Laws of resistance: i) The resistance (r) of a conductor of given material is directly proportional to its length (l) when temperature and area of cross-section remains constant.
ii) The resistance of a conductor of a given material is inversely proportional to the area of the cross-section when length and temperature remains constant.
Joule's Law: Joule's Law states that the amount of work done in different ways produces the same quantity of heat in all cases and is directly proportional to heat produced. W ∝ Q
Faraday's Law of electrolysis: ★ First Law: This Law states that the mass (m) of ions liberated from an electrolyte is directly proportional to the strength of the current (i) and the time (t) for which the current flows.
m ∝ it
Second Law: This law states that when the same quantity of electricity passes through different electrolytes, the masses of ions liberated at the respective electrodes are proportional to their chemical equivalents.
Maxwell's Cork - screw - rule: When the head of a cork screw is rotated such that the tip of the screw advances in the direction of the current, then the direction of rotation of the head represents the direction of the magnetic
field around the conductor.
Ampere's right hand rule: When a current carrying conductor is held in right hand such that the thumb points along the direction of the current, then the remaining fingers indicate the direction of the magnetic lines around the conductor.
Lenze's Law: The induced current will appear in such a direction that it opposes the change that produced it.
Fleming's right hand rule: When the thumb, fore finger, and central finger of the right hand are stretched mutually perpendicular to each other and are held such that the fore finger is along the direction of magnetic
field and the thumb is along the direction of motion of the linear conductor, then the central finger points along the direction of the induced current or e.m.f.
Faraday's law of electromagnetic induction: This law states that the induced e.m.f. in a closed circuit (coil) is equal to the negative rate at which the magnetic flux through it changes.
Bohr's postulates: i) The electrons in an atom revolve around the nucleus in circular orbits just like planets revolve around the Sun.
ii) The electrons revolve only in certain permitted orbits called 'stationary orbits' and do not radiate energy while in such orbits.
iii) The electron has a definite energy in a stationary orbit. Whenever an electron jumps from one stationary orbit to another, absorption or emission of energy takes place.
Einstein's Mass-Energy equivalence: If Δm is the change in mass, the equivalent energy (E) is given by E = Δmc2, where c is the velocity of light in vacuum.
Law of Radio active disintegration: In any radio active substance, the number of atoms disintegrating per second is directly proportional to the number of atoms present.
Properties of a junction diode: i) A p-n junction diode conducts electricity in forward bias condition and offers low resistance for current flow.
ii) In the reverse bias condition, it offers a high resistance and no current flows in the circuit.
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