Class 12 Physics Electromagnetic Induction AC Generator

AC Generator

• An electrical generator is a device that converts mechanical energy to electrical energy.
• The generation of alternating currents (ac) is based on the phenomenon of electromagnetic induction.
• Whenever the magnetic flux changes an emf will be induced in the coil.
• AC generator is a device that converts mechanical energy into electrical energy(alternating currents).
• AC generator is an example of inducing an emf or current in a loop by varying the magnetic field and area vector.

Principle:-

• Current is induced in a loop through a change in its orientation or a change in its effective area.
• Induced emf is produced either by changing θ or by changing the area vector.
• Direction of current is given by Fleming’s right hand rule.
• Direction of the current in the circuit changes by the up and down movement of the loops.

Construction:-

• It consists of 2 poles(north and south) of a magnet in order to have uniform magnetic field.
• There is a coil of rectangular shape also known as armature.
• The armature is connected to 2 slip rings.
• Slip rings helps in electrical contact with the brushes.It does not change current direction.
• The slip rings provide a continuous connectionwith the wire around the armature.
• These slip rings are attached to carbon brushes.
• The rectangular coil is capable of rotating about an axis which is perpendicular to the magnetic field.
• The axis of rotation is known as axle.

Working:-

• At initial time t=0;θ =0 where θ = angle between magnetic field (B) and area vector.
• Magnetic flux Φ =BA as cos 0 =1.
• When the coil rotates with the angular velocity ω;
• After time t, θ = ωt;
• Φ(t) =BA cosθ = BA cosωt (because θ is changing as a result magnetic flux is also changing)
• Therefore change in flux occurs; By Faraday’s Law there will be induced emf.
• Induced emf e=- N (dΦ/dt); where N = number of turns.
• = –Nd(BA cosωt)/dt
• e=NBAωsinωt
• As sinωt is a periodic function,therefore it varies from -1 to +1.
• Minimum value of e= - NBAω and maximum value of e=+ NBAω.
• Therefore e =e0sinωt where e0=NBAω
• Therefore Induced current will change periodically.
• As the current is changing periodically that is why it is called as alternating current.
• Rod is getting rotated by some external means; therefore rotation of rod is mechanical energy.
• This mechanical energy is getting converted toinduce emf because of which induced current is produced.
• Therefore because of mechanical energy alternating current is generated.As a result electrical energy is generated.

Types of Generator:-

1. Hydro-electric generators:Power of flowing water is used to rotate the rectangular coil.
2. Thermal generators: - When thermal power is used to rotate the rectangular coil.
3. Power generators

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