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PGTRB:LATEST STUDY MATERIAL:
PHYSICS:
ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT.
The emf may be product or generated by chemical action, by a thermocouple or by electromagnetic induction.
Faraday discovered that an emf is produced in a circuit.
Electromagnetic induction principle is used in motion and generators.
The change in flux linking is done either by moving the electric circuit in a stationary magnetic field or by moving the magnetic field relative to a stationary electric circuit and this induction is called dynamic induction.
Whenever there is a change in the magnetic lines of force or magnetic flux, an induced current is produced in the circuit.
The induced current or emf lasts only for the time for which the lines if force in magnetic flux is actually changing.
The magnitude of the induced emf is equal to the rate at which the magnetic lines of force or magnetic flux changes.
Lenz's Law states that whenever an emf is induced, the induced current is in such a direction as to onsite the change inducting the current.
Lenz's law is in accordance with the law of conservation of energy.
Fleming's right hand rule is applied, when the current is induced in a single circuit and is useful in the case of generators and dynamos. It is also known as Generator Rule.
The property of a coil which enables to induce an emf in it when the current in the coil changes is called self-induction.
One Henry is the self induction of a coil of a coil in which rate of charge of one ampere per second induces an opposing emf of one volt.
A dynamo is a machine used for generating electric current by mechanical energy is changed into electrical energy.
Transformer is a device which converts high voltage with low current into low voltage with high current and vice-versa.
Faraday's Law states that the induced emf is directly proportional to the rate of change of magnetic flux.
Lenz's Law states that the induced current will always oppose the change inducing the current.
Fleming Right Hand Rule is applied in AC and AC generators to find direction of induced current.
Self-Inductance is that property of an electric circuit which causes the circuit to oppose any change of current in the circuit.
Mutual-Inductance in the property of a pair of circuits whereby a change of current in one circuit causes an induced emf in the other circuit.
Induced emf can be generated by changing the magnetic induction B or area A of the coil or the orientation of the coil with the field.
An AC generator has a coil of wire called armature rotating in a uniform magnetic field. The emf induced in an ideal generator is alternating in character. This is achieved by using slip rings and brushes.
A DC generator differs from an AC generator in that the DC generator has a commutator to the armature to deliver an unidirectional current to the external circuit.
Eddy or Foucault's currents are the current induced in large conducting bodies when they are linked with changing magnetic fluxes. It is applied in various practical fields.
Transformer is a device used for increasing or decreasing the AC voltage to increase its efficiency, the various losses are to be minimized.
Electric energy is transmitted from a power house to long distances at high voltage and low current in order to reduce the heating losses in the transmission line considerably.
In AC circuits the current and voltage are in-phase for non-inductive resistors: and 90 degree out of phase for pure inductors or pure capacitors.
According to Faraday's Law of electromagnetic induction the electric field can be produced by time varying magnetic flux.
The induced emf in a conductor is directly proportional to the rate of change of flux.
The unit of magnetic flux is Weber.
In a coil an emf of 5 V induced when a current in the coil changes at the rate of 100 amp/sec. The co-efficient of self-induction of the coil is 0.05H.
Principle of a Transformer is Mutual induction.
The emf in an AC containing only resistance will have current in phase with the applied voltage.
The unit of capacitance reactance is Volt.
If the frequency of AC is such that XL=XC then the current in the circuit is maximum.
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