Knowledge in Class XII

Magnetic effects of current

The rate of flow of charge is called current.It is always directed from +ve to -ve terminal of the circuit.It is a scalar quantity as it doesn't obey the law of vector addition.Its S.I unit is Ampere. Ohm's law:The potential difference across the two ends of the resisitor is directly proportional to current flowing through it provided the temparature remains same.                                                                                                                 V=IR The opposition to the flow of current is called resistance .It depends upon length,cross-sectional area ,temparature & the nature of the material.Its S.I unit is ohm.                                                                                                                  R=pL/A where,p  is the resistivity of the material. Biot-Savart law The magnitude of a magnetic field at any point due to a current carrying conductor depends upon the current flowing through it,the length element,sin of angle between the position vector and current & inversely proportional to the square of distance of the point from the conductor. ~applications~ 1.Magnetic field due to a straight current carrying conductor. 2.Magnetic field at the centre of the current carrying coil. 3.Magnetic field at the axis of the current carrying coil. Lorentz force When a charge particle moves in a region having both electric & magnetic field then it will experience force by both electric & magnetic field.The vector sum of these two field together is called lorentz force. Cyclotron It is a device which is used to accelerate charge particles in successive steps under the influence of both electric & magnetic field.It consists of two DeesThe electric field helps in accerlation of the particles & the magnetic field helps in circulation of those charged particles in the two semicircular hollow dees separated by a small distance which is set by an alternate source.The whole setup is placed perpendicularly between two pole pieces of magnet.It is only applicable for charged particles because of the relativistic increase in the mass of the charged particles which makes it less energetic.

Electromagnetic Induction

The no. of magnetic field lines passing perpendicularly to a surface is called as magnetic flux.Its S.I unit is Tesla m2 Faraday's experiment He maintained arelative motion between a magnet & a closed coil containing a galvanometer.He found that whenever the northpole of a magnet was moving away or toward the coil the galvanometer showed deflection.This shows that due to the presence of magnet some field lines are connected to the coil,whenever the position of the coil changes the magnetic field lines linked with the coil also changes. For this,an emf is induced in the coil which lasts as long as the change in magnetic flux continues.This is called electromagnetic induction. Lenzs law An emf is produced in the coil such that it opposes the cause which produces it. Whenever the northpole of the magnet was moved towards the coil an induced current is generated in an anticlockwise manner & if the northpole of the magnet is moved away from the coil,the induced current is generated in the clockwise manner. Motional emf The developement of emf in a conductor or a coil when it is moved in a fixed magnetic field. Self-induction Whenever there's a change in emf in a conductor or a coil due to change in its own current is called self-induction Mutual-induction Whenever there's a change in the secondary coil due to the change in current in the primary coil is called mutual induction. 

English grammar vocabulary synonyms

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