Electromagnetism, EMI and AC Flashcards
What is magnetic flux?
Product of magnetic flux density normal to the surface and the area of the surface.
ø = BA (cos θ)
Define magnetic flux density.
Force acting per unit current per unit length of the conductor when conductor is placed at right angles to the field.
Define magnetic flux linkage.
It is product of number of turns of coil, N, and magnetic flux, ø, passing through the coil.
Define tesla.
It is the magnetic flux density when a straight wire carrying current at 1 ampere, placed at right angles to magnetic field, experiences a force per unit length of 1 N m-1.
What is weber?
It is quantity of magnetic flux passing through an area of 1 square metre (m2) when flux density normal to the area is 1 tesla (T).
1 W = 1 T m2
State Faraday’s Law.
Induced emf in a circuit is directly proportional to the rate of change of flux linkage or rate of cutting of magnetic flux.
State Lenz’s Law.
The direction of induced emf is such that it tends to oppose the flux change causing it if current flows.
What is meant by root-mean-square value?
It is the value of steady direct current (D.C.) that would dissipate heat at the same rate as the alternating current (A.C.) in a resistor.
Why is AC preferred for transmission?
It can be stepped up or down through the use of transformers. Since high voltage is suited for transmission to reduce power loss, AC is used as a source.
