Physics Vidyapith ✍️

Attenuation in Optical Fibre: The difference in the power of the input optical signals and output optical output signals in optical fibre is known as attenuation in the optical fibre. It is measured in decibels per kilometer $(\frac{dB}{Km})$ and caused by the absorption and scattering of the optical signal in optical fibre. The optical signal strength is reduced when the signal travels in optical fibre over a long distance. The expression for the attenuation of optical signal in optical fibre: $\alpha = - \frac{10}{x(Km)} log \left[ \frac{P_{x}}{P_{\circ}} \right]$ Where $P_{x} \rightarrow $ Power of optical signal at a position $x$ from origin $P_{\circ} \rightarrow $ Power of optical signal at origin The Losses in optical fibre are wavelength-dependent and the attenuation factor depends on the fibre material and manufacturing tolerance. A.) Absorption of optical signal in optical fibre: The absorption of optical signals in optical fibre depends on the a

Optical Fibre Communication: Optical fibre communication is a method of communication in which an optical wave passes through optical fibre by the total internal reflection principle. This optical signal consists of the electrical signal (Also known as information) and the laser beam i.e. a carrier wave. The optical fibre is used as a waveguide or transmission medium in optical fibre communication. Principle of optical fibre communication: In the optical fibre communication principle, the information (such as voice) is first converted into an electrical signal. Then it is modulated onto the laser beam (Also known as a carrier wave). In the modulation process, The electrical signal is superimposed onto the laser beam and the frequency of laser light changes with the frequency of the electrical signal. The optical fibre communication uses the pulse code modulation (PCM) for transmitting the optical signal. Now modulated optical signal passes through the optical fibre or waveguide

History of the Special Theory Relativity (Brief Overview): Special relativity is commonly attributed to Albert Einstein’s 1905 papers. That is certainly justifiable. However, Einstein swiped the ideas of relativity from Henri Poincare, (who developed and named the principle of relativity in $1895$ and a mass-energy relation in $1900$), without giving him any credit or even mentioning his name. He may also have swiped the underlying mathematics he used from Lorentz, (who is mentioned, but not in connection with the Lorentz transformation.) However, in the case of Lorentz, it is possible to believe that Einstein was unaware of his earlier work if you are so trusting. Before you do, it must be pointed out that a review of Lorentz’s $1904$ work appeared in the second half of February $1905$ in Beibl¨atter zu den Annalen der Physik. Einstein was well aware of that journal since he wrote $21$ review journals for it himself in $1905$. Several journals were in the very next issue after t

Heat : 1. Heat is that form of energy which flows from a hot body to a cold body when they are kept in contact. 2. The S.I unit of heat is $joule (J)$. 3. The amount of heat contained in a body depends on mass, temperature and substance of body. 4. Heat of the body is measured by the principle of calorimetry. 5. Two bodies having same amount of heat may differ in their temperature. 6. When two bodies are placed in contact then the total amount of heat is equal to the sum of heat of individual body. Temperature: 1. Temperature is a parameter that determines the direction of the flow of heat while keeping the two bodies at different temperatures in contact. 2. The S.I. unit of temperature is $kelvin (K)$. 3. The temperature of a body depends on the average kinetic energy of its molecules due to their random motion. 4. Temperature of the body is measured by a thermometer. 5. Two bodies at the same temperature may differ in the quantities of heat con

Heat capacity: 1. Heat capacity is the amount of heat energy required to raise the temperature of the entire body by $1^{\circ}C$. 2. Heat capacity depends both on the nature of the substance and the mass of the body. As the mass of the body increases the heat capacity of the body also increases. 3. Heat capacity $C=\frac{Q}{\Delta t}\\ C = mass (m) \times specific \: heat \: capacity (c)$ 4. The unit of Heat capacity is $J-K^{-1}$. Specific heat capacity: 1. Specific heat capacity is the amount of heat energy required to raise the temperature of the unit mass of the body by $1^{\circ}C$. 2. Specific heat capacity does not depend on the mass of the body, but it is the characteristic property of the substance of the body. 3. Specific heat capacity $C=\frac{Q}{m\Delta t} \\ C=\frac{Heat \: Capacity \: (C)}{Mass (m)}$ 4. Its unit is $J-kg^{-l}-K^{-1}$.

Dielectric Materials: Materials that do not allow current to flow through them are called insulators or dielectrics. Dielectric materials are capable of storing electric energy. Dielectric materials do not have free electrons ( in the case of ideal dielectric) because electrons are tightly bound with the nucleus so the conductivity of the dielectric is poor and for an ideal dielectric, it is zero. When a dielectric is placed in an external electric field, atoms or molecules of the dielectric material are polarised due to the creation of an electric dipole in the atoms or molecules, and the internal field is set up in the dielectric material which opposes the external applied electric field, thereby reducing the net electric field and hence the electric potential difference. If these dielectrics are placed between plates of a capacitor, the potential difference will be reduced without affecting the charge on the plates. According to the band theory of solids, A dielectric i

There are the following differences between a potentiometer and a voltmeter given below: Potentiometer: 1.) It is based on null method. 2.) It gives an accurate value of emf. 3.) While measuring emf, it does not draw any current from the cell. 4.) Resistance of potentiometer wire becomes infinite while measuring emf. 5.) It can be used for various experimental purposes. 6.) It can not be taken conveniently from one place to another place. Voltmeter: 1.) It is based on the deflection method. 2.) It does not give an accurate value of emf. 3.) While measuring emf, it draws some current from the cell. Hence it reads slightly less than the actual emf. 4.) The resistance of the voltmeter is high enough but not infinite. 5.) It can be used to measure potential differences only. 6.) It can be conveniently taken from one place to another place.