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amit_physics
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Posts by amit_physics
DEll written and interview questions
Feb 10th
Following dell written and interview questions are provided by Mr. Aayush.
He is recently placed in this reputed company. All the best to him.
Dell written questions:
- Three bells rings at the intervals of 36 seconds, 40 seconds and 48 seconds respectively. They start ringing together at a particular time. When they will start ringing together again?
(1)After 6 minutes
(2) After 12 minutes
(3)After 18 minutes
(4) After 24 minutes More >
Maxwell’s Equations and their derivations
Jan 31st
Let us first discuss the Maxwell equations. In this, let us first derive and discuss Maxwell fourth equation:
1. Maxwell’s Fourth Equation or Modified Ampere’s Circuital Law
Here the first question arises , why there was need to modify Ampere’s circuital Law?
To give answer to this question, let us first discuss Ampere’s law(without modification)
Statement of Ampere’s circuital law (without modification). It states that the line integral of the magnetic field H around any closed path or circuit is equal to the current enclosed by the path. More >
How does a laser work
Jan 18th
One must have seen and if not seen then must have heard the term laser. But if you have seen the laser light emitting from a source, then there should be natural question how does a laser work? Therefore let us discuss how the laser works?
As already discussed in my earlier articles, that the full form of laser is “Light amplification by stimulated emission of radiation”. Therefore it means that in laser light is amplified through a process called stimulated emission. Thus it means that stimulated emission is that process through which laser can be achieved. That is the reason the stimulated emission is known as the principle of laser.
Concepts to learn how does a laser work: More >
Maxwell third equation and its derivation
Jan 17th
Statement.(a) It states that,whenever magnetic flux linked with a circuit changes then induced electromotive force (emf) is set up in the circuit. This induced emf lasts so long as the change in magnetic flux continues.
(b) The magnitude of induced emf is equal to the rate of change of magnetic flux linked with the circuit.
Therefore induced emf= – dφm/dt More >
Maxwells first and second equations and their derivation
Jan 17th
Maxwell’s first equation or Gauss’s law in electrostatics
Statement. It states that the total electric flux φE passing through a closed hypothetical surface is equal to 1/ε0 times the net charge enclosed by the surface:
ΦE=∫E.dS=q/ε0
∫D.dS=q
where D=ε0E= Displacement vector More >
DISTORTIONLESS LINE
Jan 14th
Definition DISTORTIONLESS LINE
A transmission line is said to be distortionless when attenuation constant ‘α’ is frequency independent and the phase shift constant ‘β’ is linearly dependent on the frequency.
Condition for line to be distortionless More >
LOSSLESS TRANSMISSION LINE AND ITS CONDITION
Jan 13th
CHARACTERISTIC IMPEDANCE ,Z0
DEFINITION I:- Z0 is defined as the ratio of the square root of series impedance per unit length ,Z to the square root of shut admittance per unit length,Ỳ
Z0=Z/Y =R+jωL/G+jωc More >
TRANSMISSION LINE AND ITS TYPES
Jan 10th
TRANSMISSION LINES
Transmission lines are used to carry electromagnetic energy from one point to another . It means it transfer from one point to another. Generally it consists of two conductors. It is used to connect a source to a load. The source may be a transmitter or an electric generator and the load may be an antenna. Transmission lines are used for operational frequencies equal to or less than about 3GHz. Above 3GHz they will be replaced by waveguides. More >
Sources of losses in Transmission lines
Jan 10th
The three major sources of losses in RF transmission lines are:
1. Copper Losses:-
(a) I2 R Losses. This is due to the resistance associated with the conductors constituting the transmission lines or in other words this loss is due to power dissipation as a result of heating in pure resistance .This loss is frequently dependent and increases with increase in frequency .[Resistance associated with transmission line cannot be measured with an ohmmeter because at radio frequencies,RF ,the current tends to flow on the conductor surface or very near to the conductor surface due to effect called skin effect. More >
WAVE EQUATION IN FREE SPACE OR LOSSLESS OR NON-CONDUCTING OR PERFECT DIELECTRIC MEDIUM
Jan 9th
WAVE EQUATION IN TERMS OF MAGNETIC FIELD INTENSITY,H
Free space or non-conducting or lossless or in general perfect dielectric medium has following characteristics:
(a) No condition current i.e σ=0,thus J=0( J=σE)
(b) No charges (i.e ρ=0)
Therefore for the above cases, Maxwell’s equations will become More >