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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.
• The phenomenon or resonance is used in Radio.