाता है जो हमेशा एक सीधी रेखा में गमन करते हैं। प्रकाश छोटे कणों से बना होता है जिनका द्र्व्यमान ’नगण्य’ माना जा सकता है । ये क...

Polarisation of Light / प्रकाश का ध्रुवण The light having electric field oscillations in all directions in the plane perpendicular to the direction of propagation is called Unpolarised light.The oscillation may be resolved into horizontal and vertical component The light having oscillations only in one plane is called polarised or plane polarised light. वह प्रकाश जिसमें विद्युत् वेक्टर का कम्पन, प्रत्येक दिशा में समान रूप से अथवा सममित रूप से, प्रकाश संचरण की दिशा के लम्बवत तल में होता हैं; ऐसे प्रकाश को अध्रुवित प्रकाश (Unpolarised Light) कहते हैं। प्रकाश तरंग के दोलन को क्षैतिज और ऊर्ध्वाधर घटक में विभक्त किया जा सकता है। केवल एक ही तल में दोलन करने वाले प्रकाश को ध्रुवीकृत या समतल ध्रुवीकृत प्रकाश कहा जाता है। For details, view the video:

Superposition of Waves / तरंगों का अध्यारोपण When two or more waves simultaneously pass through the same medium, each wave acts on every particle of the medium, as if the other waves are not present. The resultant displacement of any particle is the vector addition of the displacements due to the individual waves. जब किसी माध्यम में दो या दो  से  अधिक तरंगें साथ चलती हैं  तो, माध्यम के  प्रत्येक कण  का किसी भी क्षण परिणामी विस्थापन सभी  तरंगों के  द्वारा उत्पन्न अलग –अलग विस्थापनों के सदिश योग के बराबर होता है । For details view the video:

Dispersion of Light /  प्रकाश का वर्ण- विक्षेपण The dispersion of light is the phenomenon of splitting of a beam of white light into its seven constituent colours when passed through a transparent medium. It was discovered by Isaac Newton in 1666. Newton discovered that light is made up of seven different colours. He passed a beam of sunlight through a glass prism. The glass prism split the light into a band of seven colours on his wall. He called this band of colours the ‘spectrum’. The order of colours from the lower end of spectrum is violet (V), indigo (I), blue (B), green (G), yellow (Y), orange (O), and red (R). The sequence of the 7 colours so obtained in a spectrum can be remembered by using the acronym ‘VIBGYOR’. The deviation of a beam of a colour depends on its refractive index. The deviation will be higher if the value of refractive index is higher. The refractive index depends on the wavelength of light. The value of refractive index will be lower w...

Huygens Theory – Reflection of Wave / हाइगेंज सिद्धांत – तरंग का परावर्तन for details watch the video

Huygens Theory – Refraction of Wave / हाइगेंज सिद्धांत – तरंग का अपवर्तन For details watch the video :

Huygens Wave Theory of Light /  हाइगेंज का प्रकाश का तरंग सिद्धां त    Wave theory of light was proposed by Christiaan Huygens in 1678 Every point on a wave-front may be considered a source of secondary spherical wavelets which spread out in the forward direction at the speed of light. The new wave-front is the tangential surface to all of these secondary wavelets. It helps us to locate the new position and shape of the wavefront at any instant, knowing its position and shape at any previous instant. In other words, it describes the progress of a wave front in a medium. Light motion is a wave motion. Each point on a light source acts as a source of disturbance and sends out waves in all directions. These waves fall upon the retina of the eye and cause the sensation of light. These waves move in all imaginary, isotropic and hypothetical medium ‘ether’. Ether was assumed to have large elasticity and low density. Light waves in ethereal medium are transvers...

Critical Angle & Total Internal Reflection / आंतरिक कोण एवं पूर्ण आंतरिक परावर्तन When a ray of light travels from denser medium to rarer medium, then refracted ray bends away from normal. In this position incident angle is lower than refracted angle. On increasing the angle of incidence, the angle of refraction also increases. At a particular value of angle of incidence, the angle of refraction becomes 900 . This angle of incidence for which angle of refraction is 900 is called critical angle. When a ray of light passes from denser medium to rarer medium and angle of incidence is greater than critical angle, then the ray of light reflects back to the same medium following the laws of reflection. This phenomenon is called total internal reflection. जब प्रकाश किरण, सघन माध्यम विरल से माध्यम में प्रवेश करती है, तो आवर्तित किरण अभिलम्ब से दूर हट जाती है । इस अवस्था में आपतन कोण, आवर्तन कोण से कम होता है जैसे-जैसे आपतित कोण का मान बढ़ाते है, अपवर्तित कोण का मान भी बढ़ जाता...

Fringes / फ़्रिंज Fringes are bands of contrasting brightness or darkness produced by diffraction or interference of radiation. The alternate dark and bright bands obtained on screen are known as fringe pattern. Distances between fringes are usually very small, because of the short wavelength of light. Fringes are clearer and more numerous when produced with light of a single color. Diffraction fringes are formed when light from a point source, or from a narrow slit, passes by an opaque object of any shape. Interference fringes are obtained by bringing together two or more beams of light that have originated from a common source. The distance between any two consecutive bright or dark fringe is known as fringe width. Symbolically the fringe width ′β’ is given by β=  λD/d (λ)Wavelength of the light used, (D) distance of the screen from the slits and (d) distance between two slits. फ्रिंजेस, विवर्तन या व्यतिकरण से उत्पन्न दीप्त क्षेत्र या अदीप्त क्षेत्र बैंड होते हैं ।...

Wavelet / तरंगाग्र When a stone is dropped in a still water, waves spread out along the surface of water in all directions with same velocity. Every particle on the surface vibrates. At any instant, if we take a photograph of the surface of water would show circular rings on which the disturbance is maximum. All the particles on such a circle are vibrating in phase, because these particles are at the same distance from the source. Such a surface which envelopes the particles that are in the same state of vibration is known as a wave front. Every light emitting source emits continuous and parallel ray and if some points or particles of the wave lie on the same plane and have same frequency and wavelength i. e. they have same phase then those particles in that plane is known as a wavefront. So, we can say that Wave front is an imaginary surface representing corresponding points of a wave that vibrate in unison. Wavefront is usually perpendicular to the direction of propagatio...