Laws of Electromagnetism

Laws of Electromagnetism

• The laws of electromagnetism play an important role in the understanding of the various electromechanical energy conversion devices. These laws are stated by the scientist Faraday and Ampere. The laws are,

1. Whenever the number of magnetic lines of force (flux) linking with a coil or circuit changes, an e.m.f. gets induced in that coil or circuit.

2. The magnitude of the induced e.m.f. is directly proportional to the rate of change of flux linkages i.e. flux x turns of coil.

λ  = Flux linkages = Flux × Turns = ϕ × N

ஃ e = dt/dt    ... (2.3.1)

According to Lenz's law the induced e.m.f. sets up a current in such a direction so as to oppose the cause, producing it. This is called statically induced e.m.f.            

3. If there is a relative motion between a conductor and the flux, e.m.f. gets induced in the conductor. This relative motion is due to physical movement of conductor or magnetic field. Such an induced e.m.f. is called dynamically induced e.m.f.   

4. If the conductor is moving with a velocity v m/s, at an angle O measured with plane of the flux then the induced e.m.f. in the conductor is given by,

e = B l v sin θ V

where B = Flux density in Wb/m²  

 l = Active length of conductor in m

If plane of rotation of conductor is perpendicular to the plane of flux, θ = 90° and e = B l v volts. The direction of such an induced e.m.f. is given by Flemings right hand rule.    

5. If a current carrying conductor is placed in the lines of magnetic field (flux), then it experiences a force.

6. The magnitude of the force experienced by the conductor carrying current I, placed in magnetic field of flux density B is given by,        

F = B I l N

where   I = Current in amperes 

l = Active length of conductor in m

• The direction of this force is given by Fleming's left hand rule.     

• These laws form a base of electromechanical energy conversion process.

Review Question

1. State the laws of electromagnetism.