Laws in electromagnetism
Law of conservation of electric charge-
The algebraic sum of positive and negative charges in an isolated system remains constant.
Coulomb's law-
The electrostatic force of interaction between two point electric charges is directly proportional to the product of the charges, inversely proportional to the square of the distance between them and acts along the straight line joining the two charges.
q1q2
F = k r²
Principle of superposition of electric forces-
When a number of charges are interacting, the total force on a given charge is the vector sum of the individual forces exerted on the given charge by all the other charges.
Principle of superposition of electric fields-
The electric intensity at a point due to several charges is the vector sum of electric intensities produced by each charge individually in the absence of other charges.
Gauss's law-
The surface integral of the electric field intensity over any closed surface in free space is equal to 1/ε○ times the net charge enclosed within the surface.
Ohm's law-
At constant temperature, the electric current flowing through a conductor is directly proportional to the potential difference across the two ends of the conductor.
Kirchhoff's first law-
The sum of the currents flowing towards a junction is equal to the sum of the currents leaving the junction.
Kirchhoff's second law-
The algebraic sum of all the potential drops and emf's along any closed path in a network is zero.
Joule's law of heating-
The amount of heat developed in a passive resistance by the passage of steady electric current through it is proportional to the square of the electric current, the resistance of the conductor and the time for which the current flows.
Q = I²Rt
Faraday's first law of electrolysis-
The mass of the ions deposited or liberated in electrolysis is directly proportional to the quantity of electricity .i.e., charge passed through the electrolyte.
Faraday's second law of electrolysis-
When the same electric current is passed through several electrolytes for the same time, the masses of the various ions deposited or liberated at each of the electrodes are proportional to their chemical equivalents .i.e., equivalent weights.
Seebeck effect-
The phenomenon of generation of an electric current in a thermocouple by keeping its junctions at different temperatures is called seebeck effect or thermoelectric effect.
Thermoelectricity- law of successive temperatures-
For a given thermocouple, the emf for any specified temperature difference is equal to the sum of the emf's corresponding to any smaller intervals into which the given range of temperature may be sub-divided.
Thermoelectricity- law of successive metals-
The insertion of an additional metal or metals into any thermoelectric circuit does not change the effective emf of the circuit, provided that both the ends of each such conductor are at the same temperatures.
Peltier effect-
The absorption or evolution of heat at a junction of two dissimilar metals when current is passed is known as peltier effect.
Thomson effect-
The absorption or evolution of heat along the length of a conductor on passing current through it, when its two ends are kept at different temperatures, is known as Thomson effect.
Biot-savart's law-
The magnetic field due to an infinitesimally small element of length dl of a current carrying conductor is given by
μ○ sinθ
dB = 4π r²
Right hand thumb rule-
Imagine grasping the conductor in the palm of your right- hand so that the thumb points in the direction of flow of current. Then the other four fingers curve in the direction of B with the finger tips pointing along B.
Maxwell's cork screw rule-
Imagine a right-handed cork screw placed along the current-carrying conductor. If the screw is rotated so that it moves in the direction of flow of current. Then the direction of rotation of the thumb gives the direction of magnetic lines of force.
Fleming's left hand rule-
Stretch the first finger, the central finger and the thumb of your left hand in mutually perpendicular directions. If the first finger points in the direction of the magnetic field, the central finger points in the direction of motion of the charge, then the erect thumb gives the direction of the force.
Ampere's circuital law-
The line integral for a closed curve is equal to
μ○
times the net current I through the
area bounded by the curve.
=
μ○I
Fleming's right hand rule-
Stretch the thumb and the first two fingers of your hand in mutually perpendicular directions. If the first finger points in the direction of the magnetic field, the thumb in the direction of motion of the conductor, then the central finger points in the direction of the induced emf or induced current in the conductor.
Faraday's first law in electromagnetic induction-
Whenever there is a change in the magnetic flux linked with a circuit, an emf and consequently a current is induced in the circuit.
Faraday's second law in electromagnetic induction-
The magnitude of the induced emf is directly proportional to the rate of change of magnetic flux linked with the circuit.
Lenz's law-
The direction of the induced emf or induced current is such that it opposes the change that is producing it.
