Coupon Accepted Successfully!


Periodic EMI

Suppose a rectangular coil having N turns placed initially in a magnetic field such that magnetic field is perpendicular to its plane as shown in Fig. 11.
For uniform rotational motion with ω, the flux linked with coil at any time t
φ = NBA cos θ = NBA cos ωt
where φ0 = NBA = maximum flux
ω – Angular speed
v – Frequency of rotation of coil
R – Resistance of coil
Fig. 11

Induced emf in coil

Induced emf also changes in periodic manner. That is why this phenomenon called periodic EMI
88673.png ⇒ e = e0 sin ωt
where e0 = emf amplitude or maximum emf = NBA ω = φ0ω

Induced current

At any time t,
where i0 = current amplitude or maximum current


  • In motional emf 89206.png are three vectors. If any two vectors are parallel, no flux cutting.
Fig. 12
  • A piece of metal and a piece of non-metal are dropped from the same height near the surface of the earth. The non-metallic piece will reach the ground first because there will be no induced current in it.
  • If an aeroplane is landing down or taking off and its wings are in the east–west direction, then the potential difference or emf will be induced across the wings. If an aeroplane is landing down or taking off and its wings are in the north–south direction, then no potential difference or emf will be induced.
  • When a conducting rod moving horizontally on equator of earth no emf induces because there is no vertical component of earth’s magnetic field. But at poles BV is maximum so maximum flux cutting. Hence, emf induces.
When a conducting rod falling freely in earth’s magnetic field such that its length lies along East–West direction then induced emf continuously increases wrt time and induced current flows from West–East.

Test Your Skills Now!
Take a Quiz now
Reviewer Name